Naples:life,death &
                Miracle contact: Jeff Matthews


Underground Naples Portal

These are the entries in
Naples: Life, Death & Miracles dealing the caves, quarries, tunnels, aqueducts, catacombs, subway construction sites and archaeological sites beneath Naples and a few elsewhere.

Amalfi - Beauty & the Beast
Ancient port of Neapolis
art gallery, on-line
aqueducts (1)   (2)
Beneath Mt. Echia
Beneath the Oldest Basilica in Naples
Big Archie & Living on the Edge
Big Money Pit, the
Bourbon Tunnel, the
bunker photos at NUg
Bussento caves, the
Camerota Caves
Campo Soriano Natural Monument Park
Cami Flegrei (alias Flegrean Fields)
Castelcivita Cave
catacombs (1)    (2)
catacombs, Jewish
Cavallone grotto (Abruzzo)
Cave-ins and sink-holes
Cavern of Mithra, the
Caves & Tunnels & Holes in the Ground
Caves for a song
Cavone, the
Cistern (Roman, in Caiazzo)
Coastal Caves (1)  (2)  (3)
Cocceius, Lucius Auctus
De Marinis, Fulvio
Drive-through cave, a (Sardinia)
Fontanella Cemetery, the

Gauro Mt.
Greek tombs
Grotta di Cavallo & early humans
Grotta di Maria Cristina

gullies of Puglia (Belvedere 'lama')

Ħal-Saflieni Hypogeum (Malta)
Ischia & "Countries of the Mind"
Ischia, the Grottoes of
Karst Caving
Magnificent Magmathon!
Matese massif
Meri karst pits of Mt. Soratte (Rome)
Metro construction (running series)
Miseno
Neapolitan Crypt, the
New Trains & Old
Olympics
Nicolardi (via), cave-in (2015)




What's this? No, it's not construction for
  a new metropolitana station. Click image.





                         
Oldest Bridge in Naples, the
Oracles of the Dead
Paglicci grotto (Gargano)
Pertosa Caves

Pianura sink-hole (2015)
Proud to be a Troglodyte
Pseudo-Sibyl of Averno
Roman amphitheater in Naples
Roman Port, the
Roman tunnel at Cuma
San Lorenzo archaeological site
S.M. di Pietraspaccata (cave church)
Seiano Grotto, the
Sewerage system, the
Sicilian channel monolith
Stiffe Grottoes
Stone-cutting
Stone-cutting (signs & symbols
Strange Fate of the Naples Netherworld
Subsoil of Naples, the
Templar crosses beneath Naples?
thermal baths discovered
two grottoes near Frosinone


   I call your attention to the entry (just above) "Subsoil of Naples." It was
published in Italian in 1967 and appeared on-line in English translation in 2003. That on-line version has since disappeared. I am trying to put it on this site. If you want to know why everything on top of the ground in Naples is so chaotically overbuilt, you have to know what is under the ground. My version is a new translation (I also did the original).
It is now finished.
The last chapter in The Subsoil of Naples is directly below. jm

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    From the hindsight of 2019: This last chapter of Part Two is the least technical of the nine chapters. Readers don't have to be geologists or urbanologists or put up with statistics and equations. It's a straightforward explanation of what can happen to streets and buildings of a city if the right persons don't pay attention to what is going on beneath the city. Essentially, there are a few things that can go wrong, and if they all go wrong at the same time, you've got problems.


This is Part Two, Chapter 9, the last chapter in part two of

The Subsoil of Naples

Chapter 9
Causes of Movement
by the member experts of the entire Commission
named on 29 September 1967


Movement of varying degrees in and on the subsoil  —from simple cracks in buildings to full-scale collapses of buildings and retaining structures and the opening of sink-holes in the streets— are unfortunately not a new phenomenon for the city of Naples. They have increased over time and affected most areas of the city, becoming a plague that afflicts the city and a cause for justified concern and alarm on the part of the public. We have to interpret the causes correctly. We have to examine the evolution of soil movement over the years and see if and how it is different from one zone of the city to another.
We also have to determine if and how the environmental situations that might cause such phenomena have changed with time as we move from area of the city to another. The Italian term for such movement is dissesti (plural). By that, we mean phenomena in the subsoil that affects structures of all kinds, from buildings to streets, sidewalks, underground maintenance structures, retaining walls and man-made structures of all kinds.
[translator's note: I am using "movement" or "movements" for dissesti. The Italian word , however, means an abnormal and sudden shifting, quite different from the term movimento or movementi (plural), the general terms for all movement.]

