Naples:life,death &
                Miracle contact: Jeff Matthews

The Subsoil of Naples
Part 2, chapter 3, 4, 5, 6

    chapter 3 - directly below      chapter 4, here               chapter 5, here           chapter 6, here
(Distribution of Cavities)      (Underground Waters)     (geotechnical problems)

How Rock Mining and Underground Structures
Can Cause the Subsoil to Shift
prepared by Dr. Eng. Dante Bard

1) Methods of mining

A brief review of how extracting minerals from the subsoil for construction material may explain some of the problems of cave-insand shifting in the terrain.
Pozzolana and sand. Pozzolana, whether from primary sedimentation or disturbed in some fashion (and thus mixed with sand strata), has always been extracted in the simplest way: open-pit cutting and subsequent removal of inclined wall fronts either by cutting steps into the surface or by using the natural slope of the terrain. Since the beginning of the 1900s, there have a few rare examples of funnel extraction (the Canadian system) when situations require that the panoramic view from a hill not be disturbed. With the longer reach of modern mechanical equipment, however, extraction is done only from the foot of the hill, knocking down the slope as work proceeds.
Lapilli pumice. Leaving aside the narrower pumice strata that have been spoiled by surrounding terrain, extractable lapilli are found in level strata as thick as two meters at different elevations in the countryside. The use of white pumice is ancient, indeed. It has always been worked as the stone for barrel vaults, domes. etc. and is the pride of the building trade in the Gulf of Naples. The mixture of pumice with primary pozzolana and slaked lime, thrown and worked onto curved surfaces (to avoid cracks caused by fluctuating ambient temperature) has been use for two-thousand years.
In building multi-story and lighter-weight structures, however, they have tried to use the same material in the form of slabs or plates mounted into a framework (as in the protective coverings of terraced roofs).The cracks between plates, however, make the material much less efficient in coping with outside changes of temperature. Lapillo has a great many uses today in what is called “prefabricated” construction. After a period of time when it was little used, white lapillo has made a comeback as partition blocks and load-bearing supports in basements.
Today, only open-pit extracting is permitted, but until the first decades of this century [the 1900s], the material was extracted from underground chambers and shafts with the rare exception of smaller openings,where possible, cut into the front of pozzolana quarries. Access was by way of circular, vertical well shafts, never covered, to the bank of lapillo pumice generally at about 6 to 10 meters below the surface, occasionally deeper. From the bottom of the well, at the base of the lapillo bank, a series of shafts were then dug out like spokes off of a hub, each a few meters wide and from 10 to 15 meters long. When the extraction was finished, only the central shaft was filled back up. Waste rock was used until a bit before the surface and the rest was filled with earth.
The depth of the shafts and the presence of tree roots usually meant that the level surface above did not sink in to any noticeable degree. Below ground, however, around the central well, where it wasimpossible to shore up the sections where the spokes joined the hub, the space was precarious and could cave in. Such cave-ins became more likely if overlying soil was disturbed by the removal of large trees with their root systems and where construction on the surface interfered with an already shaky equilibrium.* This kind of digging always took place in those parts of town where the primary minerals were the most abundant; that meant the hills of Vomero, Capodimonte and Capodichino.
    *Recent episodes of sudden cave-ins include one in 1957 on via Piscicelli in Vomero (and again up in the Vomero hills in Sept,         1967, on via E. Cortese) and on via de Pinedo (at the crossing of via Baronie) in 1964 at Capodichino. Indeed, during an                     inspection of the run-off collector, 22 meters below the above-mentioned via de Pinedo, some manufactured arches were found     at some collapsed points and, also, extraction shafts were found in the overlying incoherent materials.}

Tufo. Extraction was either open-pit or underground. We refer you to the cited classic monograph by Dell’Erba. [trans. note: bibl. ref. 4 in title]
Tunnel [gallery] extraction is the method that is of immediate interest when discussing the subsoil. We note that in ancient times, the tunnels were dug such as to have a flat ceiling and two parabolic walls. The width of the ceiling was kept between 4 to 5 meters; the walls were 10 to 15 meters high, and there was a covered trench. Some examples that still exist are the Cristallini grottos, those along via Vecchia di Capodimonte, those between that road and via Nuova Capodimonte, the Gavoni [grotto] at Piazza Cavour, Piazza Dante, the Ventaglieri, and the Mangone quarry at Virgil’s Tomb. Others along the Porta-DueFontanelle axis were demolished when there was nothing left to extract. Between 1860 and 1870, that method fell into disuse in favor of a faster and more economic one, that of the curved arch. The shaft went in beneath a semi-elliptical or, rarely, semi-circular arch, and the walls were sharply accented parabolas.
These galleries were bigger than the earlier ones and could be as high as 22 meters plus the trench for waste rock. Cutting was done with a tool called a smarra, that is, a pick with two vertical blades at the points. Good results were obtained and the resulting blocks were about 25 centimeters on a side (until 1900 they were about 70 to one meter; the dimensions were then reduced such as to obtain about 100 to a meter).
The new method put hills at risk. Galleries crossed and intersected beneath them, leaving only slender supporting columns at the naves. The need for tuff increased, and gallery extraction continued. Some older galleries were demolished and others were indiscriminately expanded, such as at S. Rocco, Miano, Chiaiano, via Nuova Capodimonte, Connochia, S. Gennaro dei Poveri, Materdei, Fontanelle, Corso Vittorio Emanuele (Parker, Grotte Comola), Mergellina, Fuorigrotta, Posillipo and Pianura.
From 1935 to 1941, there was a crisis in the extraction trade. In the war years of 1941-43, cavities in the city center were used as air-raid shelters; at the same time, extraction continued in those cavities to expand the shelters, themselves. Besides newly dug galleries in the urban center at (Chiatamone, Mergellina), older and unused cisterns were put back into service.
The post-war chaos of 1944 saw this indiscriminate process of extracting tuff pick up again, denuding ancient underground cavities, thinning walls and support columns, and, worse, weakening the vaults. Underground cavities with flat ceilings that are of modest size and that have a 50% ratio of mined out void to remaining supporting pillars of tuff showed no signs of subsoil shifting or slides even 150 years after they were opened. That cannot be said of cavities with curved vaults and that are mined to a greater extent; they show a continuous degradation from separating ceilings and become more dangerous the longer they are open, now approaching 100 years for some of them. Another method of extraction was “bottle” or “bell” extraction, not used in Naples since 1920 but used in the area of Nolano as late as 1957.
The procedure was to sink a shaft, generally circular and uncovered, down to where the tuff started; then, down into the tuff for 4 or 5 meters (which layer would later have a load-bearing function). Then, the shaft was expanded out in a circular fashion to extract the commercial rock and reach the bed. Other similar shafts were sunk nearby, taking care to leave stable layers of support between them. At the bottom, the “bells” or “bottles” were then joined by horizontal shafts. When extraction was finished, the entrance wells would then be sealed by waste rock, in the neck of the bottle, leaving the mined void beneath it.
We have called attention to this method of extraction because there are a number of examples of it in the urban center: via Frullone, via Marianella, and via Chiaia (on the left past the bridge as you move down the street) where there are three wells with their respective “bells” that go from the gardens of the Military Tribunal on top of Monte di Dio almost down to street level. These excavations, thus, go back to a period before via Chiaia was laid as an offshoot of Pizzofalcone
This looting of the subsoil created such dangerous conditions, especially in areas of urban expansion and building on the surface, that state authorities put legal controls on what had been essentially unfettered speculation in the tuff industry. By decree, the High Commission of the Mining Bureau, on 23 April 1926, started to regulate tuff extraction in Naples. The regulation was based on an earlier law from 30 March 1893—i.e. law no. 184, that set up the Mining Police—and a subsequent executive order, no. 152 from 10 Jan 1907 (extended by G. di Stefano). After that, it was necessary to have a license for both open-air and underground extraction of tuff.
In the recent post-war [WWII] period, there was a frenzied hunt for building material. This led to tuff extraction that compromised much of the still green areas in the city (S. Rocco, Marianella, Chiaiano, Posillipo, Pianura). As a result, some single underground quarries were closed in the province and all such quarries were closed in the city ofNaples (drafted by D. Bardi). The regulations allowed only open-pit extraction and only the use of stone-cutting equipment that produced uniform blocks, thus reducing the amount of tuff that would have to be thrown out as waste rock. That was the beginning of the attempts to conserve the integrity of the subsoil beneath the city and, indeed, beneath the green areas that embellish the city.
As for the general situation concerning tuffaceous cavities in the urban center, we have concluded that those cavities with flat ceilings and vertical walls have not degraded over time. On the other hand, those with curved crowns, parabolic walls, and tenuous thinness at the tops, have, indeed, shown clear signs of movement and shifting. Slabs and chunks have chipped off and fallen from the surfaces; support pillars of insufficient thickness have been partially crushed and their bases have sunk into the beds of the cavities (the Chiatamone grotto, largo D. Morelli, the Parker Hotel, the Mergellina grotto, Comola, the grotto of Sermoneta, Posillipo).
Many of the cavities threatened by tuff slides or collapse have been reinforced by retaining walls, tuff columns, bricks, reinforced cement, etc. This has, in some measure, restored the strength of terrain disturbed by ill-advised mining. This has been done in a number of places, including parco del Pino on the Corso Vittorio Emanuele, the grotto at the Parker Hotel, the grotto beneath via Grazio, piazza Sermoneta, piazza S. Luigi a Posillipo, beneath some buildings at Chiatamone, Cappella Vecchia, etc.

         images 39-40 (l&r) Cavity at #59 via
       Montesanto, particulars  of the mouth
       of a well shaft, used as is present-day
       practice, disposing of trash and refuse.

Other cavities, however, have continued to degrade. Their support columns cannot take the weight; they are affected by irregular pressures and even external things such as water infiltration and temperature changes.


We mentioned the “bottle”-type excavation method in order to draw attention to the fact that parts of the city —along the Carmignano [aqueduct] and especially on the slopes of San Martino— are riddled with wells that are similar in construction.Within the city, wells were a source of water and were divided into two categories: passage/isolated; and well springs. We limit ourselves to the first category. These were located along the course of old aqueduct tunnelled waterways. When they were not actually a section of one of the retaining banks of a canal, itself, they were separated from the canal by a separating wall of tuff, one or two meters thick, through which ran a conduit that connected the well to the aqueduct. The second kind, the isolated ones, were on the right side of a canal and were the termination points of that canal. The water from one cistern could overflow into the next one with obvious risk of contamination.
A well has three main parts: the tub or cistern, the bell, and the shaft (see MELISURGO G. Napoli sotterranea, Naples, 1889). The tub is hollowed out of the tuff in the form a prism with a rectangular or square shape with the bottom of the excavation slightly concave or sloped to a particular point for ease of draining and cleaning. The bell is the empty space above the tub; the part of the empty space that corresponds and connects to the covering is more properly called the ciclo, the same name used for the shafts in underground tuff quarries. The ciclo space is shaped like a barrel, sail or tent with four bowed-out cylindrical surfaces. The shaft is the vertical part of the well that connects the tub and bell to the surface or to a building above where water could be drawn from various floors.

image 41

image 42



41, 42, 43  shape and forms of
the Carmignano aqueduct in the
zone beneath via Pesisina.

The shaft of the well could be located centrally as in “bottle” or ”bell” extraction; it could also be off-center or on the side.
Wells have also been found on the Poggioreale hill and in the Materdei section the city.*2
The wells in the Montecalvario section of the city were fed by the Carità canal, which drew its water from the Carmingnano aqueduct beneath the Palazzo Cavalcanti.

The above-mentioned canal, once it reached the spot beneath the corner between via Toledo and via Nunzio (today near Pasquale Scura) sent a branch off to the right to provide water to the wells of buildings to the east of Largo Carità and via S. Liborio as far as the Vacche Parish. The San Liborio steps are the beginning of Vico [small street] della Carità. After that, the main canal turns to the left and reaches a spot beneath Palazzo Cavalcanti, where it gets water from the upper Carmignano canal. After a short stretch, the canal forks; on the right, it forms the Peruso Nuovo branch and, on the left, the Tuvole branch. The former branches again at various points and provides water to the rest of the buildings on vico Carità, as well as to part of the following streets: Formale, v. Splendore, Magnocavallo (via F. Girardi), v. Trucco, v. Campanile, v. Grotta Mastrodatti, v. Consiglio, v. del Gelso, v. Speranzella, v. del Teatro Nuovo, v. Carità as far as [the church of] the Madonna della Grazie, v. Noce, v. Primo and Secondo Concezione Montecalvario, v. Primaportapiccola Montecalvario, part of via S. Maria Ognibene, v. Polito, and the steps of S. Maria del Monte, with the last well in the S. Pasquale convent.}
We repeat some of Melisurgo’s survey notes in order to show the kinds of shifting and movement in the subsoil that occur time and again beneath the buildings along via Formale in the direction of the church of Trinità degli Spagnoli. We note the remarkable sequence of calamities affecting the buildings on vico Noce del Calvario: 1861—Shifting and collapse of the wall on the east side, 5.90 meters from the building at vico Noce 20; 1890—a cave-in affecting buildings at vico Noce 14, 17 and 22 and via Prima Concezione 7; 1963—earth slides at vico Noce 17, 29 and 22; salita Magnocavallo (Girardi) 17 and via Prima Concezione Montecalvario 7.

