Conference PaperPDF Available

Landslide hazard and risk along the campanian roads (Italy

Authors:
Géoline 2005 – Lyon, France – 23rd - 25th, May/Mai 2005
Landslide hazard and risk along the campanian roads (Italy)
BUDETTA, P., DE RISO, R., SANTO, A.
Department of Geotechnical Engineering, Section of Applied Geology, University of Naples
“Federico II” Piazzale Tecchio, 80, 80125 Napoli, Italy
budetta@unina.it; deriso@unina.it; santo@unina.it
Abstract
This paper presents the main landslides typologies affecting routes in several geological
environments of the Campania region (Southern Italy). Statistical data coming from the A.V.I.
(Aree Vulnerate Italiane) catalogue during the period from 1950 to 2001 are presented.
Comments concerning the landslide hazard and risk along some important routes have been
included.
Keywords: Landslide hazard, landslide risk, roads, Campania
Introduction
Campania is one of the widest regions in Italy (about 13,600 km2) and its density of population is
also very high. Many towns and villages are large and densely populated and the road system is
consequently just as dense and branched. Some of the roads date back to the Roman age and
were part of ancient consular routes connecting the city of Rome to the Apulia region (via Appia),
to the Phlegrean Fields (via Domitiana) and to Calabria (via Popilia). During the 19th Century
more roads were built by the Bridges and Roads Bourbon Department, in order to link Naples,
which was the main city in the Reign of the Two Sicilies, to Sorrento and Amalfi (the Surrentine
and Amalphitan roads), to
Caserta and to the Adriatic
coast. The major traffic
development that
characterised the second half
of the last century caused a
large scale expansion of the
regional road system. At
present, the national Company
which owns the roads (ANAS)
and other Regional Traffic
Departments take care of
about 9,500 kilometres roads
in length, including motorways,
national, regional and
provincial roads (Fig.1). Also
very dense is the byroad
system.
The Campanian
geomorphologic layout
includes two wide Thyrrenian
coastal plains (Piana
Campana and Piana del Sele)
and some intermountain plains
where alluvial and detrital-
pyroclastic deposits outcrop
(Fig.1). A rough relief is a very common feature along the Apennines Chain that occupy most of
the regional area. The Apennines are a NW-SE trending Neogene and Quaternary thrust and fold
belt. Since the late Pliocene, following the opening of the Tyrrhenian sea, extensional tectonics
progressively shifting to the East have produced a number of deep tectonic basins, hosting
mainly marine and volcanic
Figure 1. Geological map of the studied area and typological
distribution of regional road system
Géoline 2005 – Lyon, France – 23rd - 25th, May/Mai 2005
deposits on the Tyrrhenian side (Phlegrean Fields, Ischia, Monte Somma-Vesuvio). The highest
peaks appear along calcareous-dolomitic Apennines (Monti Matese, Picentini, Alburno-Cervati)
where sometimes the carbonate bedrock is mantled with volcanoclastic deposits generally 2-4
metres thick. Gentle hills with smoother morphologies are prevalently situated along the eastern
flank of Apennines Chain. Here silico-clastic deposits, calcareous-marly and arenaceous-clayey
flysch, conglomerates as well as sandy-clayey deposits outcrop (Fig.1). An active seismicity
showing that the quaternary neotectonic movements are still in progress affects some regional
areas (Irpinia and Sannio). Recent studies confirm that the present-day tectonic setting of the
Southern Apennines is guided by a system of Quaternary normal faults, which determine a still
immature basin-and-range morphology. These faults are responsible for frequent moderate to
strong earthquakes, with typical hypocentral depths of 7–20 km (Amato et al., 1997).
Due to rough relief, geological and structural complexity and active seismicity of the region,
landslides affecting towns, roads and factories frequently occur. Sometimes this has resulted in
fatalities as well as in considerable damage and injuries. As far as roads are concerned, rock-
falls and debris flows are the most frequent phenomena affecting cuts and steep slopes
encumbering roads. Usually, these landslides involve small-sized masses but are very rapid
therefore they can cause injury and death to the users of the said routes. Highly fractured
calcareous and tufaceous rock masses are affected by rock-falls usually triggered by heavy
rainfalls and earthquakes. Instead, debris flows involve the volcanoclastic deposits outcropping
on very steep slopes formed by limestones. These landslides mainly affect the northwestern
Campanian region and are frequently triggered by heavy rainfalls, too. Slow earth flows, mud
flows and complex landslides (composite rotational slides – earth flows) involving big volumes,
affect more gentle slopes formed by arenaceous-marly and flysch deposits. Since such
phenomena usually display slow movements, they are less dangerous for motorists, but they can
cause traffic blocks and delays for long periods as well as severe damage to road structures.