image, above: Retaining wall collapse and street cave-in on via Tasso (June 1966)
Historically, there has been no lack of studies of soil movement and attempts to deal with the problem. The building edict issued by Ferdinand IV of Bourbon on 3 October 1781 was the first such provision of a general nature to try to put a stop to the chaotic building practices of the day, much of which actually went back to the ill-considered practices of the Spanish viceroys in the 16th and 17th centuries. The edict had 10 articles; number 4 is particularly interesting. It said that the cause of so many cases of collapse in buildings was the practice of digging "underground caves and grottoes" to extract stone for building material; the edict forbade henceforth any such digging on the premises of buildings or outside on the public streets.
The edict also restated the prohibition of 30 May 1588 and 9 October 1615 against any further excavations on the slopes of the Vomero hill near Montesanto and above the Spanish Quarters all the way up to the San Martino monastery. Other important articles in the Bourbon edict dealt with the maintenance of buildings in dangerous condition, the disrupting long-term presence of scaffolding used to prop up such buildings (even back then, they were everywhere in the city); the need for quick repair and restoration, the need to check the professional competence of engineers and others working in that field, and the need for quality control of materials used in construction, particularly the materials used in the foundations of buildings. The edict of 1781, then, was a clear testimony to the disordered state of the construction industry as well as an expression of concern over the stability of buildings in the city.
That edict was followed by other provisions issued by the Building Council of Naples in the first half of the 1800s in an attempt to get some control of the excavation of tuff and lapillo (smaller, round fragments of hardened lava) as well as to map both the surface and underground areas of the city. More recently, other commissions have studied the subsoil (see bibliography) and have come to a number of conclusions that we summarize below:


images:
above left, Wall instability and resulting collapse of roadway at via Catullo (March 1966)
below right,
Street cave-in at Corso Meridional (Oct. 1956)

    1) 1892. A commission was formed in the Ministry of the Interior to deal with the safety of streets and buildings. Their task was to explore thoroughly and survey the underground and all of the old cavities dug to get tuff and lapillo, and, indeed, all other cavities; further, to repair the public and private sewers (especially in the sections of S. Ferdinando, Montecalvario, Avvocata, S. Giuseppe, S. Leonardo, and Vicaria) such as to prevent infiltration [of waste] into the subsoil; further, to prohibit private parties from dumping materials into cavities, wells or cisterns, and impose checks and repairs of wells and other spaces beneath buildings; further, to oversee  the internal canalization of the waters of the Serino (river); and to have the Municipal Technical Office inspect buildings in hazardous condition and file the results for future reference.
    2) 1934.  A commission was  appointed by the Engineers Union of the Province of Naples after a series of collapses in 1933-34: Their task: survey structures in the subsoil as well as the basins and channels of the Bolla and Carmignano aqueducts; regulate public services that have to do with the subsoil, particularly regard the sewerage network; regulate the secondary services; regulate tramways to ensure proper grounding of electrical current and reduce vibrations in the subsoil and excessive traffic noise; insure isolation of electrical conductors in the subsoil; document with building permits the assays conducted; this will help establish stability and detail how given conditions relate to the construction of new buildings, especially the foundations; make a general inventory of retaining walls, of filled areas and dwellings and require owners to show a certificate of stability from an engineer; establish provisions for high tuff walls that border on public and private roads; adjust rain run-off collectors and effectively maintain the sides and slopes of covered river-beds; institute in the Fire Department a construction section under the auspices of engineers from the City Technical Office to deal with disasters.
3) 1956. A municipal commission was formed to pinpoint the causes of the frequent episodes of static movement of buildings. Because of the limited time at their disposal (results were delivered after less than one month of work) the commission's conclusion were somewhat summarized, attributing the hazards to bombardments [from WWII] and declaring the urban center of the city to be in the greatest danger, conditions that could only be corrected, in their opinion, by demolition and reconstruction. In particular, the commission said that disturbed conditions in the subsoil caused by the bombing could make it particularly dangerous for residents the following areas:

a)
a 60-meter-wide strip along the axis of via Formale, via S. Matteo,
via Trinità degli Spagnoli, following almost a contour line to the ex-Gradoni [steps] di Chiaia. That strip is over the path of an ancient Greco-Roman aqueduct;
b) zones of lesser interest: halfway up the Stella rise, via Nuova Capodimonte, and via Cagnazzi;
c) potential hazardous areas: vico S. Caterina a Formiello, the street and square of S. Giovanni a Carbonara;
d) the decumani [east-west streets] of Greek Naples: S. Biagio dei Librai, via Tribunali, and via Anticaglia;