Core samples done in 1963: vico Noce —a shaft of 28.60 meters reached 12 meters above mean sea-level [MSL]; a second one, 30 meters deep, reached 9 meters above MSL.
The first sample passed through 5 meters of refuse, 2 meters of humus, and then a series of layered pozzolana, sand and alluvial pumice; the second sample found vegetable matter down to 7 meters and then the same alternating mixtures of incoherent terrain.
In the first two periods, various water wells were found that came from the old Carmignano della Carità partition. There were three beneath the building at via Nove 17, one beneath via Noce 20 and one beneath via Nove 20. The last one had a cistern hollowed out of the tuff and a square shaft partially carved into the rock and partially into incoherent materials supported by retaining walls. There was also a rain catchment cistern beneath the staircase at via Noce 22 and another in the building at via Prima Concezione 7.
The banks of earth and cappellaccio [loose, poor quality soil] beneath the foundations of the building at no. 17 rested on the vault that formed the ceiling of an underground cistern that was dug out only 40cm. into the tuff. The foundations, then, of these buildings —some with five stories— rested on incoherent terrain and were no deeper than 4 meters from street level. We note that the sub-foundation work done in 1861 and 1890 did not save the buildings from the cave-ins of 1963.
As we see from reports and our on-site investigations, the strip of land called the “Quartieri,” just a few meters above via Roma is affected by canals, cisterns and basins. The buildings in that area are generally taller than they should be, measured geo-technically, in terms of the resistance afforded by the land the rest on as well as by the strength of the buildings, themselves. If they have not been recently restored or shored up in some fashion, they are at the limits of their stability. We add to the information already given to us by De Stefano (see Chapter IV, part 2) on the presence of underground canals cut into the tuff: i.e. the position of ovoid sections along the minor (horizontal) axis Vi of the major (vertical) axis means that they can have no influence on the phenomenon of cave-ins, nor have we found in the cited literature any mention of that as a cause.
We can’t say the same for the cast-iron street conduits laid for the old Serino aqueduct; they were laid directly into shallow surface trenches. No reinforcement, shoring up or compaction of the loosely compacted soil was done when they were originally laid, nor have such measures been undertaken since, except in particularly dangerous spots.
Such measures could not be put in place at the time of the original installation for economic reasons and, more importantly, because of the urgent need at the time to have a supply of running water in the wake of the cholera epidemic (1884). The conduits of potable water in the older parts of the city are still suffering under the effects of this largely unchanged situation except in those cases where earth slides, the building of new roads, or general urban renewal have, in fact, led to the replacement of the older conduits with newer ones. Even modest pressure on the conduits can cause them to shift and start to leak, leading to erosion in the terrain that supports them as well as in the terrain around the tufo block foundations of nearby buildings. Many of these buildings are very tall, and the terrain that they rest on is compressible. The equilibrium of buildings in this situation is overtaxed and movements in the subsoil can assume alarming proportions.
The sewer system in the urban center is the subject of another part of this report, but we can say that the planning and construction of the system has been carried out efficiently. The base is a bed of hydraulic mortar (Vesuvian pozzolana and slaked lime) of a width never less than 45 cm. The sewage conduit is embedded in that mortar work such that leakage cannot occur except in cases of influence of external factors over a period of years and even decades. Even small factors, however, can cause voids around the conduit and eventually lead to breaks. That can lead to the subsidence of adjacent building and, in turn, can affect the road bed beneath the surface of the streets where thosebuildings are located.
All of these causes are interrelated and, themselves, made potentially worse by the possibility of cave-ins and slides in the terrain due to the number of cavities —some at considerable depth— in the subsoil.  p.117

image 44

image 45

image 46

image 47

Particulars of a huge water storage cistern; the walk-over bridges
are carved from the surrounding tuff (45), cistern water flow control
system at the union of the bridge-canal (44), water stains
indicating various  water levels (46), small overflow channel for
diverting water to an adjacent cistern (47)

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The Subsoil of Naples
Part 2, chapter 4

Distribution of Cavities beneath the Urban Area
under the direction of Eng. Prof. Roberto Di Stefano

The great number of cavities (and their entrances) in the urban area makes it difficult to present an overall view of the subsoil of Naples. It is, thus, helpful to take a look at the various sections of the city and review the chronology of how these cavities have been excavated over time. We do that by examining the urban history of the city. We might then come up with a zone-by-zone picture of the urban subsoil that shows us where the excavations are most intense and where they present the most problems, which is, after all, the object of this entire report.
We can start by looking at figure 50, which presents the urban situation in Naples at the end of the 11th century. It is based on the well-known map published by B. Capasso in 1892,*(1) which, however, limits itself to the area bounded by the old city walls. The map shows the areas of early Greek and Roman settlements located within the walls as well as some roads outside the walls that may be assumed to have existed at the time. We can thus see the connections to the west.
One such road runs through a valley corresponding to today’s via Chiaia, then along the beach to the cripta napolitana [trans note: the ancient Roman tunnel at Mergellina that goes through the Posillipo hill] and then left to the Posillipo coast. The other road, puteolana per colles, starts where one of the decumani [trans. note: east-west streets of the old city] ends, then by Spirito Santo and up via Salvator Rosa to run along the Vomero Hill to Antignano and then down the hill towards Agnano and the Campi Flegrei. *(2) As far as the connections to the north are concerned, we see the Capua road leave the city at Porta Capuana and the road to Nola leave at Porta Nolana.
*{1. Capasso, B. Topografia della Città di Napolinell’XI secolo. Naples 1895.}
*{2. Napoli, M. Napoli greco-romana, Naples 1959, p. 112 and p. 115.}

Another road must have connected Naples with the Vesuvius area (Herculaneum and Pompeii). These roads are amply attested to by archaeological and philological evidence, although there is some uncertainty as to their precise routes. Our goal is simply to present an approximate but fair indication of their presence. In tracing their routes, it was opportune to locate the various Greek and Roman tombs along those paths, knowing that they were situated immediately beyond the city walls and, thus, along the main lines of communication. We thus see the area of Neapolis, founded around 470 BC after the eclipse of the earlier Palepoli, which, under the name of Parthenope, grew up on the Pizzofalcone hill, approximately between 680 and 530 BC.
Clearly, the choice of where to build the settlement of Naples was closely linked to the morphology of the area. The site was surrounded on the east by a marsh, on the north and west by natural trenches that served as canals that gathered water from the surrounding hills, and, finally, on the south by the sea. Again, the city had canals as well as the sea and small hills such as Caponapoli, S. Giovanni Maggiore, Monterone, S. Marcellino, and Sant’Agostino alla Zecca. These natural conditions were such that the area could be easily defended by the simple addition of a city wall. From the period of its founding (470 BC) until 1140, the year that marked the end of the Duchy of Naples, the city wall underwent four expansions. *(3)
*{3. i.e. after the original wall from the 5th century BC, there followed another in the first half of the 4th century BC; and then in the 5th, 6th and 11th centuries AD.} In the 11th century, Naples had around 30-40,000 inhabitants, not having grown notably since Roman times. It had a relatively modest building density.
We attribute a first group of cavities to this period.*(4) We note that there is evidence of digging in the subsoil of Naples from as long ago as 5,400 years. This is shown from the discovery in 1950 of two so-called “oven” tombs [trans. note: alias Chalcolithic and Copper Age] in the Materdei area. They were at a depth of about 6 meters “dug into the tuff wall of a slight slope and consisting of a small chamber with access by means of narrow corridor.” *(5)

48. Greco-Roman Naples (after B. Capasso)                                                                            49. XI Century Naples (after B. Capasso)

Among the most ancient excavations we also find the grottos at the foot of Mt. Echia, in the area of Santa Lucia and today’s via Chiatamone (the Platomonie grottos).(6) At the end of via Chiatamone we find the large cavity once held to be the Cave of Mithra; access is from the area behind the church of Santa Maria a Cappella Vecchia. There is another ancient grotto in the Posillipo hill with an entrance in at Piedigrotta near what is called “Virgil’s Tomb.” (7) This is actually a tunnel, 700 meters long, 4.50 m. wide, and 5 m. high on average. It is said to have been dug in the age of Augustus by the architect Lucius Cocceius Auctus and which even by the time of Seneca was dark and dusty. It was restored and enlarged numerous times by lowering the road bed. It was subject to cave-ins, especially after such lowering. It was finally abandoned in the 19th century.

Besides these, there is another tunnel in the Posillipo hill, built at the behest of Lucius Aelius Seianus, perhaps by the same architect, Cocceius Auctus. Also, the Posillipo hill was traversed by the Claudiusaqueduct,*(8) from Roman times, built to carry water from the Serino aqueduct to villas at Posillipo and Bagnoli, and most importantly to the military naval center at Bacoli and Miseno.
We don’t have enough technical information to trace the path of this first aqueduct, but from extant descriptions, it must have been: Ponti Rossi, S. Eframo, the Botanical Gardens, and the Costantinopli Gate,forking there, perhaps to guarantee a water supply into the city. Then, it went to Gesù e Maria, S. Elmo, Vomero, and the ancient Pozzuoli grotto. From there, the main conduit went towards Mt. Olibano, Pozzuoli, Bacoli and Miseno, and a secondary line went towards the Posillipo point. In any event, it is certain that in these days of urban life, the inhabitants of Naples drew water from existing rivers (Sebeto and Robeolo) and from springs. It was not until later that they had access to the Bolla aqueduct.
Chiarini, in his comments on Celano, is of the opinion that the Claudius aqueduct must have co-existed with the Bolla aqueduct, the construction of which he attributes to the Romans, and perhaps eventhe Greeks. (This contradicts those who hold that the Bolla aqueduct did not exist until the 12th century.) Chiarini says that the Bolla aqueduct served the city by carrying water from the Volla plain (also Bolla and Polla) to the lower sections of the ancient Greco-Roman city.
To support his view, Chiarini points out that Naples, a city with water and public baths, existed before the construction of the Claudius aqueduct. Indeed, when Belisarius destroyed the Claudius aqueduct in 537 AD after using the conduit, itself, to get into the city, the citizenry really did not suffer at all since they still had access to water from the underground Bolla aqueduct.
Also, certain stretches of the Bolla aqueduct in the urban area have opus reticulatum brick work and marble covering.*(9)
*{8. see Colonna, F. Scoperta di antichità in Napoli, 1898, from which p. 67: [ref to November 1882] “...during construction on the tunnel for the new Naples-Pozzuolisteam tram, an ancient aqueduct was found that could only be partially explored since it was not totally uncovered.” An accurate description follows.}
*{9. see Celano-Chiarini. Notizie del bello, dell’antico e del curioso della città di Napoli, vol. II (1870 edition) pp. 404 and following. Chiarini specifies that three stretches of the canal were carved completely out of a bank of tuff and that, furthermore, “...beneath the street dei Tribunali...” [trans. note: the central eastwest road of the ancient city] the canal was partially covered with “pieces of marble,” most notable of which included “...a white marble statue lying on its side with the knee visible and the folds of a gown, visible from the breast to the knee; also, a piece of a Corinthian cornice and the remains of a column. The other pieces were crumbled but might be from something on the opposite side and not visible.”}

Thus, it is plausible to hold that in the 11th century, a first part of the Bolla aqueduct was already in existence.
The other hill containing some of the most ancient cavities is the Capodimonte hill. We presume, it was there that they extracted the necessary tuff to build the Greco-Roman city wall, then movimg the tuff into place via the natural valleys of the Vergini and Sanità.*(10)
There were also Christian cemeteries in the same area. There is a vast literature about them, but it is still an open question if these cemeteries were placed in cavities that already existed or if —in keeping with the burial traditions of ancient peoples— they were purposely built underground by Christians for their saints and martyrs and then later expanded in order to let the faithful be buried near the objects of their veneration. A number of catacombs came into existence in this fashion: S. Gennaro dei Poveri (3rd century), S. Vito or S. Maria della vita (2nd cent.), S. Gaudioso or S. Maria della Sanità (5th cent.), S. Severo (end of 4th and start of 5th cent.), and, in other areas, S. Eframo Vecchio (end of 3rd cent.), S. Maria del Pianto and the catacomb beneath S. Martino monastery. The main reason, however, for the excavation of cavities was to extract stone for construction (tuff, lapillo, pozzolana, etc.) *(11) which is why the increase in the number of cavities is directly proportional to thegrowth of the city.
Let’s look at a detail of the Lafrery map (fig. 53) now, some five centuries after the map was made (1566). It is the oldest map we have, drawn up when the places it represents existed, and it is considered a very reliable document. It shows in a “bird’s eye” perspective (not flat) the city and immediate environs beyond thewalls created by viceroy Don Pedro di Toledo between 1533 and 1574.
*{10. An interesting treatment of the excavation of tufo and other construction materials in Naples in the past is by G.B. Chiarini in his comments on Celano. See Celano-Chiarini, op. cit., vol. I (1870 edition) pp. 87 and following. Also see Carletti, N. La regione abbruciata della Campagna felice, Naples, 1787, p. 47.}
*{11. See Chapter III, part II of this report.}
*{12. Colonna, F. op cit, p. 13, contains the contract for the building of these walls. Among the stipulations are that the tuff for some portions of the wall was to mined from the Chiatamone hill.