Regional roads and
landslides
Data concerning landslides
along the regional road
system were extracted from
the A.V.I. (Aree Vulnerate
Italiane) catalogue (CNR-
GNDCI, 1998; 2004). This
catalogue is the most
complete Italian data-base
and now it is the only
available regional catalogue
containing information about
landslide/road interactions.
During the period from 1950
to 2001 the Campanian road
system was affected by 814
landslides. The available data
show that about 54% of the
landslides involved the byroad
system, about 19% the
provincial roads and about
27% the national roads and
motorways. Regarding the
landslide distribution per year
it’s possible to observe a larger
amount during high rainy
periods or strong earthquakes
(1954 Salernitan inundation, 1968, 1980 Irpinia earthquake). There has been an increase in
landslides from 1991 onwards because there were more frequent stormy events involving wider
areas (for example 1997 Campanian inundation, 1998 and 2000). The increase in landslides in
the 10 year-period from 1991 to 2001 is possibly due to the significant catalogue improvement
where also small events that usually were not carried in the past were noted. About 250
landslides happened in January 1997 during heavy rainfalls involving wide regional territories and
Figure 2. Landslide density along some important roads and
localization of the reported casualties. The asterisks show
the studied localities.
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causing 9 deaths along the roads. With reference to the mentioned period, the recorded
landslides caused 64 casualties and about 102 injured road-users (Fig. 2 and 3). Even though
many landslides happened from 1998 onwards, the fatality rate per year has not significantly
increased. In the last 4 years there were only 2 deaths and the average annual fatality rate is 0.5.
The landslide density along regional roads is very variable due to local geological and geo-
morphological layouts, hydrologeological and human factors, etc. Some roads, prevalently
located in mountainous areas, show
landslide densities up to about 0,9
landslides per kilometre; a mean value is
about 0,3 landslides per kilometre (Fig.2).
But it is necessary to observe that there is
inadequate documentation of the landslide
activity for most roads, due to the fact that
the companies managing those roads
often omit to report minor events; in fact
that would involve extra costs for the
personnel and monitoring equipment for
the collection of the data. Therefore,
events that are not considered life
threatening or significantly damaging
usually are unreported.
This particularly occurs along the inner
regional road system involving the
slopes along the eastern flank of the
Apennines Chain. Here many landslides present slow movements and there is little traffic on the
roads. The available data display that some municipal territories are affected by recurrent
landslide typologies or reactivation of suspended events, prevalently along roads passing
through meso-cenozoic flysch (Unità irpine, Flysch del Cilento, Argille varicolori) outcropping in
the inner part of the Apennines Chain.
Figure 3. Cumulated number of landslides and
correlated deaths and injuries during the
mentioned period.
High vulnerability affects many urban districts of Naples and surrounding areas (especially
Phlegrean Fields) where numerous but small slides happen to cause high risk conditions. These
areas rest on old volcanic piles and the lithostratigraphic layout is characterized by tuffs (“Yellow
Neapolitan Tuff” and “Gray Campanian Tuff”) and lavas alternating to loose or pseudocoherent
pyroclastic deposits (sandy-silty volcanic ashes, residual clayey soils from old volcanic ashes and
pumiceous strata) derived from volcanic activity of the Phlegrean Fields. Sometimes, buildings
and roads are close or at the base of old open quarry cuts from which tuffs for masonries were
mined in the past. For roads concerning the Neapolitan area, the A.V.I. catalogue reports about
152 landslides during the mentioned period. Rock-falls involve fractured tuffs prevalently
outcropping along old cuts and steep slopes whereas sudden translational slides and slide/flow
affect more gentle slopes (generally between 35° and 40°) characterized by pyroclastic deposits
with low values of shear strength (Calcaterra and Guarino, 1999). But it’s necessary to point out
that some informations reported as landslides by the A.V.I. catalogue in fact are sinkholes due to
sewer system failures along urban roads or wall failures.