The next two images on the right, 142 and 143, respectively, are both of the collapse of the
retaining wall and resulting collapse of the roadway on via Catullo (March 1966)

image 142                  
Furthermore, the commission acknowledged that the main cause of the disturbances to the stability of building was water in the subsoil made worse by preexisting empty spaces. They proposed investigating the flow of such water, taking a census of all the empty spaces in the subsoil, putting a sewerage code into effect and collecting underground waters even at some distance away in order to prevent infiltration into the subsoil of the urban center. Two studies remain to be mentioned: those done by the newspaper Il Mattino, specifically:

4) The Report of 1931-32 came after numerous collapses and cave-ins. The task: collect data to establish the location and distribution of all such spaces in the subsoil; keep aqueducts and sewers under observation; give proper weight to the importance of road conditions, which are often precursors of collapses due to flooding of terrain or to other underground movement in the soil.

5) The Report of 1961-62 called for: collecting data on underground cavities; mapping the subsoil; inspecting all hazardous buildings; checking the aqueducts and sewers to verify their efficiency; regulating subsoil public services; issuing building licenses only after documentation of studies done in the foundation terrain.

From that, we see that some causes of movements in the subsoil are agreed upon and others are only occasionally cited. It was generally agreed on that there are furthercauses, at least as to particulars. In picking up the threads of this discussion here, we have used statistical criteria that lend themselves to distinguishing regular episodes from occasional ones.

To that end, we have considered the statistical investigations done: by the Municipal Administration for 1889-92; by R. De Stefano, R. Allocca, and F. Tagliartela for 1951-1961; and by a working group under the auspices of the Italian Geotechnical Association, which concerned itself with the problems of the subsoil of Naples for a presentation at the VIII National Geotechnical Congress. This working group conducted two separate investigations, one of which was done using archival news reports of Il Mattino for the periods 1930-39 and 1951-61; the other investigation was on the basis of material in possession of A.M.A.N. (Azienda Municipalizzata Acquedotto di Napoli) [Municipal Aqueduct Authority of Naples] for the period 1918-65.

Unfortunately, the criteria used in these studies were not the same; they also used different sources; thus, the results mean different things. Particularly, we note that the first two studies were done, respectively, (1) on the basis of information provided by the builders, themselves, and (2) on the basis of reports in the possession of the Municipal Technical Office for Public Safety. The latter take into account even the slightest soil movement and are useful for showing how the conditions of buildings change as you move from one part of the city to another. The other two investigations were done, respectively, (1) using archival material from Il Mattino, and (2) using documentation from A.M.A.N. Those two studies limit themselves to episodes of movement that caught the attention of public opinion or caused economic damage of a certain importance and, thus, give some indication that conditions in the subsoil may actually affect the stability of buildings on the surface.

We can call the latter grandi dissesti [large movements] and the former piccoli dissesti [small movements]. The first two studies include both but emphasize small movements; the other two focus on large movements. If we compare statistics from all four of the studies with some data from earlier periods, we can draw some conclusions about the main causes of movements in the subsoil and how that has evolved.
image 142                                      
A first conclusion is how both kinds of movement have been influenced by construction at the end of the 1800s of the Serino Aqueduct and the new city sewerage system. Comparing relevant statistics from 1889-93 and reports of soil movements before that time, we conclude that the construction of the new aqueduct and sewerage system —although they did cause episodes of small movements— were not the primary cause since such episodes had been reported all around the perimeter of the city well before that period. The same construction, however, had a greater influence on the incidence of large movements, which, although not totally lacking in the past, must have been much less frequent since there are only rare reports of them.

Another conclusion from a comparison of the same statistics from 1889-93 and the years following show the influence of the Risanamento [urban renewal, 1885-1915] on episodes of small soil movement; movements were more frequent when all the construction was going on and diminished afterwards. Proof of that is the fact that in the oldest surveys the Vicaria section was second only to Montecalvario in frequency of episodes of small movement; later surveys show it to be almost in last place.