After the Duchy of Naples, in the Norman period, there was no urban expansion of Naples. That had to wait for the Angevin period when Naples became the capital of the Kingdom. It was a time of development and urban renewal that saw the population increase from 40,000 to 60,000. When the Aragonese arrived in 1442, Naples reached a position of prominence from both an economic as well as an artistic point ofview. The beautiful tavola Strozzi [trans. note: an oil-on-wood painting of Naples from c. 1472] gives us an idea of the magnificence of the city during the Aragonese period. In 1484, work started on the new Aragonese walls to extend the city to the south, east and west. Many sections of those walls and towers can still be seen today. Within the city, at the same time, many smaller dwellings, numerous larger ones for the patrician class, as well as churches, convents and monasteries were built.
The work of urban expansion and renewal was then carried forward under the [Spanish] Vice-realm, primarily by Don Pedro de Toledo, who, as we have said, undertook to expand the city walls. This expansion of the walls, which would be the last, was the largest in the history of Naples. It was primarily of a military nature and was the first phase of a vast program to put order into the entire layout of the city by paving the principal existing roads and building new ones, includingvia di Chiaia. *(13)
Among the new roads, the most notable one was undoubtedly via Toledo (today, via Roma), built by Don Pedro along the old Aragonese trench from the Royal Palace to Porta Regia. Along this road, that is, at the foot of the Vomero hill, there arose an urban nucleus (indeed, called the “Spanish Quarters”) originally destined to garrison troops and then taken over by the civilian population. This was the period when many in the upper classes decided to move their dwellings to the new road closer to the Royal Palace, thus leaving their homes in theolder parts of the city, which were then rapidly and almost completelytaken over by the poorer classes. There was then a rapid decline in the urban fabric in this part of the city. It was caused largely by the chaotic increase in the construction of tall (and overly tall) structures and the building on spaces that had been open and green.*(14)

*{13. The road was built between 1559 and 1634 to a plan by Domenico Fontana. It insured a better connection with the beach area of the city than the traditional longer route along Chiatamone and was less exposed to the sun and wind. See Celano, C., op. cit. vol. 5, pp. 562 and following.}
*{14. See Parrino, D. A. Teatro eroico e politico de governi dei vicerè del regno di Napoli, cited here from the 1875 edition, vol. I, p. 38 (the first edition is from 1692): “...The dwellings of the citizens are quite comfortable and tall; some are even six and seven stories. This is possbile because of the light weight of the stone and the fine quality of the sand, called Pozzolana, that, mixed with lime, makes a perfectmortar.”}
The possibilities offered by various life styles—even modest ones—,the presence of the vice-royal court and a large noble class as well as economic incentives all contributed to a notable increase in thenumber of persons coming into Naples, bringing the population to 212,000 in 1547.

New excavations were opened in order to meet the increasing demand for construction stone. This happened primarily on the Capodimonte hill, already cited, which provided easy access into the city along the Cristallini valley and the valleys of the Vergini and Sanità to the San Gennaro Gate and the oldest parts of the city. However, in order to serve, the zones of expansion to the west of the ancient walls and all the way to via Toledo, it was easier to extract stone from the area of S. Lucia al Monte and Ventaglieri, and then to use the easier access at the Medina Gate.*(15)
The cavities to build the “Spanish Quarters” were opened on the eastern side of the hill, the part that runs from Petraio, then by S. Carlo to Mortelle and Pizzofalcone. This was the period when the technique of subsoil excavation finally developed such as to permit extracting materials on the site, itself,  of buildings that were going up. That technique was used primarily in the case of very large buildings such as churches and monasteries *(16) and a technique that then expanded greatly over the course of the next two centuries. In these centuries (i.e. the 1500s and 1600s) the city found itself in the absurd position of facing a growing population (to 500,000 in 1700) and, at the same, a series of “pragmatic” laws that opposed any building outside of the city walls. This was for military and economic reasons, but without any coherent economic policy.

*{15. The assault on the San Martino (Vomero) hill was so intense —at the end of the 16th century and beginning of the 17th— that viceroy Count di Miranda issued an official ban (20 May 1588); there was another such ban issued by Count di Lemos (9 Oct. 1615) in which all excavations were banned, whether to extract stone or to put up new buildings.}

*{16. For example, the monastery of S. Gregorio Armeno, those on the Pontecorvo slope and the Gerolamini monastery. See chapter 3 for a description of the “bell” or “bottle” excavation technique. Note also that Carletti (among others) writes (Topografia universale della città di Napoli, 1776, p. 9): [tuff] “ used for building and is cut from beneath the present layout of the city and from the surrounding hills.”}

As a result, building within the city increased chaotically and unpredictably, and even spread outside the city walls in spite of the official bans on such construction. It spread along preexisting roads, wherever possible, but always without even the most elementary urban planning. Such a plan was even lacking in 1717, when a decree was issued that removed the building ban. [trans. note: That year marked the beginning of the 20-year Autrian vice-realm of Naples in the wake of the Wars of the Spanish Succession.]

The layout of Naples in the 18th century is given to us with great precision in the map drawn up by the Duke of Noja, Giovanni Carafa, finished by Niccolo Carletti, who published it in 1776 with comments and annotations.*(17) The map shows the most important transformations of the city during the first 40 years of the Bourbon monarchy. This was when the city was once again the capital of a kingdom and enriched itself through important public works. The city walls and many city gates were demolished, construction was begun on the Royal palace at Capodimonte as well
as the Foro Carolino and the Hospice for the Poor; streets were put in order and many new private dwellings added to the wealth of buildings in the city.

Obviously, a great amount of building material was needed to accommodate construction of the previous two centuries. The urban area was not much larger than what is shown in fig. 53 (i.e. more or less the same city area as in the 1500s). The material for all of that construction came basically from the same zones shown in fig. 56; that is, from the hills of Capodimonte and Vomero, from the sides facing the sea. Thus we have intense excavations in Vergini, Cristallini, Sanità, the S. Antonio slope up to Capodimonte and lower down almost to via Foria. New cavities were opened at Montesanto, Ventaglieri, at S. Antonio ai Monti and in the strip above the Spanish Quarters reaching up to about where the street, Corso Vittorio Emanuele, runs today.

The expansion of building along the Chiaia beach led to excavations on the western side of the hill of S. Carlo alle Mortelle as well as in the Mergellina area. At the same time, there was notable development in the techniques of excavating on site, that is, beneath the very spotwhere a new building was to rise. That method was so abused that in 1781 it was forbidden, and excavating beneath and inhabited area waspunishable by a three-year prison sentence, all in an attempt to stem the tide of cave-ins that were occurring. *(18)

*{17. Carletti, N. Topografia universale della città di Napoli in Campagna felice,
Naples, 1776. op. cit.}

*{18. That decree is contained in annals of the Tribunale di Fortificazioni of 3 Oct 1781. The text has been published by Strazzullo, F. Prammatiche per l’ediliza napoletana dal’500 al ‘700 in “Ingegneri” n. 36, 1966, p. 46 (capo IV)}

image 54  Plan by Stophendal (XVII century

image 55
Plan by Giovanni Carafa, Duke of Noja (XVIII century)
These often occurred because of the presence in the subsoil of the various conduits of the Bolla aqueduct, which had grown with the city. As we have said, with the population growth at the beginning of the 17th century, the need for water increased. Putting the old Claudius aqueduct back in service would have cost two million ducats, a financial impossibility. Thus, a plan was approved in 1627, a plan by the nobleman Cesare Carmigano and the mathematician, Alessandro Ciminelli, in which they offered, at their own expense, to bring water to Naples from the Faenza river. The work was completed in under two years in spite of great difficulties. On 29 May 1629, water entered the city and was channeled into the conduits beneath via Foria, via delle Pigne, the university and via Toledo, at first as far as the street at the Garrese Gate and then, after 1631, to via Conte di Mola.
In 1753, king Charles of Bourbon acquired the waters of the Pizzo river, a tributary of the Faenza, in order to supply the fountain-falls at the Caserta Palace. (The Faenza, as we have noted, fed the Carmignao aqueduct.) As a result, there was a drop in water supplied to the city. Thus, in 1770, as Carletti notes, king Ferdinand IV of Naples, decreed that water passing through the fountains at Caserta would then be channeled to Naples and into the Carmingnano conduit. That increased the supply but not enough to satisfy the entire population. Indeed, as Chiarini points out, that water flowed 26 mills on privateproperty, the millstones of 4 city-owned properties, 9 industrial factories, numerous private concessions, and 32 public fountains.

At first, the people, could at first only use the fountains fed by the Bolla aqueduct since those fed by the Carmignano were ornamental *(19) and only after some effort were they finally channeled into public wells. If we consider the amounts of water used by small urban industries (dye-works, tanneries, bath houses. etc. ) and water supplied to the many monasteries (“in abundance”), we see why many persons had only springs and public fountains for their water supply. Furthermore, the hill areas (Capodimonte, Vomero, Posillipo) had no aqueduct conduits at all and had to rely on the rainwater they could collect in reservoirs and cisterns. It was only in 1885 that the modern Serino aqueduct as built.
*{19. They were surrounded by gates to keep the populace from the water.}

Before looking at the situation in Naples at that later date, however, we consider the last stages of urban development and excavations in the final decades of the last century.
In the long period of Bourbon rule, public works were carried out that are still relevant today. These include the reordering of the area along via Costantinopoli and the construction of the important road, Corso Maria Teresa [trans. note: today’s Corso Vittorio Emanuele], which runs halfway up and along the Vomero hill for 5 km from Piedigrotta to the Cesarea [church]. We also note public works under the decade of French rule (1806-1815) during which time the road, Corso Napoleone, was built from the museum up to Capodimonte; also, the area around via Foria was reordered, via Posillipo was extended all the way to Coroglio, and the Botanical Gardens were built.
The Bourbon period corresponds to the beginnings of the industrial revolution and the first plants and factories as well as early railways and steamships. That substantial growth in public works, however, did not translate into any bettering in the economic or social lives of the ever increasing population. The people were crowded into old housing in terrible conditions of overcrowding and poverty. It was not until after the unification of Italy that attempts at planned urban renewal were made, which we see in in the early failed undertaking by the Banca Tibertina in the Vomero area. As well, we see the renewal of the Chiaia area, extending it towards the sea with the new road, via Caracciolo, and the expansion of the entire seaside area with new roads such as via Vittoria Colonna and Parco Margherita. Also, we see the expansion of the area of Vasto and the projects of the Risanamento corporation, such as the new Corso Umberto boulevard running between the train station and the stock exchange. These projects. however, did not bring any real benefits since they were isolated episodes and not part of an overall plan of urban development. In any event, such a vast complex of public works required additional excavations; these were, naturally, done outside of the urban area, which had and overtaken earlier excavation sites (fig. 60).

There are other cavities from the 19th century in the Capodimonte hill,
and more to the north in the Scudillo area, in S. Rocco, the Fontanelle, and on the northern side of the Materdei and Vomero hills. A final increase is shown along Chiaia and along the path of Corso Maria Teresa, and there are a few totally isolated cavities at the summit of the Vomero hill. Finally, we note the construction between 1882 and 1885 of another excavation, 734 meters long, in the Posillipo hill. It showed severe cracks after just a few years; they could not be repaired and the site was abandoned. Another, smaller gallery was built next to it. It fared no better when an inappropriately slender tuff column was crushed, causing a collapse.

As early as 1855, the city deliberated on a tunnel to connect S. Francesco di Paola to Largo Cappella. It was started and suspended after progressing a distance of “1200 palms” [trans. note: about 300 meters.] It was only later, in 1927-29, that the Galleria della Vittoria was built. It was 624 meters long and connected via Cesareo Console with via Chiatamone.  Finally, we note the four cable-car tunnels: Central, Montesanto, Chiaia and Mergellina. The urban expansion of Naples from the end of the 1800s to today has been extremely intense. It was at first modest, disciplined and carried out in the areas we have mentioned (Vomero, Vasto, S. Lucia, theChiaia quarter) and beyond the Posillipo hill towards Fuorigrotta.

image 58

image 59

image 60

58. Entrance to Laziale tunnel at Piedigrotta            59. Entrance SEPSA rail tunnel at Montesanto
              60. Entrance to galleria of Victory, via Acton
  SEPSA (Società per l'Esercizio di Pubblici Servizi Anonima) was a public transport corporation that ran the two
narrow gauge railways in Naples, the Cumana and the Circumvesuviana lines until it it was consolidated with other transport corporations in 2012. And the pressing question, in #60 the Victory Tunnel -- what Victory are are they talking about? You'll never guess. First correct answer wins a free ride on that train in #59.
After the ravages of war, however, the city underwent a rapid and intense expansion to meet the needs of a population that had grown to 1,200,000 persons. Unfortunately, there were no precise plans or appropriate building codes this time, either, and the expansion was disorderly and chaotic. As for the digging of new quarries for building material, they were ever farther from the urban center: along the Posillipo hill above the new road, and some in the areas of Colli Aminei, Scudillo, and the Cangiani Chapel. Large cavities and long conduits have been built since 1885 in order to provide reservoirs and conduits for the Serino aqueduct.
To the vast collection of cavities that we have indicated so far, we add the intricate web of conduits, large and small, that make up the sewer system *(20) and the ancient and modern aqueducts that we have mentioned. They run at various levels, often crossing and intersectingin the oldest parts of the city. We can postpone until chapters 5, 7 and 8 a more detailed discussion of the topic, but we point out that the illustration gives only an idea of the intricate complex of conduits and canals. To those we must also add the many wells that in the past served to provide spring water.*(21)
*{20. From historical sources, we know that, in ancient times, the sewer consisted of a large canal, about 5.30 x 3.70 meters, that left from Piazza della Pignasecca. Carletti says: “this work, popularly called the ‘chiavicone’, winds along Toledo and picks up rain water at various points from the many streets and alleys that come down from Mt. Echia and Mt. Ermico to the Castel dell’Ovo, the Vittoria and the Chiaia beach.” Carletti, N. op. cit. p. 263.}
*{21. Lambertini writes (Lambertini, D. "Acquee sotterranee nel’ambito del centro urbano della città di Napoli" in Boll. della soc. natur in Napoli, vol. LXIX, 1960, p. 226): “In some cases, underground water rises and flows out on the surface in the form of true springs, known and used in the past, such as those that emptied along the beach line where it slopes towards the sea (Piazza Francese, S. Pietro Martire, Mergellina, S. Lucia, etc.) These springs, all of modest size, have disappeared today due to the changes in these area caused by construction...”  We can put off to chapter 5 the details having to do with water supply. We do note here, however, the thermals springs of Chiatamone and S. Lucia, where sources exist within Mt. Echia that still produce mineral water for drinking and hot water for therapeutic baths that for many years have been a commercial source of income. The wells marked on the map are listed in the appendix. For the schematic of the Bolla and Carnigano aqueducts, we have followed the description contained in Melisurgo, G: Napoli sotterranea, topograifica della rete di canali d’acqua profonda, Naples 1889.}

Having now followed the development of cavities in relation to urban growth, we can group these cavities by zone within the city.*(22)
*{22. See table III in the attached atlas.}
They are:
    a) The area of the ancient historic center, bounded by via Roma until the National Museum, then via Foria, via         Cesare Rossaroll, S. Antonio Abate, via Pietro Colletta, the “Rettifilo” [Corso Umberto], and PiazzaCarità;
        b) Vergini and Sanità, the areas of the most intense excavation, extending from above via Foria to the Capodimonte         Palace and from the eastern slope of the Miradois hill to the western slope of the Materdei hill;

        c) the slope of the Vomero hill, above the street that runs from the Spirito Santo [church] by Piazza Dante to the             National Museum. Thezones included are Pontecorvo, Montesanto, Ventaglieri until beyondthe Corso Vittorio                     Emanuele;

        d) the eastern part of the Mortelle hill, above the “Spanish Quarters;

        e) below Mt. Echia in the low area formed by via Chaitamone, via S. Lucia and via Chiaia; *(23) [footnote 23 is                 missing]

        f) the western side of the Mortelle hill and part of the sloped of the Vomero hill that faces the sea;

        g) the northern area of Vomero, from Materdei to Scudillo;

        h) Posillipo (including the area covered by the SPEME convention) to Mergellina, the area in back of the railway                 station; there are here, as well, a limited
—but well-known— number of grottos with entrances from street level as         well as, along the Posillipo coast, sea-grottos often used to store boats;

        i) the strip in the northern areas, outside the urban center, covering the areas from S. Rocco di Capodimonte, and             the Cangiani chapel to Chiaiano and Marano, that is, outside the Naples city limits.

Outside of these cavities in these areas, except in isolated cases, or something to do with the surface network of small pipes in the aqueducts or sewers, it is not probable there are other cavities that might affect the subsoil of Naples.
Our reasoning here has been to reduce the area where we have to find and identify cavities. Through that simplification, we may be able to wind up with a rational picture of the distribution of these tunnels and cavities and thus help solve two important problems: urban planning according to the “spessore” model and guaranteeing the stability of buildings. [translator's note: "spessore" means thickness. Essentially, worry about the large quarries first.]

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The Subsoil of Naples
Underground Waters

under the direction of Eng. Prof. Carlo Viparelli

1) Premise

1-1) Given the various types of terrain in the subsoil of Naples and the surrounding area, we focus on the overall complex of the terrain and on the physical extent of a given terrain type, how one alternates one another, and how all of that affects the circulation of underground waters as a whole. We take this approach, rather than concentrate, one by one, on terrain type or water source.
In looking at the various subsoil types in Naples and the area, we can distinguish: environment A, dominated by tuffaceous lithoid materials, spread in banks of notable thickness and extent, broken only by fractures, stratification junctures, or by patches where tuff cementation, for whatever reason, never occurred or remained incomplete.environment B, dominated by loose materials, the characteristics of which may vary greatly; they alternate frequently in strata or pockets of limited thickness and may contain fragments of tuff strata or modest areas of lava flow. In environment A, given the reduced permeability of tuff, the water that filters through such a mass is quite small even with a steep hydraulic gradient [flow]. Vice versa, in zones not saturated with water, active water circulation stabilizes by percolation through the mass of tuff, whether through cracks and non-cemented strata that here and there interrupt the continuity of the formation, or along contact surfaces with other stratifications, or, finally, through cavities opened over the centuries by man. In environment B, as noted, the mass is extremely mixed, with alternating terrain types of different degrees of permeability both vertically and horizontally. In any event, water finds ways to penetrate into such terrain and filter through it. Such terrain is a filter with a permeability that may vary from spot to spot, but that allows water to pass through even with a modest hydraulic gradient.

We are concerned here only with the various ways in which water can circulate in one environment or the other, thus, in discussing environment A, we shall not distinguish tuff by age or differentcharacteristics. Indeed, in talking about type A terrain, we include even that which is interrupted by other strata or pockets and the patches where the tuff cementation has not occurred or is incomplete.

Likewise, in discussing environment B, we make no distinction among various types of sedimentary materials; they may be marine or lake or have been deposited at various times in relation to the various Flegrean or Vesuvian eruptive cycles or have been disturbed or moved by atmospheric or human activity or may include fragments of tuff strata and modest lava flow mixed in with it.

On the basis of these criteria, when we refer to the urban center weshall distinguish only where there are surface outcroppings of tuff, resulting in a situation of type A on top of type B and, since the tuff has risen from some depth to reach the surface, a situation, really, of type A at the top, then type B below it, then type A again and then type B below that. We shall, however, not make distinctions among situations found in the industrial eastern part of the city and those in the north on the extended plain of the Terra di Lavoro [trans. note: an archaic term for the area to the north of Naples, centering, approximately on Capua and Caserta] or in the extreme west on thestrip to the left of the Regi Lagni [trans. note: a network of artificial canals in the provinces of Naples, Caserta and Benevento. Total length
is 56 km spread over a basin of about 1000 km2].

As to the depth of terrain of interest to us because the presence of wells, past studies show that those are all in type B terrain. The situation is somewhat different in the area just to the west of the city, on the slopes of the Flegrean hills. There you have type A materials at some depth with, however, small patches of type B on top of it. 1-2) By way of example, in figure 63 we see some traces (and in figures 64 and 70, in more detail) of seven sections of subsoil in the urban center and industrial zone more or less parallel to the coast line. In each section, besides the indication of thickness of both A and B type terrains, we have shown the elevations of some wells drilled in the past that have struck a groundwater aquifer that provided not only water in the aquifer but water that flowed into it as result of drilling. As we see, the lithoid tuff that we have labeled type A terrain, always present within the urban center, gradually decreases in thickness as it approaches the eastern areas and practically disappears east of the Sebeto. In turn, type B terrain within the city is either on top of or beneath type A terrain, but takes over the section completely
once east of the Sebeto. [Trans note: the five ground water/aquifer drill charts below show the wide variety of type A & B areas across the city]

On the other hand, from the same figures, we see that where type A terrain appears, the depths at which usable groundwater is found is actually outside type A terrain and in type B but the aquifer remains usable whether it rests on tufo or is below it. Within the urban center, once the surfaces of the roof and base of the tuff is identified, those surfaces are assumed to be, respectively, the upper and lower surface limits of the zone, the former the surface limit and the latter the depth limit, in which we find usable water. Surface limits like that do not exist once we move to the eastern industrial area. As we see in figures 64 and 70, given that there is only type B terrain, the amount of usable groundwater varies from one vertical section to the next. Our conclusions differ considerably from those of Ruggiero [411] (1) and of others who have since relied on his conclusions.

Indeed, Ruggiero, who had much less data at his disposal than we have today, (see table V,) is of the opinion that in the urban center and industrial areas there are more distinct aquifers in the deep subsoil and that they vary from one to other according to a contour that he calls “eidipsometric”. (figures 71-73) [an English translation for “eidipsometric” is not readily found but as here used indicates a form of isometric data plotting] . More precisely, according to Ruggiero’sinterpretation, two of these aquifers —the second and third ones— are found in the subsoil of both the urban center and the industrial zone; the first one, however, is closer to the surface and found only in theindustrial zone.
From what have observed, however, the series of the eidipsometric curves furnished by Ruggioero refer only to the urban center and, by his own definition, refer only to the second aquifer. Indeed, as we see in figures 74 and 75, within the urban center those curves represent the contour of the surface at the base of the tuff mass and tell us that where type A terrain is on top of type B, we have to go below the tuff to find aquifers with a usable potential.
In effect, type B terrain occupies the entire well area in the eastern zone, and Ruggiero shows a scheme of distinct artesian aquifers moving through continuous strata of greater permeability that are among practically impermeable strata. Ruggiero’s scheme doesn’t seem to fit. It is more correct to use a scheme of a single phreatic aquifer [trans. note: “phreatic” refers to the violent activity produced by hot lava coming into contact with cold water] in which water moves through the heterogeneous mass and preferentially chooses a path through the materials that are more permeable and that are interlaced and chaotically mixed but in direct and continuous communication with one another.

For the same reasons, when type B terrain is below type A terrain, the aquifers are connected. Rather than viewing them as distinct and separate artesian aquifers, they should be considered a single one. Likewise, in some areas of the urban center, water circulates through type B terrain of varying degrees of thickness found both above andbelow type B terrain.This, too, should be viewed as a single phreatic aquifer. The many fractures in type A terrain, indeed, serve to stabilize communication between the phreatic aquifer in the overlying type B terrain and the artesian aquifer within the type B terrain below, such that it is not even necessary to make a distinction between the two.

That can seen from the fact that during various phases of drilling, all authors writing about this, with some rare exceptions, have noted that waters coming up separately from various depths have settled at thesame level.
That is to say, the aquifers along the same vertical section in undisturbed strata of different depths all have the same piezometric quotient, which is to say that they are connected. With that in mind, in discussing individual zones of the city andenvirons, we shall speak of a single aquifer and of surface levels within that single aquifer. More precisely, we shall refer to the level that water rises to from any depth in a well drilled at a given point in an undisturbed aquifer and define piezometric surfaces or surface levels in the aquifer as that surface that at all points has a quotient equal to the piezometric quotient in the vertical section passing through that point.

Beneath the surface level of the aquifer, the mass is saturated with water at all points. Above, it may still be saturated because of the thickness of the capillary fringe, and experience teaches us that the fringe may be some meters thick. In any case, by definition the surface level of the aquifer represents the isopiezic surface with pressure equal to the atmospheric pressure, and in the underlying mass the sinking of individual points below that will give the measure
in a water column of the neutral pressure at that point.

It is also helpful to remember that in situations where we may speak of a single phreatic aquifer, if there are wells nearby, and one of them extracts notable amounts of water from the aquifer, even depressing the level some meters, the water level in surrounding wells will not vary appreciably as long as they are a few tens of meters distant [385] [472]. This confirms what we said about how water moves in type B terrain. This also tells us that within a short distance from the point of extraction you can have notable variations in the level in the aquifer and in the distribution of neutral pressure in the subsoil, but only if the hydraulic equilibrium is disturbed by prolonged pumping and extraction of water from the aquifer in amounts substantially greater than the amount that flows into it from the basin that feeds it.