There is no doubt that many of the episodes of small movements in the area of the Risanamento were due to the great age of some of the buildings and the type of structures they were. Continuing to compare the evolution of small soil movements over time, we note that such episodes are not reported in the data of the 1934 Commission
of the Engineers Union of Naples, which blamed the movements on the disordered and chaotic secondary services in the subsoil. Nor are they reported by the Municipal Commission of 1956, which put most blame on damage from bombardments in the last war. In comparing the statistics from 1889-93 with the most recent ones, it does not seem that episodes of small movement in the subsoil have increased from then to now.

Also, in comparing pre-WW2 statistics from 1930-39 with those from 1951-61, we have not found anything that would let us say that wartime bombings had any notable effect on episodes of subsequent soil movements, large or small, in the city. Incidentally, we note that the statistics compare 1930-39 with 1951-61 and seem to have excluded willfully the immediate post-war period. Similarly, we conclude that just as with wartime bombings, the 1930 earthquake did nothing to alter the frequency of such movements except perhaps for a short period of time. In the same fashion, at least as far as large movement goes, we maintain that the rapid increase in heavy traffic has not been a determining cause.

Considering the evolution over time of the phenomenon, we can say that of all the things that have changed the environment over the last 80 years and might be listed as causes of the movement of houses, streets and secondary services, the most important one was the construction of the water distribution system and the sewerage system. Other causes have been secondary. That main cause has been responsible for the increase in small soil movements and, importantly, the cause of large ones.


image 135: Street cave-in on via Posillipo
(Nov. 1957)

Considering now how the phenomenon of soil movement has spread in the city, we can compare data gathered at different times and from different zones and look at the severity, case by case. The zones of most recent expansion are in the west. The above-mentioned statistics do not consider those areas, and we shall consider them separately, below. More centrally, however, the zones in which there has been a greater frequency of movement, both large and small, are always the same: the quarters of Stella, Avvocata, Montecalvario and S. Ferdinando, which follow one another more or less in a continuous strip along the slopes of the Capodimonte and Vomero hills.

The reasons for movement, large and small, are thus to be looked for either in features that might make those zones different from others in the city or in the fact that only in those areas do certain circumstances conspire to work together. Having said that, we have to look at the environmental factors in those areas. The areas are, as noted, along the great tuffaceous mass that is the framework of the hills. Loose materials cover that mass in varying degrees of thickness. Surface terrains and tuff substrata are notably sloped; the underground aquifer is deep; the many cavities dug by man for one reason or another break the continuity of both the materials on top and the mass below; the buildings are mostly old and the streets have old paved surfaces of basalt. None of those factors, however, individually, can explain the phenomenon of movement in the areas we are talking about.

The mechanical characteristics of the terrains —not just of the lapideous tuff formations, but also of the loose materials on top— are in themselves favorable and, in any event, no worse than those of subsoils in other large cities. We might, however, add that the tuff mass does have occasional and extended fractures, and there are cuts in some steep walls that can, in fact, detach dangerously and unpredictably. In turn, the loose materials on top are sensitive to water; that is, they settle notably from simple imbibition (or absorption) of water, which can cause erosion and, in the presence of a notable hydraulic gradient [a steep slope], set up a true siphoning effect.

On the other hand, with the methods of calculation now at our disposal in terrain mechanics, we see that the loads transmitted to the terrains by foundations of buildings —foundations of any sort— are totally compatible with the mechanical characteristics of those terrains except where there are anomalies of imbibition or underground erosion. Indeed, experience has shown us that in most cases foundations do not give way because of the earth beneath them
but rather from defects or material fatigue in the foundations, themselves [emphasis added].

The areas we are talking about have the greatest number of cavities in the tuffaceous banks (see chapter IV of part 2), but even that is not in itself a danger from a purely static point of view. Parts of walls or vaults may occasionally detach, yes, and that does reduce the stability of the space. That has happened only in very exceptional cases because of a load transmitted from the surface. Finally, the age of the buildings may be a contributing factor in the cases of small movement in the buildings, themselves, but that alone doesn't account for the increasing frequency of both small and large movement in these areas. There are equally old buildings in the ancient parts of Naples, where the phenomenon of movement is much less noticeable. It can thus only be the cumulative effect of all of the above factors in these areas that combine to produce this plague of subsoil movement, collapses and cave-ins.