Before closing this brief premise, we call attention to the fact that in type A terrain above the surface level of an aquifer and above the overlying strip occupied by the capillary fringe, there can still be pockets or strata that are completely full of water. This can happen in a mass where the process of cementation of pyroclastic materials that originally formed the surrounding tuff has slowed or has not occurred at all [241] [338]. Also, since the tuff roof is a somewhat smoother copy of the primitive form of the terrain where it was deposited, such pockets or strata can also occur around the edges of the mass where there are openings that fill up with type B terrain and where surface water tends to infiltrate and accumulate [241] [384].

2) Our Data

    2-1) Early discussions of aquifers in the area include attempts by Celano, Carletti [77], Abate [6] [11] and Sasso [420]. From the presence of spring water on the eastern edge of the urban center of Naples they reconstructed the planimetric contour of the old Sebeto [river]. Those discussions were somewhat far-fetched. We note, however, that as early as 1843 Cangiano [62] [70],
foresaw the possibility, (eventually only partially confirmed) — that the area might hold an abundant hydaulic stratum. That observation was on the basis of a simple geological inspection of the surface and the morphological characteristics of the area.

The stratum would be fed by the chain of calcareous mountains that run from near Caserta to Nola and the Sorrentine peninsula to form an amphitheater around the extended plain of the Terra di Lavoro [trans. note: archaic term for much of today’s Campania region] (Table IV). On the basis of Cangiano’s conclusions —and with Cangiano, himself, as
the driving force behind the project— two wells were drilled at the Royal Palace and at Piazza Vittoria. They were started in 1859 and reached, respectively, 456 and 281 meters. It was on the example of these first two wells that many others were then drilled in the urban center and environs at the end of the last century and beginning of
this one.

With the construction of these wells, we may well say that the firststeps were taken towards a more precise interpretation of the underground hydrography of the area. Indeed, at the end of the last century, there were attempts to interpret data from individual wells [267] [149] [347] as well as, by Palmieri's side-by-side comparisons of data from different wells and, finally, by Cesare [96] in the first essay on the underground hydrography of the area of Vesuvius to the immediate east of the city. There were also attempts during this same period to trace the origins of the waters on the basis of their chemical composition [84] [85].

Another notable step towards understanding the underground hydrography of the urban center and surrounding area was taken in the last twenty years of the 1900s first by engineer Contarino [114] and then D’Amelio [144]. They measured the water level in a substantial number of wells within the urban center and came up with a fair approximation of the contour of the surface level of the aquifer in 1884. Those were Contarino’s first measurements, of about 180 wells.
His second measurements of about 130 wells were in 1889-90 . Also, D’Amelio’s made measurements on about 100 wells) in 1900-01.

As a result, we now know about the levels in the aquifer within the urban center; they may be seen from the curve in Table 5. Then, from D’Amelio’s 1901 measurement, it was also possible to gauge the seasonal variations that the aquifer undergoes throughout the year as well as the mean variations between 1884 and 1889-90, immediately after the Serino aqueduct went into service, and in the following decade, between 1890 and 1901 (see fig. 76-79). There is less information on the levels in the aquifer at the end of the last century in the western part of the city. What we have comes from studies done at the time by the Municipal Technical Office to trace the Cuma effluent. [463].

All in all, whatever the results, we can say that by the end of the 1800s we knew what steps we would have to take to have a more exact knowledge of the hydrography of the subsoil of the city:
We would need accurate and systematic measurement of underground water levels and levels in the aquifer; we would have to reconstruct the geology of the area using stratigraphy from wells and core samples in addition to surface inspection; and we would have to determine the chemical composition and compare waters extracted from the aquifer in various zones and at various depths.

2-2) Studies were undertaken, if not always methodically, in the years before WWII. Thus, in 1926, Fiorelli [206] took accurate measurements of the water levels reached at various times during the year within the many
phreatic wells dug for irrigation in the eastern parts of the city

As well, the Italian Hydrographic Service recorded the daily water levels at some wells in nearby rural areas. (see, for example, figures 81-84). Their work, however, did not give us new information on the circulationof water in the increasing number of wells dug in the eastern part ofthe city to provide for growing industry, or information from core samples in those areas or in the center of the city where urban renewal was pushing ahead ever more intensely. In some —but not all— cases, the data on wells drilled to find water indicate the point in the aquifer where water was found [239] [242] [173] [289]. For core samples, however, even that information is missing. Furthermore, even where the water level is indicated, it is in relation to ground level without, however, specifying the elevation of that ground level and sometimes without even specifying the precise location of the well or core sample.

We can say that the most interesting information about the contour of the aquifer comes to us almost by accident from Guadagno in his report on the geology of Mt. Echia [243] and on the excavations done for the Direttissima [train tunnel]. As for as the western zone of the city, we still have no additional information other than that already cited, i.e. from Varriale’s report on tracing the effluent at Cuma. On the other hand, the many wells and cores samples drilled in this period have given us valuable information on the nature of the subsoil. After that period, D’Erasmo’s study [173] from 1931 was based on all available data and was the first comprehensive geological study of the Campania region; as well, Guadagno, already cited [241] [243], with others from the same period [244], concentrated on the details of the subsoil within the urban center. Rebuffat [397], in the same period, contributed to our knowledge of the chemical composition of the waters by providing chemical analyses of 14 wells.

2-3) It is, however, only after the last war that we have made systematic in which hydrologic measurements, geologic studies and chemical analyses of the waters come together with the help of accurate topographical surveys to provide an accurate contour of the underground aquifer. That work was done under the auspices of the General Cosortium for the Reclamation of the Lower Volturno and was
financed by the Cassa del Mezzogiorno.

Unfortunately, that project was aimed only at ascertaining the availability of water for irrigation in the district of Licola and in the plain to the left of the Regi Lagni [472] [470] [471]. The data shedlight only on the underground hydrography at the extreme westernedge of the era that interests us. Other one-time studies by the province of Caserta, reported in [471], and recently by the Public Works Office of the province of Campania Province give us an idea of the contour of the aquifer in the middle part and of the upper part of the same Regi Lagni basin (see table IV).

As for the rest of the region, we have the thorough geological investigations cited in the bibliography in a note by Penta on the subsoil of Naples [379], amply illustrated by professors Nicotera and Lucini. Also, Lambertini and her collaborators [271] [272] [273] [274] [275] [276] [277] provided in the same period a notable contribution to our knowledge of underground hydrography as part of their activities at the Institute for Industrial Chemistry of the Engineering Department of [the university of] Naples.

Indeed, as we shall see, these studies provide evidence of the clear changes in the composition of the water as we shift from one area to another within the city and environs. That was noted by earlier researchers [84] [397] and confirmed by Meo [319] and F. Ippolito [254] [255]. All of this lets us reliably assess how the morphology and geology of the region influence how water circulates in the subsoil of the city and surrounding area.

Yet, in spite of the growing number wells and core samples drilled within the urban center and the area immediately around it, if we exclude the area at the western limit of the region, as we have said, few further data were collected, or at least furnished, during that period, regarding water levels in the aquifer. Indeed, among published data, other than the data furnished by Lambertini and her collaborators, only the results by Zei [477] and F. Ippolito [254] [258] have been useful. Among unpublished reports, we have had helpful data collected and kindly transmitted to us by the
Aqueduct Authority about their drilling of wells to look for water in the area north of the industrial zone (fig. 85 and 86). Also among unpublished reports, technicians of the Cassa per il Mezzogiorno have given us helpful information from their work on the sewage lines in the western part of the urban center (fig. 87 and 88).

All other information relative to drilling done for reasons other than those that concern us here, at the most having to do with the elevations of well entrances or ground surface, without more precise values as to absolute values or well location, have given us only some summary indications of shifting in the aquifer since the time of the last measurement by D’Amelio in the urban center and Fiorelli’s measurement in the industrial zone [table V and fig. 64 and 70).

3) Drainage Basins that Feed the Aquifer
        3-1) Recapitulating the conclusions of Lambertini and her collaborators(in table I, II & III following) we report the             complete list of water samples examined zone by zone by Lambertini, and for every zone we provide her values:

        of dry residue at 110º;
        of permanent and temporary hardness;
        of the ratio ───────────, between the millivalences of calcium and
        Mg++ magnesium;
        Ca++ + Mg++
        of the ratio ───────────, between the millivalences of alkaline earths
        Na+ + K+ and the alkalines;
        of the ratio ───────────, between the millivalences of sodium and
        K+ potassium;

As Lambertini observed, the chemical composition of the waters tells us where the SAMPLES come from.

The presence of alkaline earths carbonate and alkalines and thenotable content of colloidal silica in the waters in the industrial area and the north of the city may be explained, respectively, by the aggressive action of carbon dioxide dissolved in the water on calcareous and volcanic rock found in the subsoil and the successive division of the polisilicate acids freed as a result of the assault by volcanic rock. The waters, thus, must come from within the ring of calcareous mounts near Caserta and Nola and from the aquifer fed by those mountains as well as by rain falling directly onto the plain —that is, the aquifer in the type B terrain that makes up the subsoil of the Terra di Lavoro.
Chemical analyses done by the General Consotium for the Reclamation of the Lower Volturno lead us to similar conclusions. They studied water extracted from the wells they drilled to the left of the terminal trunk of the Regi Lagni at the extreme western end of the region. Waters from the urban center and Flegrean zone, however, are totally different.

The waters there are always very sweet and light unless we are talking about the Chiatamone wells and those at the Royal Palace, which contain mineral waters (acque ferrate) that come from much deeper levels than the waters from even nearby wells. At a certain depth in the Flegrean zone, we find mineral waters, or strongly mineralized waters, with a composition and a change variance much different even in very small wells. In these areas, however, we may still find sweet waters with a chemical composition analogous to those in the urban center if the wells are sunk to just a modest depth into the type B materials that we find here and there above the tuff mass.

Mineral or mineralized waters are normal in the Flegrean zone and episodic in the urban center; it is evident that their presence is connected to the last Flegrean volcanic activities. Vice versa, thepresence of sweet or light waters —which we find even at considerabledepth in the urban center and on limited surfaces and at modest depth in the Flegrean zone— can be explained by the infiltration of atmospheric waters and subsequent filtration through the tuffaceous

All in all, in the discussion of the morphology and geology of the region and what we know about the levels of the aquifer (see tables IV and V) we can conclude that, just as Cangiano hypothesized over 100 years ago, the underground waters to the north of the city are fed by the ring of calcareous mountain near Caserta and Nola and by the plain that lies between them and the folds of the Campi Flegrei and Vesuvius.
Different from what Cangiano thought, however, the tormented tectonic activity connected to successive Flegrean and Vesuvian volcanic activity profoundly altered the circulation of waters coming in from THE countryside, shifting their course to the east towards the strip of type B terrain enclosed between the Flegrean complex and that of Somma-Vesuvius, and also to the west into the strip —still type B— bounded by the last layers of Camaldoli and the Regi Lagni. As a consequence, the waters found in the urban center, except for thefew wells that contain mineral or mineralized waters, are fed by the much smaller basin that is enclosed by the hills to the north and westof the city.
Finally, even smaller basins feed the superficial aquifers that produce the sparse waters—not mineral—in the Flegrean area..

3-2) Tables IV and V and some of the figures that accompany the text provide indications of aquifer levels. For some zones, the indications are thorough, and for others they are not. To complete what we said in the preceding section, we would like to stop and emphasize a few things.

As we see from figures 81, 84 and 86, aquifer levels at every point change from one year to the next, and in a given year from one month to the next. In coastal areas, tidal forces can even cause the levels to change in the span of a single day. (Figure 8 shows the differences at various times of the day measured on different days.) Thus, in order to provide a complete picture of aquifer levels at a single point, we need to indicate a median value and fluctuations
around that value. Just as the S.I.I. [trans. note: Servizio Idrico Integrato/ Integrated Water Service] did with the inland wells they studied, we have to record systematically at every point the levelsreached in the aquifer over a long period of time within a year; only then can we show the sequence over time in diagram form such as in figures 81, 84, and 86. Indeed, we might then separate the periodic point-by-point fluctuations from possible variations in the mean seasonal levels. We might thus be able to determine whether, forwhatever reason, the aquifer level has progressively grown or shrunk.

For the same reason, to know the contour of the surface level in the aquifer in a given area and to judge whether or not that contour has changed over time, we need continuous systematic measurements of asubstantial number of points over time in that area, or, at least at the points our data refer to, repeated measurements from the same
season to compare them to those seasons in other years.

Unfortunately, to repeat what we said in the preceding section, continuous and systematic measurements of water levels in the aquifer have been carried out only at some points or in isolated areas:
    -by the S.I.I. between 1929 and 1962, in some inland wells north of the city;
    -by the Aqueduct Authority between 1946 and 1966 at wells in Lufrano, which the same Aqueduct had drilled to          the north of the eastern zone of the city;
    -by the Cassa per il Mezzogiorno, in 1959, in the cavities dug to complete the coastal sewer lines.

Systematic surveys to trace the contour of the aquifer in different periods were done, in turn, by:
    -Fiorelli, in the eastern zone in 1926;
    -the General Consortium for the Reclamation of the Lower Volturno, in the areas of Licola and Varcaturo and to the      left of the Regi Lagni in 1955 and 1961, respectively;
    -by the Office of Public Works for the Campania Region in the centraland upper basin of the Regi Lagni in 1967.

As for the rest, the date we have refer to isolated and one-time measurements done during the drill of wells and core samples and done independently of one another and at different times. Furthermore, as we noted in the preceding section, the values in single wells or core samples are given in relation to ground level withoutspecifying the absolute value [in relation sea-level].

As result, aside from the only approximate values in such data, it is not always easy to deduce whether the differences indicated are the result of the data having been gathered at different periods or because
they are, in effect, real differences in the mean level in the aquifer from point to point. In the same fashion, when the data refer to points in zones that were measured earlier, it is not easy to judge if the differences between the indicated levels and those from earlier periods are due to periodic fluctuations in the aquifer or real variations in the
mean level in the aquifer. In part, we can get around that inconvenience, as we have done, bylooking at the entire complex of data.

In particular, for some areas for which we have no or too few data the contour of the aquifer can be reliably reconstructed (as we did in table IV) by not considering the levels measured at single points but, instead, the field of values that encompasses those points. In turn, the variations of levels in the aquifer over the last few decades, limited to the urban center and industrial zone, may be reliably deduced (as we did in table V) by using as references
D’Amelio’s systematic measurements from 1900-1901, and Fiorelli’s from 1926 and comparing them to measurements taken later, but only if the later ones show levels that are markedly greater or smaller ornearly the same as the earlier ones.

Indeed, we have seen that those points measured in the last few decades that show decidedly greater levels than in the past are almost all localized along the coast. This has led some technicians who have studied the aquifer contour in the city and eastern industrial area to conclude —in their view, legitimately— that the aquifer levels in those areas near the coast have risen notably in the last few decades.

On the other hand, such a rise cannot be attributed to an increase in the flow in the aquifer towards the sea, since, if that were the case, we would also have greater rises at a certain distance from the sea, whichhas not happened according to other data at our disposal. It thus seems logical to look for the cause only in “load losses,” that is, in the
construction of piers and the reclaiming of land near where the aquifer meets the sea. In recent years, such construction has covered the entire seaside areas from S. Giovanni a Teduccio to Posillipo.

Still looking at table V we see that those points measured in the last few decades that show decidedly smaller levels than in the past are, for the most part, almost all localized at a certain distance from the coast, in the urban center and the industrialized areas along a line that follows the path of the Diretissima tunnel in the stretch between piazza
Cavour and pizza Garibaldi. Circumstances and reports bear witness, in accordance with by our data, that in those areas in the last few decades, the aquifer has undergone a notable lowering.

In the industrial zone, there were many wells in operation even in ancient times. The water was used both for irrigation and drinking and was extracted by noria [trans. note: water-wheel]. Most of those wells today have been replaced by deep, drilled wells. Where that is not the case, in order to keep using the ancient wells it has been necessary todeepen the old shaft and replace the noria with submerged pumps. The Diretissima tunnel leaves tuff and continues into type B materials between Piazza Cavour and Piazza Garibaldi in the urban center at a lower level than the preexisting surface of the aquifer. This confirms that both during and after construction of the tunnel, the
aquifer underwent a notable lowering on either side of the path of thetunnel. We have this information from reports of technicians who wereworking on the problems of cave-ins and slides in the overlying steets and buildings at the time.
The reports confirm that the cave-ins and slides were caused by the lowering of the aquifer.

3-3) This is not the place to discuss the useful depth of the aquifer in different zones or, more precisely, the maximum yield that can be extracted from the aquifer before it is exhausted. We should, however, add to what we said in an earlier section (3-1) by noting that in the urban center, where the underground aquifer is fed by a small imbriferous basin [trans. note: imbriferous=fed by rainwater], the aquifer levels undergo notable fluctuations. It filled when the Serino Aqueduct went into service; waters increased in the illegal (“black”) wells then in use. The levels dropped again after the aqueduct was complete and the new sewer lines were activated.

The opening of the aqueduct increased the yield in the subsoil, and that was enough to disturb the equilibrium; the new sewer system was enough to return the levels in the aquifer to their initial state. In the eastern areas, however, where the aquifer is fed by a larger imbriferous basin, continuous extraction on the order of 1 ÷ 2 mc/sec, which was the extracted yield in the last 20 years of the urban aqueduct, the aquifer level dropped by a maximum of two meters. Comparing fig. 86 to fig. 81 and 84, however, we see that those were isolated phenomena in areas where extraction was the most concentrated. This is seen from the fact that if we move just slightly inland, aquifer levels underwent practically no variation.

We move, finally, to local freshwater aquifers found here and there in the Flegrean area. They testify to the modest surface of the basin that feeds them, as seen from that fact that continuous extraction even of small amounts by drilling to below sea-level will enrich the extracted waters with chlorides. The levels in the wells, however, do not vary a lot since they are near the sea; continuous extraction, however, of even small amounts will alter the water balance in the aquifer and cause sea water to move farther inland

END of  PART 2, CHAPTER 5                                CHAPTER 6 IN PROGRESS BELOW
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  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

The Subsoil of Naples
 Part 2 Chapter 6 
(finished  23 Oct 2019)

A Geotechnical Description of the Urban Territory
prepared by engineering prof. Arrigo Croce

Geotechnical Problems in the Development of the City

The geological history of the area around Naples, the morphology of the territory, the nature of the terrains, the cavities in the subsoil, and the underground waters have been illustrated in the preceding chapters of this report. Generally, some of these factors are useful for understanding the various factors at work; others are less important in dealing with what influences the subsoil and the construction taking place within the subsoil and on the surface. Much about the morphology, terrain, and cavities was known in times past (of course, always within the limits of knowledge of a given age), but there are others that we need to consider today.
Technical problems connected to the subsoil have become complex to a level never known before, whether from industrial and commercial expansion within the city, or from the growing needs of the population. The problems can be solved only by looking at their physical-mechanical components and by treating them quantitatively. We can do that thanks to the mathematical methods and experimental procedures now at our disposal through geotechnics. Geotechnical problems really occur at two different moments during construction in the city and thus the problems differ slightly.
Geotechnical problems occur every day. Every time weproject and construct foundations for new buildings, or lay new roads by excavating and moving materials, or carry out underground works destined for a variety of uses. These are localized geotechnical problems, single points that require precise answers. They presuppose a minute, detailed knowledge of the area of subsoil where the construction is taking place or will take place, be it knowledge of the physical-mechanical properties of the terrain, or of the underground aquifer, or of the cavities in the subsoil. Further, the problem doesn’t depend just on factors relative to the subsoil, but on the type, size and dimension of the construction.
They are problems, thus, that arise from the construction of a single manufactured work; they must be dealt when the project is undertaken and investigated on a case by case basis. There are also other geotechnical problems that are less evident when we leave these single cases but very important in the development of the city as a whole and consider the entire urban fabric. That is, we start thinking about the collective stability in an area for a given type of urban or industrial settlement, about the ability of the subsoil to withstand external loads, about the technical solutions and the costs of various hypothetical underground infrastructures, and so forth.
Geotechnical problems of that nature don’t arise from a single piece of construction; they already exist and present themselves at the moment that plans and programs are drawn up for the development or urban renewal of the city. Such plans don’t just consider the usual physical environment, particularly the geological one, but have to make sure that the subsoil is thoroughly analyzed technically and that the are compatible with urban planning. This has to be verified geotechnically. Urban solutions accurately worked out from this point of view can substantially reduce difficulties, even serious ones such as our city has experienced years after episodes of single construction, both public and private. *(1)
*(1) For more particulars, see Croce, A. Il sottosuolo della città di Napoli nei riguardidei problemi geotecnici (1967).

Geotechnical features of the subsoil

Every time a plan is made to build a structure or, generally, intervene on the surface or in the subsoil in any way, the
geotechnical characteristics of the terrain involving the construction have to be investigated. The area might be small, but the investigation has to be detailed. If, however, we are talking about problems of a general urban nature, geotechnical knowledge of the subsoil is concerned with a much larger area, and we have to single out the features that influence that larger urban problem.

(image 89, right , current state of an area between via Petrarca and via Posillipo)

We see, then, how useful it is to know how the geotechnical features of the urban subsoil fit together collectively, allowing us to skip some of the detail and to present the basic data in a more synthetic form. This type of synthetic overview is not just indispensable for large-scale urban planning but also helpa in preventing geotechnical problems before they arise in smaller, single-item construction. For these reasons, this section displays (below) a Geotechnical Map of the Urban Territory on a scale of 1:25,000 (see table VI) drawn on the basis of our current data, which is sparse for some areas. It is easy to understand why such a map, in order to be useful, has to be updated periodically, not just to add more recent data
but, principally, to adapt that data to newer urban planning.
Any graphic display of the geotechnical features of the subsoil
necessarily has to represent a three-dimensional space and, precisely, that stratum of territory that is technically significant. That space is not just the one destined to hold the foundations of a manufactured structure and its underground components, but the larger space around it that is influenced, geotechnically, by that same building. The thickness of the technically significant stratum may, thus, differ from zone to zone in the city. For the moment and as a first approximation, we may assume that thickness to be about 50 meters. Naturally, the first and most evident element that characterizes the space in question is the surface area that confines [a potential structure] and the morphology, as amply illustrated in chapter II; thus, table VI shows contour levels.

Another fundamentally important element, analyzed in chapter V, is underground water, which, because of the hydraulic features in our city, can be simply but effectively represented by the free surface of the aquifer.*(2)

*{2. The contours of the aquifer shown in table VI, relative to the central and eastern parts of the city, are deduced from table V, Falde nel centro cittadino [Aquifer in the urban center]. For the area of Coroglio, the contour curves have been traced using data gathered from recent drilling.}

The other elements shown on the geotechnical map have to do with the location and physical-mechanical properties of terrains present in the subsoil, and it is at those points that we pause briefly.*(3)

*{3. Regarding the physical-mechanical properties of volcanic terrains near Naples, A. Pellegrino’s journal is useful: Proprietà fisicomecchaniche dei terreni vulcanici del Napoletano [Physical and Mechanical Properties of Volcanic Terrains in Naples (1967).]}

In the meantime, we should remember (see chapter I) that the underlying structure of most of the urban territory is made up of lapideous rock formed by auto-cementation of ash, pumice and otherdetritus thrown up by the Flegrean volcanoes and known as yellow Neapolitan tuff. Yellow tuff is almost always covered by a more or lessthick blanket of loose terrains also mostly of volcanic origin.

Yellow Neapolitan tuff

Various kinds of volcanic tuff are present in the area of Naples; by far, the most prevalent kind is the so-called chaotic yellow tuff or yellow Neapolitan tuff. It, in turn, varies as to the percentage, sizes and porosity of the various inclusions dispersed in the cineritic mass. Within the tuffaceous formation, there are no true levels of stratification in the sense of regular discontinuous surfaces of the kindso evident in typical sedimentary rock. There are, rather, numerous fractures that run through the mass in different directions, fromsubvertical to almost horizontal. These fractures are often quite extended, and where they meet they form large, irregular prismoids.

It follows from this that the behavior of such formations under stress from external loads depends on the geometry and mechanical properties of materials along those fracture lines in those spots where they are frequent. Particularly important is how the fractures are distributed and oriented in relation to the external load. If no suchfractures can be verified, then the breaking point of the lithoid massbecomes extremely important. We know that the breaking point of tuff varies according to water content and degree of lapidification. In general, we can say that [tuff] is a lapideous rock with a mean cohesion on the order of some tens of kg/cm2 at an angle of attrition of around 25°.

In spite of the low resistance to breaking, certainly not comparable to those of compact or hard lapideous rock, and in spite of the surface fractures, yellow tuff can still withstand notable loads and insure the stability of relatively large excavations. It follows that one of the most significant elements on the geotechnical map of our city is the presence or lack thereof of the tuffaceous formation in that part of the subsoil under consideration. In effect, that formation is
present in almost the entire urban territory, either as outcropping or, more often, at variable depths beneath the surface.

The presence of the formation is indicated in table VI and is marked in yellow of varying shades to distinguish the depth of the tuff roof from absolute ground level, this in relation to problems of foundations.*(4) More precisely, three intervals were considered: from 1 to 5 meters; from 5 to 30 m.; and more than 30 m. For the first, there is no doubt
that foundations should reach the tuff; for the second, there is the alternative of transmitting the load directly to the tuff or to the overlying loose materials; finally, beyond 30 meters, the tuff formationis of no technical interest at least for the most frequent kinds of construction since it will almost always be possible to transmit loads toloose terrains on top of the tuff.