So on the one hand we have the aquifer at great depth and, on the other, the considerable slope of the terrain and the widespread presence of various forms of cavities. Together, that allows water to infiltrate into terrain above the tuff, terrain that initially will not saturate because of its great thickness but which may eventually move because of imbibition in the terrain and, with notable hydraulic gradients, can cause serious internal erosion.

We thus have in the terrain continuous episodes of small movement that, at least for the most part, are to blame for the progressive deterioration of older buildings and infrastructure. If, however, there is a break in a line from the aqueduct or in a sewer, or if a sewer line is overloaded, that increases the amount of water seeping into the terrain and gives rise to a real siphoning effect and some of the phenomena described thus far. That may cause collapses and cave-ins. In any event, it compromises the stability of structures on the surface. In most cases, then, either the infiltration of water into the subsoil is the primary cause of cave-ins and collapses, or such mishaps represent the last in a series of prior episodes that may not have been immediately evident on the surface but which created the conditions for the subsoil to move.
image 144:                              
street cave-in on via Cortese all'Arenella
(Sept. 1967)                           
We see an easy and convincing interpretation of such phenomena. In practice, however, their evolution is quite complicated as seen from the endless legal battles caused by these episodes of subsoil movement, battles that often revolve around trying to reconstruct after the fact exactly what happened. It is difficult to say that the first bit of water that seeped into the soil, or the first incident of soil settling, was the result of a break in a pipe from the aqueduct or in a public or private sewer. Perhaps those components were initially sound and never would have leaked at all unless set upon by water from another source. It is difficult to say whether the initial cause of siphoning in the subsoil is a line from the aqueduct or sewer or even a drain-pipe running alongside somewhere. Except in exceptional cases, once siphoning has occurred, the aqueduct lines, sewer lines and secondary pipes will all have been so badly damaged or even destroyed that reconstructing the event is impossible.

At the most, we can say that small leaks in the aqueduct or sewers can lead to small movement; large movement, on the other hand, will occur in cases where breaks in the aqueduct or in sewers are not swiftly repaired or where a run-off sewer overflows and large amounts of water are allowed to flow through steep gradients, letting the water actually carry material away. It is obviously impossible to keep any water at all from getting into the subsoil. It is equally impossible to get rid of the cavities, large and small, that exist in the subsoil. Consequently, in order to keep water from infiltrating from the surface and from moving through cavities with notable hydraulic gradients and cause erosion and siphoning. We can only put the strata in order that are closest to the surface and create an effective drainage system between street level and the sewers such as to intercept and move the water into the sewers.

Aside from the practical possibility of such a project, it is evident, without singling out a particular cause (as was the case with the 1934 commission of the Engineers Union) that there is extreme disorder beneath the streets. Various services are at work down there; they work independently of one another and often get in each other's way. This, too, is a cause of movement in the subsoil. Similar phenomena have occurred elsewhere in the city. Not all of the contributing causes, however, are present in those areas the way they are in the areas along the hill slopes. Those other areas thus have fewer episodes of movement; importantly, they have fewer episodes of large movement.

In those areas where the aquifer is just a few meters from the surface (S. Giovanni a Teduccio, Barra, Ponticelli, Poggioreale, S. Anna alle Paludi, Borgo Loreto, Vasto, Via Marina and the Rettifilo) there are no underground cavities. There is thus no possibility that water seeping into the subsoil can be absorbed by thick strata of initially unsaturated terrain, so movement there is limited and less serious if it does occur. Damaged buildings can generally be restored except in the presence of structural deficiencies such as foundations not resting on a solid base, or insufficient load-bearing sections in walls, or material fatigue, etc. Static* equilibrium can be reestablished by normal work beneath the foundation and wall consolidation.
[*translator's note: in the mechanical sense "static" meas acting through weight only, said of the pressure exerted by a motionless body or mass. Static is the opposite of dynamic. Thus, if a solid wall is resting against or on solid ground but threatening to topple over, "restablishing static equilibrium" means you can "keep it from falling over."]

In that regard, we note that the buildings with traditional ordinary cement foundations (Vesuvian scoria, pozzolana del Campo, hydraulic lime) did not move at all during the risanamento [urban renewal 1885-1915] along the Rettifilo-via Marina strip. A few of the foundations in the Vasto quarter were insufficiently thick or did not rest on a sold base; they had to be rebuilt, after 50 years, but still with traditional methods of restoration.