*{4. The contour of the tuff roof in relation to the urban center is also shown in tables I and II on a scale of 1:10,000.}

Areas where there are outcroppings of tuff or where it is at depths of less than 5 meters from the surface are found on the slopes and upper reaches of the hills of Posillipo, Camaldoli, San Martino, and Capodimonte. There are also tuff outcroppings farther to north in Chiaiano and Marano.

The tuff formation is present at greater depths, from 5 m. to 30 m., in a large strip about 8 km wide and extending from the coast to the interior from NW to SE, between via Caracciolo and the port. It comprises almost the entire low part of the city, the hills of Camaldoli, Vomero and Capodimonte as well as the zone farther to the north as far as the towns of Marano and Marianella. The tuff in the Posillipo hill is of the same kind.

Finally, the tuff roof is deeper than 30 m. in the area at the NE of the city territory, including the towns of Secondigliano, Arzano, and Melito, and in the SW, including the towns of Fuorigrotta, Agnano, Pianura,and Soccavo. As in many old cities, various cavities have been dug within the tuffaceous formation over the ages, including wells and channels to supply water. Thus, before beginning any new construction project, we have to know whether or not there are any cavities within the formation that might affect the stability of our project. The problem of finding such cavities is not difficult in principle, but, in practice, turns out to be so. Many cavities can be reliably found and measured by direct exploration; among these, of course, are road and railway tunnels. Others have been only partially found or incompletely explored, and some no longer have discernible entrances and haveescaped detection and measurement. Besides that data —documented in attachments to this report— historical investigation such as illustrated in chapter IV has been very helpful.

image 90 (above, left) - Via Nuova Camaldoli; artificial embankment with inconsistent soil: visible is a natural valley cut through the series of volcanic layers from area eruptions.

From these elements we find that it is, indeed, possible to find more or less relevant cavities almost everywhere in the urban territory, but that older cavities are usually concentrated in certain areas of the city. It is those areas, where the cavities appear as relatively characteristic of the subsoil that are dealt with in table VI. Past data about cavities in the subsoil have, no doubt, been useful— just as future data will turn out to be—, but it is up to those who plan and build to find out if a foundation for a new building is going to be too close to such a cavity. In that regard, we must bear in mind
that current geophysical methods are not up to that task, and that wehave to rely on mechanical probes. Older excavations generally turn out to be quite solid, even though we do find some fallen bits of columns and vaults, or some fractured pillars. Here, we note that even these older cavities were dug in what appears to have been tuff of the highest mechanical quality

image 91 (above, right) - an entrances to a tunnel dug for the extraction of lapilli, loose volcanic stones. Such tunnels are abandoned today.
Loose terrains
Almost all loose terrains in the subsoil of the city are of volcanic origin, and they show great variety as to particle structure and size. In situ there are often very small stratifications, variable from one to the next even when close together. If we look at the physical-mechanical properties, we see that from a technically and as a first approximation, the loose terrains in question may be grouped into:
    —pozzolana subtly interspersed with pumice;
    —beach sand;
    —irregular mixtures of volcanic terrain, alluvial terrain, and organic matter.
The pozzolana interspersed with pumice is found in most of the city territory; the sand is present along a narrow strip that runs from the beach at Mergellina to S. Giovanni a Teduccio; and the third group, themixture of volcanic terrain, alluvial terrain, and organic matter, is found in the flat areas at the eastern boundary of the city as well as in
the flat area of Coroglio.
We note in passing that artificial accumulations of terrain, collected over the years, are often found along the flanks of hills or as fill in old trenches and valleys and even along the coast.

Pozzolana and pumice differ as to granulometry; pozzolana is finer and the structure of pumice particles is clearly more foam-like or spongy. These features may vary along the vertical, but statistically appear to be relatively constant throughout the entire territory. Pozzolana and pumice behave simply and similarly under external stress. Indeed, because the aquifer is at a notable depth from ground level, the terrains included in the technically significant strata are less than completely saturated because of their greater permeability, particularly pumice, and applied loads are transmitted immediately to the solid [tuff] framework. As a result, the course of deformation over time is very fast and the resistance to breaking is, in practice, not bound to how stress is applied.
The compressibility of the terrains is, on average, the same, but it does show greater variability in the mean value as we go from in situ pozzolana to disturbed pozzolana and then to pumice. Resistance to breaking depends essentially on porosity and is characterized by relatively high values for angle of attrition and, often, non-null values for cohesion. Ccohesion of pozzolana, however,  depends on several factors that do always act simultaneously and that  are subject to external influences, particularly the action of water, which can act in various ways. It follows that in some circumstances cohesion can be notably reduced and, from a technical point of view, should be disregarded or at least considered with extreme caution.
In pumice, cohesion is effect of reciprocal juncture of particles, which is facilitated by their roughness. The cohesion of pumice is also influenced by external environmental factors, particularly near the outside surface of the front of an excavation or on natural slopes where dynamic factors come into play.
We thus see that where pozzolana is interspersed with pumice, the urban subsoil may be characterized relatively simply, geotechnically. There are two circumstances that are almost always present: (1) the simple and practically uniform behavior of pozzolana and pumice under external stress [loads] and (2) a very similar range of variation in their physical and mechanical properties.

Beach sand displays notably uniform properties

The irregular mixtures of terrain of various sorts, on the other hand, are quite diverse in their geotechnical characteristics; however, they are only a small part of the urban territory. We can say, however, that although the loose terrains in the urban subsoil are diverse and display different physical-mechanical properties, we can still describe them geotechnically, if somewhat generally. As a first approximation, we refer to the grouping, indicated above, which does take into account the essential features of the terrains in the technically significant strata.

  images 92, 93, 94 (left, center, right) Camola Ricci Park: entrances to the large "Mangni"quarries: 92, an overhead viaduct    connecting a large residential area within the city, being built above the cavities. Particulars in 93 & 94.

To evaluate the mechanical properties, we can resort to in situ tests, particularly to those done with a static penetrometer. Analyzing the mean resistance at the point along a number of verticals, we see a notable uniformity even over a large area. We noted five typical kinds of resistance at the point of the probe. They were a function of depth and are shown in table VI.


Geotechnical problems depend on factors relating to the subsoil, which we have mentioned, but the problems also arise from the interaction of construction with the subsoil. Man-made man can be grouped as to
—type, geometric and structural features, state of conservation of the building and relative foundation, including    retaining and supporting structures;
—nature and intensity of the load transmitted to the subsoil;
—underground canalization for aqueducts and sewers.

With single structures, these factors can be determined with no
difficulty. At a more general level, however, there are blank spots, fragments and imprecision in some of our available data. It is, thus, currently not possible to compile a map of the urban fabric that displays meaningful parameters in a geotechnical sense. Some elements may be deduced from various statistics and we shall refer to those in this section. For static conditions of structures or, better, for shifting and cave-ins that affect those structures, we refer to chapter 9 in this report. For material on aqueducts and sewers, see chapter 7 and 8.

It helps to look at the evolution of the city over time. The dates that seem to be the most significant in that regard are the end of the 15th century and the years around 1920. Figure 97 (below) shows the perimeters within which those periods of urbanization seemed consistent and characterized by certain types of construction. The oldest nucleus of construction was formed of buildings that for the most part were made of walls of tuff blocks with foundations of arches and pillars; floors were vaulted or wooden. Later, tuff continued to dominate the construction of walls, but the use of continuous foundations for buildings became common, vaulted floors were no longer used and flat floors supported first by wood and then by iron came into use. With the advent of reinforced concrete, older construction methods rapidly disappeared. Today, foundations are mostly pillar foundations, and the pillars are drilled.*(5)
*{5. For particulars, see Sapio, G. Fondazioni (in press).}
(images above: 95, left. - Camola Ricci "Park"; 96, cavity by the Cacciottoli slope above Corso Vitt. Emanuele.)
A statistical study on subdivisions by administrative unit within theurban territory has been carried and the most significant results are shown in table and figure 97.*(6)

*{6. The study was done on the basis of data from the Statistical Annals of the city of Naples and the Regolatore plan for 1958. Both the census for 1931 and 1961 were taken into account, as were demolitions between 1931 and 1939 in the sections of S. Giuseppe and Fuorigrotta, as well as damages caused by WWII. The count of rooms built before 1931 and still in existence in 1961 disregarded construction between 1931 and the end of WWII and demolition between the end of the war and 1961.}
The following overall data are very interesting:
    —rooms existing in 1931 508,527;
    —rooms demolished from 1931 to 1939 or destroyed in the last war 117,432;
    —rooms existing in 1961 786,210;

We can say to a good approximation that in 1961 the rooms in existence and built before 1931 came to about 390,000 or 50% of the total existing rooms. That is, well over half the rooms currently
[1967] in existence have been built in the last 15 years; thus, most of that was with reinforced concrete, almost always on pillar foundations. Moving from the general to the specific, we note that the picture changes from one section of the city to another. We see that the sections of Montecalvario and Stella were built almost entirely before 1931, but also that most of the construction in S. Ferdinando, S. Giuseppe, Avvocata, S. Lorenzo, and Porto is older [than 1931].

We see in these sections of the city examples of older constructions, worn by time, and modified and transformed in often debatable fashion from the point of view of stability. As far as the intensity of load transmitted to the subsoil goes, the only
element that need concern us is the construction density; that is, the ratio of rooms to total surface area.*(7)

{7. There are no recent statistics on the height of buildings or number of floors per building that might let us better evaluate the load distribution on the terrain. There was a study of that kind in long-ago 1884. It does have some interest today but, of course, is totally obsolete.}

Construction density varies a great deal throughout the urban area. In the oldest areas —Pendino, Porto, S. Giuseppe, S. Lorenzo— the density is very high: from 452 rooms/ha in S. Lorenzo to 250 rooms/ha in S. Giuseppe [trans. note: We are using “room” to translate the Italian “vano,” (plural, vani)  which is actually any space in a home; that is, 1 bedroom, 1 bathroom, and 1 corridor are 3 vani. Also: ha is the abbreviation for hectare; 1 ha is equal to roughly 2.5 acres.] In those areas, fewer rooms were built after WWII then were destroyed during the war, itself.

In those sections where urbanization occurred in the 18th and 19th centuries —S. Ferdinando, Chiaia, Montecalvario, Avvocata, Stella, San Carlo all’Arena, Vicaria and Mercato— construction density remains high. In some of these areas, urbanization has only recently been completed, as in Chiaia, Avvocata, and San Carlo all’Arena. Wartime
damage was high, as was subsequent reconstruction, and thus the percentage of rooms in those areas that were built after the war is relevant: 37% in the Chiaia section and 86% in the Mercato section. Among the remaining sections, urbanized in the 20th century, construction density is markedly lower except for the Vomero section, where a density was reached of 363 rooms/ha, which is equal to the density in the historic center of the city.

Of the almost 400,000 rooms built between the end of the war and 1961, 26,000 of them were built as additions above original top floors or as other extensions of older buildings. We have no data that breaks down that “repartitioning” of older buildings by city section, but there is no doubt that most of it is in the historic center and other central areas of the city: S. Ferdinando, Montecalvario, Avvocata, Stella, Pendino, Porto, and S. Lorenzo. Since there were 42,146 rooms built in those areas from the end of the war until 1961, we can say that about half of them were done through such modifications.

Geotechnical Characterization of the Urban Territory

The factors that we have considered in preceding sections relative to the subsoil and urban fabric have to be looked at together in order to decide how to sort out the geotechnical problems of the city. The data at our disposal, are often sparse and fragmentary and thus insufficient for a complete geotechnical characterization of the city. In spite of that, we didn’t want to give up entirely on presenting some sort of a synthesis that might serve as a first approach and prove useful to further studies.*(8)

*{8. For further details, see Croce, A., Pellegrino, A. Caratterizzazione geotecnica della
città di Napoli (in press).}

As a first approximation, our city can be subdivided into six zones (see table 7) in which geotechnical problems are, essentially, relatively uniform.

Zone 1
This is the largest zone and makes up the high part of the city, that is, the hills of Posillipo, Camaldoli, Vomero, S. Elmo, Capodimonte, and Capodichino. The elevation of the area is generally between 50+meters and 300+ m. with a maximum of 457+m. at Camaldoli. The morphology of the zone is hilly. Except for a few flat areas, the surface is constantly inclined to as much as 30-40%. The inclines are pronounced not only at the edges of the area but in the interior on the slopes of small valleys that furrow the zone.

Openings into the San Gennaro of the Poor catacombs, with
  the St. Mary of the Incoronation church seen above.

The yellow tuff formation is present everywhere. It outcrops (or almost) in various parts of the hills of Posillipo, Camaldoli, Vomero, S. Elmo, Capodimonte and Capodichino. In the NW it is generally struck at a depth of about 15 meters, and farther to the west in that same area at 60 m. and deeper. At the roof of the tuff, we find pozzolana interspersed with tiny bits of undisturbed pumice. The mechanical properties of these terrains at Posillipo, via Cilea, and around Piazza Medaglia d’Oro gradually improve (see penetrometric profile of the 3rd type in table VI) to a depth of about 15 meters and then stay almost constant.