Finally we note that filled-in river beds (Vergini, Arenaccia, Lavinaio, Toledo, etc.), except in some rare and well-defined cases, have not caused notable mishaps.There have been serious episodes of soil movement even in some areas where the aquifer is near the surface. That happened along the route of the Metropolitan tunnel between Piazza Cavour and Piazza Garibaldi as, during construction, the aquifer dropped artificially, which tallies with what we said earlier.

Recent urban expansion deserves separate comment, particularly in those areas on the slopes of the Vomero and Posillipo hills. The morphological characteristics and the nature of the terrain are similar to those described for Stella, Avvocata, Montecalvario, and S. Ferdinando. The unbridled race to put up new building as well as new options offered by recent methods of construction, however, have led to a terrain architecture that employs very high terraces and embankments even in the older sections. Furthermore, private initiative, acting ahead of public planning, has prevented the orderly layout of streets and sewer lines. The sad result of this has been the rapid deterioration of road surfaces, the equally rapid deterioration of public and private sewers, the increasing frequency of breaks in water lines, and a series of collapsed streets, caved-in sustaining walls, and earth slides.

Some of these things, such as detached fragments of tufo or slides along banks of pozzolana can be attributed to particular geological conditions and are not easy to predict. Other mishaps, such as cracks in and collapses of old retaining walls halfway up the slopes have been caused by the increase in the amount of traffic and also by the nature of heavier vehicles. Other incidents, just as they have occurred in older quarters of the city, have happened here because of the infiltration of water, made all the more frequent because new sewers are too small or old sewers can't handle the increased load. As a result, they overflow even when rain is not intense. In most cases, however, ruptured streets or collapsed walls are man-made and are traceable to
bad planning or a lack of respect of ordinary construction norms.

Indeed, except in cases where streets rest on landfill thrown in helter-skelter, little effort is made to ensure that even the strata of properly mined pozzolana beneath roads have been properly packed down. As a consequence, in spite of the use of abundant terrain with good mechanical properties, with the passage of time and under stress, streets break up and rupture their otherwise impermeable surfaces. The phenomenon accelerates from breaks in the impermeable surface to localized cracks caused by passing traffic, such that the very sewers meant to channel water properly away from the surfaces become damaged
themselves and contribute to the problem of infiltration. The seeping water looks for a way out, finds it, and moves towards it, thus increasing erosion and movement in the subsoil. In some cases, the street, itself, winds up suspended over a void and survives only because it has found some way to stay in place as a kind of "bridge." All it then takes sometimes is for single vehicle to pass over it, and it
can collapse. Sometimes  the earth slide is the last in a series of incidents leading up to true siphoning.

image 145                    
   street cave-in, via A. Falcone
(Sept. 1967)                

It is quite different if the water seeping in doesn't find a way out. It will "imbibe"  —be absorbed— into a much wider area. Where that occurs, the soil characteristics, themselves, are altered, and hydrostatic forces arise that were not foreseen during the original planning. [note: A standing body of water pushing against the wall of a damn is an example of hydrostatic force.] That can cause retaining walls to collapse. In that kind of collapse, it is more commonly the case that even if the filler material in back of the wall was properly laid, the wall itself was not sound and might have collapsed anyway. In most cases, we find that such walls were of the "build-as-you-go" variety or built to antiquated standards. Even in modern construction we haven't found many cases where a serious investigation was done beforehand, whether in calculating values for terrain characteristics or for setting values for safety standards supposedly based on those values. Human guilt is increased if we consider that many of the episodes that have occurred were preceded by warning signs that no one paid attention to.

Before concluding, we should consider a particular kind of mishap —the ones that have happened in tunnels. A number of tunnels built recently in Neapolitan yellow tuff, either during construction or shortly after being completed, displayed notable signs of movement, which is why they had to be reinforced. For example, we note the tunnel beneath the Posillipo hill, [now] called the Quattro Giornate Tunnel (formerly the Municipal Tramway Tunnel). It was opened in 1884 and closed in 1890 because of cave-ins; also, the Diretissima Naples-Rome [train] tunnel, tested in 1917, had problems and was closed in 1922, was under repairs until 1925 and had more problems in 1931; the Laziale tunnel, finished in 1926, after numerous incidents of movement during construction showed additional damage in 1932. All of these cases displayed longitudinal lesions along the crown or crushed support columns. Similar mishaps have occurred recently in the Circumflegrean [train] tunnel that passes through the Vomero hill; it was finished in 1954 and is currently under repair.

Tunnel collapses and earth slides are not always that easy to explain. On the one hand, we note that theories of homogeneousness and isotropy*
are at the basis of calculations to build tunnels, but those theories are not always verifiable when working with tuff. That is because of the particular origins of the material. An average bank of tuff can often display notable point to point variations in mechanical characteristics without any change at all in outward appearance. Even during excavation, it is practically impossible to notice the variations. That is not even considering that fissures and cracks can open in the material during excavation but stay hidden beneath the excavated surface, which can alter considerably the load-bearing characteristics of the material.
*[homegeneous: having the same or similar characteristics or qualities.
  isotropy: when plasticity or conductivity are the same no matter where you measure.]


But even if the theories of homogeneousness and isotropy are totally verified, analysis of stress in the tuff masses in each of the tunnels just mentioned has shown that the load on the columns and crown was greater, respectively, than the resistance to compression and traction of the tuff. In the absence of adequate calculations of stress, we have to look for a cause behind the mishaps during excavations of tuffaceous rock in the tunnels.

In that regard, we note that the internal covering on the surfaces of the tunnels was put in some time after the completion of the tunnels and cannot have reduced the tension in the rock, a phenomenon that is noticeable the moment the digging is finished. On the other hand, in the case of some of the tunnels mentioned, internal covering is almost absent (for example, the Circumflegrean tunnel was lined with 40-cm-thick tuff blocks for the sole purpose of
making the surfaces regular. We thus hold that in order to avoid analogous mishaps in the future, tension in the surrounding tuff mass has to be maintained within permissible limits.

In summary, both small and large movements in the subsoil of the city can be attributed to a variety of causes, only some of which have to do with the make-up or structure of the subsoil, itself. More often, causes are man-made. First, we can say that the loose terrains in the subsoil are particularly sensitive to water; the terrains settle notably through simple imbibition and are subject to internal erosion as water moves through them, particularly where hydraulic gradients are steep. That characteristic [of sensitivity to water] assumes great importance when the aquifer is deep and there are many cavities of various sizes either in the loose terrains or in the tuff substratum, which is, in fact, the case in a large part of the urban territory.

As far as man-made factors go, from statistical studies we see that these factors are diverse and of varying degrees of importance in those parts of the city that go back to before the recent post-war wave of urban development. We see that in the oldest pasts of the city, there have always been episodes of small movement, while large movement, with some exceptions, have their beginning with the construction of the Serino aqueduct and the modern sewerage system. The small mishaps have had to do with the fact that the houses in the Naples of old were not built to withstand the slightest settling of a foundation caused even by a minor episode of water seeping into the subsoil. With time, the aging buildings had the added stress of such modifications as add-on rooms and even entire floors on top of the original roofs, often with no technical criteria.

Episodes of large movement in the subsoil, on the other hand, have had to do with significant and concentrated emissions of water from breaks in the aqueduct or sewerage system. The situation is somewhat different in the areas of recent expansion in the city, particularly on the Vomero and Posillipo hills. There the cases of small movement are relatively rare, which is explained by the fact the newer buildings are structurally sounder and built to withstand
even appreciable movement in the subsoil.

More frequent, however, are those cases of great movement that opens sink-holes in streets, causes cave-ins, and collapses retaining walls. From one viewpoint, the causes are in the infrastructure, which has been rapidly more and more insufficient in the face of the speed and intensity of new construction. As well, though, there has often been improper planning and excavating for embankments, terracing, and retaining walls, which is most important here since it often has to do with development in the hill areas.

In those areas of recent urban development, further episodes of small and large movement in the subsoil are, unfortunately, to be expected. We can't reasonably expect that they will not happen, even if the provisions that this Commission shall recommend to the Administration are adopted and carried out as rapidly as possible. It is clear,
however, that if we put it off and don't start on some of these provisions, perilous conditions in the city can only get worse. With that, we are saying that all plans for urban development and construction in Naples have to be regulated by a uniform plan for urban safety.

END OF CHAPTER 9    END OF PART TWO OF THE SUBSOIL OF NAPLES   Oct. 30, 2019

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