At the limits of the area under examination near Secondigliano and Melito, the mechanical properties of the terrain covering are notably worse; these areas registered the lowest values for resistance in the entire territory although the probes went down to almost 30 meters (See penetrometric profile of the 2rd type.) The aquifer is quite deep in all places and, thus, does not influence normal construction. In the area we are examining there are many large and relatively old cavities that go back to the days when all the excavation was done underground. Some of these old quarries can still be easily seen on theslopes of the hills. As well, in the same areas, we find examples of more recent open-pit excavations. It should be noted that in the past even the loose materials on top of the tuff were used as construction material, particularly pumice. Since it is present in various subtle strata, it was extracted via very small shafts.

As a result of development, there have been some very recent and important modifications in the entire zone. Whether to build roads or to clear space for buildings, the slopes of the hills have been broadlyand deeply cut into and terraced. At the same time, earth has been moved even to the extent of filling in valleys. The need thus increased for more retaining structures, which, however, were mostly built with tuff blocks and only occasional reinforced cement. In that regard, we note that the planning of such retaining structures often relies on the cohesive properties of pozzolana, cohesion that, as we have seen, can often be modified by atmospheric activity. And we also point out that such retaining structures are almost never provided with efficient drainage. As far as moved earth goes, the mechanical properties of the terrain involved are often inferior, either because of the nature of the materials, themselves, or because they were moved into place improperly. Zone 1 includes almost all areas urbanized in the 20th century. Only
Avvocata and Stella were urbanized before that.

cavities as car parks & storage
Most of the buildings are dwellings for the general population. In the oldest parts, Avvocata, Montecalvario, and Stella, the density ranges from 375-166 rooms/ha. In the newer areas the density is markedly lower and often less than 50 rooms/ha. The exception is, as we noted earlier, the Vomero section. Except for the oldest sections, construction in this zone is very recent or recent: 50% of the buildings are from the last 15-20 years and rest from a few decades earlier. This zone poses interesting questions regarding the urban fabric of the future. Since this is the zone with lowest construction density, it is easy to image that it is here that new development will be particularly intense. In that regard, we should bear in mind that quite a few of the free areas are on slopes of hills, some of them with marked inclines, and other areas are on ground that is very uneven. Urbanization in this zone will inevitably bring with it large-scale excavation and earth moving that could worsen the situation on the slopes and actually endanger stability, particularly where the tuff formation is deep.

Before considering urbanization, we need a detailed study of the stability of the slopes. In any event, urbanization should only occur within an overall plan that considers everything that has to be built,
including aqueducts and sewers and that plans how construction is going to be managed and in what order work shall proceed. In the sections of Secondigliano and S. Pietro a Patierno the tuff formation is at a notable depth. Loads on the surface will thus rest on loose terrains that are on top of the lapideous formation. As we have said, from the few data at our disposal, the mechanical properties of the terrains in these areas are on average inferior to the same types of terrains found in other parts of the city. We thus have to do some real research and proceed with caution before undertaking any further construction in these areas.
Zone 2
This is in the SW of the city territory and is bounded by Monte S. Angelo, the Astroni, and the Coroglio plain. The surface is nearly flat or slightly inclined, with elevations between 20+ and 50+ meters. The subsoil is loose terrains down to a considerable depth; for example, the roof of the tuffaceous formation struck at a depth of 103 m. at Piazza Leopardi and at over 110 m. at via Marconi. The loose soils in situ are generally pozzolana and pumice, but on the surfaceand even down to a certain depth they are disturbed.

The mechanical properties are notably uniform throughout the entire zone. The penetrometric profiles are of the first type with resistance at point that increases noticeably with depth, always reaching relevant values and occasionally very high values. The aquifer is at a minimum depth of about ten meters. Throughout
the zone, the subsoil has not been modified by manmade structures either below or on the surface. It is only recently in the extreme northof the zone that earth has been moved in order to fill in some valleys;
this has been done in the same careless fashion that we have already mentioned in reference to zone 1.

Most of the Fuorigrotta and Bagnoli sections of the city fall within this zone. Construction density is low, about 28 rooms/ha in Fuorigrotta. Almost all of the construction is given over to housing for the general
population and has been built since the end of the last war. Because of the current low construction density, it is easy to predict that the zone will be notably affected by urban development. Considering the nature and characteristics of the terrain, there should not be any particularly important technical problems.

Zone 3
Zone 3 forms a triangle bounded by the Posillipo hill, zone 2, and the sea. The surface is almost level, with elevations up to about 10 meters. In this zone, too, loose terrains are found at great depths and are volcanic —pozzolana, pumice and lapilli— mixed with a variable percentage, often quite high, of vegetable fragments and organic material. These are terrains transported in either by old rivers thatused to traverse the zone or by the sea. The upper surface of the aquifer is at a depth of only a few meters. There are not a lot of data on the mechanical properties of these terrains, but we feel that they have a reduced ability to resist external loads and a high compressibility.The zone has already been entirely covered by industrial construction, among which are noteworthy enterprises such as the Italsider steel mill and the Cementir cement factory.

Zone 4
Zone 4 is at the center of the city territory and consists of the ancient Greco-Roman city. The surface is nearly flat or slightly inclined with elevations between 10+ and 50+ meters. The Pizzofalcone promontory
is an exception and is quite high, dividing the zone into two parts. Yellow tuff is present everywhere and outcrops at some points but is normally struck at a depth of 10-20 meters. The thickness of the formation is always considerable. Pozzolana is found on top of the tuff roof and is thinly interspersed with pumice, mostly undisturbed. For these terrains we have no results of penetrometric probes.

The aquifer is at variable depths, ranging from a few meters to a few tens of meters, which could cause problems depending on place and circumstances. Human activity has caused great modification in this zone both below and on the surface. In the eastern part —the area of earliest urbanization— there have been many cavities dug in the tuffaceous formation over the years at different depths and for different purposes: tunnels and wells for the Bolla and Carmignano aqueducts, storage spaces of one kind or another, catacombs, small tunnels dug just to extract building stone for a single building, and so forth. We point out that it not rare to find cases of overlapping cavities —that is, one built on top of another at different depths.
Most of these cavities were abandoned long ago. Many have been filled with materials thrown in by man or by fragments fallen from their own walls. Other cavities, quite a bit smaller, are found in the loose terrains above the tuff formation, particularly in the banks of pumice. Those cavitieswere dug in order to extract that very material to use in the construction of vaulted attics. On the surface we find earth that was moved in long ago to fill old river beds so they could be built upon or to adjust uneven areas in some spots.

Zone 4 is entirely and intensely urbanized. The buildings are for housing of the general population, offices, and some smaller spaces for workshops and the like. There are many important monuments in this
zone. The part to the east of the Pizzofalcone promontory is the historic center and that part of the city already in existence in the 1700s. That nucleus has remained largely unaltered. Some limited exceptions are found on either side of via Rettifilo [Corso Umberto], on via Duomo and via Mezzocannone, areas rebuilt at the end of the 1800s [ed.note: in the urban renewal of Naples known as the risanamento), and also in the area of the new Carità quarter, rebuilt in the last few decades.

Reinforcement a quarried wall
in a cavity at Capodimonte
Construction density is very high. It is always above 300 rooms/ha and reaches 452 rooms/ha in the section of S. Lorenzo. The buildings are generally old. Statistics show that 70-90% of the spaces were built before WWII, but that is better understood by noting that much of the construction is from earlier centuries. Construction has picked up in the last few decades; about 10-30% of the spaces have been built since the end of the war and, depending on the area, as much as half of that has been built as extra floors above original roofs or by otherwise modifying pre-existing buildings. The western part of zone 4 is the Chiaia section. The construction there is somewhat less dense and much more recent.

For some time now, there have been
urban renewal proposals to evaluate the situation of our many monuments, of replacing old and anachronistic buildings, and, generally, of facilitating transportation both below ground and on the surface. New buildings can be taller than existing ones and have foundations directly on the tuff formation or on the overlying loose terrains. The choice will depend on the kind of load as well as on the history of how the subsoil has been disturbed previously—that is, the presence of moved earth, older buildings and cavities.

A section of the Bourbon Tunnel
at via D. Morelli

Those are the points that should be the focus of attention in investigating these foundation terrains. Future underground construction will effect the tuffaceous formation and, to a lesser extent, the overlying loose terrains. The presence of the aquifer can assume great importance on projects for such construction, whether because of technological problems or whether changes in the aquifer might influence stability of buildings directly above on the surface or in the areas around excavations. We do well to remember the mishaps that occurred during construction of the Metropolitana on the stretch between via Foria and Corso

We should also bear in mind the condition of most buildings built of tuff blocks: they have older foundations, and many are multi-storied with one or more floors a result of additions to the top of the original structure. We are dealing with buildings that could be seriously affected by even small movements in the subsoil caused by nearby excavations.
Zone 5
This is a narrow strip along the sea in the Gulf of Naples from Mergellina to S. Giovanni a Teduccio. The surface is flat and elevation is about one meter. The entire zone consists of land-fill with various materials, most of which were put in place at the end of the 1800s. The fill is usually a few meters thick. Beneath the fill there is a typical formation of beach sand consisting mostly of lapideous lapilli.

Underground station, state railway system,
Piazza Garibaldi

 Along the entire stretch from Mergellina to the Granili, the tuff mass is struck at about 20-30 meters with a thickness that gradually decreases. Near the Doganella electrical station, the formation seems to be almost absent, but it reappears a little farther to the SE. According to Guadagno, this is the point at which the Flegrean tuff terminates and another kind of tuff begins, a product of Somma-Vesuvius. For technical goals, however, there are no significant differences in behavior between the two, at least according to our experience. The aquifer is present a short distance below the surface. The mechanical resistance of the loose terrains that cover the tuff roof increases down through the first few meters and then stays constant to about 25 m. (penetrometric profile type V).

Very precise leveling seems to indicate that the zone is subsiding. All of zone 5 is covered by various kinds of construction along this arc of the gulf: general dwellings on the western stretch from Mergellina to Santa Lucia; port facilities and older dwellings in the east; industrial plants of a certain importance, among which are the three ENEL electrical power generating plants in the stretch from the Granili to S. Giovanni a Teduccio. Construction density is very high. As far as dwellings for the general population are concerned, the process of replacing olderbuildings has begun in the entire zone, and this will continue in the future, particularly in the east.

New buildings can be taller than current ones and their relative loads can be transmitted to the tuff formation of overlying loose terrains where perimeter walls extend down to shallower shared foundations or deep foundations, as is currently the practice.The presence of the aquifer at shallow depth and the absence of cohesion in the loose terrains on top of the tuff roof become very important technical decision on how to excavate due to such things as the lowering of the aquifer. For the same reasons, the best kind of foundation should employ the normal type of drilled pillar.
Zone 6
This zone extends to the eastern limits of the city of Naples, at Somma-Vesuvius. Ground level is nearly horizontal with elevations of a few meters. Until a short time ago, the area was occupied by “marshes” furrowed by water courses that collected water from the surrounding hills. Among these waterways, the largest was the Sebeto [river]. With the passing of time, there waterways were channeled off both on the
surface and underground such that the Sebeto river has now practically disappeared.

Escalator from surface ticket
to underground rail station

The subsoil in this zone is much different than the preceding ones. Tuff (see table VI) is only marginally present and is a bank of modest thickness, from a few meters to about 20 meters. As for the rest, the subsoil is made up of disturbed loose terrains, for the most part Flegrean and Vesuvian pyroclastic product —pozzolana, pumice, lapilli— mixed to varying degrees, often considerable, with vegetable fragments and organic material, frequent peat-like banks of some thickness, very fine grains of clay and coarser gravel carried here by the waters of the inland hills of the Apennines. Frequently, the phreatic stratum is almost at the surface. In this zone, there is a notable extraction of water from varying depths both for consumption and for industrial uses. The various characteristics of the subsoil are completely mirrored by the penetrometric profiles. Mean resistance along any vertical changes considerably and alternates depending on depth from very low values to relatively high ones (penetrometric profiles type 4).

ticket window, state railway system,
Piazza Garibaldi

The sections of Vicaria, Poggioreale and Ponticelli are in zone 6; the construction there is mostly housing for the general population. The Industrial Zone and Barra are also in zone 6, and there the construction is almost exclusively industrial. This last type of construction consists largely of one- or two-story sheds for relatively small and lighter-weight machinery. Even the dwellings are relatively small. In spite of that, there have been some mishaps due to improper foundations. Some of the troubles have also been due to wells that, besides causing the upper surface of the aquifer to sink, have caused erosion even at some distance away. That has affected the subsoil. The loads transmitted to the subsoil in this zone are not heavy.

This explains why, in spite of the inferior characteristics of the foundation terrains, there have not been particular problems in planning and putting up buildings. Larger structures, however, would require changes to our current thinking on how to build in this zone from both a technical and a financial point of view.

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