Landslide hazard and risk along roads
Landslides along roads are hazardous in several ways. The first type of hazard regards the
moving or stationary vehicles being hit by landslide debris. The second type of hazard regards
the moving vehicle that could collide with a landslide debris previously fallen on the road. Third, a
landslide debris could block the traffic flow causing delays, damages and considerable repairing
costs (Bunce et al., 1997). Hazard evaluation is still a highly complex process requiring an exact
assessment of the triggering mechanisms, the run-out parameters (maximum distance reached,
flow velocity, thickness and distribution of deposits), the vulnerability of the roads placed at the
foothill and the type of vehicles (Pierson et. al., 1990; Budetta, 2002). Vulnerability depends on
several factors connected to the type of vehicle/landslide deposit interaction, including the vehicle
speed and length, the available decision sight distance, the traffic volume, the length of the
landslide risk section of the route, the number of occupants in a vehicle and the type of vehicle.
Landslide risk can be interpreted as expected losses of lives, people injured, damaged road
structures or disrupted economic activity. Referring to routes, the ‘‘risk to life’’ [probability of death
in the population exposed to the hazard for 1 year, P(D)] due to the landslides is the annual
probability of an accident involving the death of one or more occupants of a vehicle. P(D) is given
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by the product of the annual probability of land-sliding, the vehicle being spatially in the path of
the event when it occurs, the vehicle being temporally in the path of the event when it occurs and
one or more occupants of the vehicle being killed as a result (adapted from Morgan et al. 1992).
Because of the numerous and complex variables involved, some attention to this matter has
been given only lately in the international literature (Bunce et al., 1997; Guzzetti et al. 2003;
Baillifard et al. 2003). Subsequently, some case histories regarding the main Campanian routes
are explained. These examples mainly concern the fast movements (debris flows and rock-falls)
because of their high frequency and imposed hazard. Finally, some case histories regarding slow
movements are presented explaining the road instabilities of the inner part of the Apennines
Chain.
The debris flows of St. Pantaleone hill
St. Pantaleone hill, located in the province of Salerno, is a small limestone hill rising 200 m above
the surrounding alluvial plain where Pagani and Nocera Inferiore are situated (Fig. 4). Its northern
slope (approximately 0.17 km2) is an old fault scarp striking N60° and dipping about 37° (De Riso
et al. 1999). The double-lane motorway A3 (Naples - Salerno) is located at the foothill and was
built about 40 years ago, half-way up the hill. The section exposed to debris flow hazard is
approximately 890 m long. On the slope, cross-bedded limestones/dolomites outcrop, dipping
about 15°east – north-eastwards, overlain by volcanoclastic materials. These materials mantle
the slope with thicknesses ranging from 1 m (at the top) to 15 m (at the bottom). The pyroclastic
deposits are characterised by sandy-silty volcanic ashes, residual clayey soils from old volcanic
ashes and pumiceous strata derived from historic volcanic activity of the Phlegrean Fields and
Mount Somma-Vesuvius.
Figure 4. Engineering geomorphological map of the St.Pantaleone hill. 1 Landslide debris
(actual); 2 pyroclastic deposits (Holocene); 3 remolded volcanic ashes (Holocene); 4
limestones and dolomitic limestones (Cretaceous); 5 active landslide crown; 6 relict landslide
crown; 7 channel erosion; 8 main scarp; 9 groundwater egress; 10 geological cross section
trace
(
b
y
Budetta
,
2002
)
.
Due to poor consolidation of the pyroclastic deposits, the high/steep slope and the hazard posed
by the ease of detachment of these deposits from the underlying limestone bedrocks, the
likelihood of mobilisation of the material as debris flows is high. In fact, the northern slope of St.
Pantaleone hill has been characterised by successive complex landslides (debris slides/debris
flows) and well-documented information is available regarding landslide activity over the past 40
years. Older historical sources contain references to landslides dating back to the first half of the
nineteenth century. In 1960, two simultaneous debris flows occurred within a distance of about
150 m, but thanks to the absence of traffic, no one was hurt. In 1972 another failure occurred
near the toe of a rocky cliff. The impact of a vehicle with the landslide deposit obstructing the
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southern lane of the motorway caused the death of a user of the motorway. In 1997, a new
debris flow occurred along the slope. Near the main failure area, the pyroclastic deposits were
only some 0.5 to 1 m thick. The zone
of failure appeared to be in the
pumiceous strata from the 79 A.D.
eruption of Mount Somma-Vesuvius.
The area affected by this debris flow
stretches down-slope over 8,000 m2;
the landslide deposit involved 4,500
m3. As in the 1972 event, the
landslide deposit came to a halt on
the motorway below. Three cars
crashed into it and one of the drivers
was killed. For these reasons, the
section of the motorway exposed to
debris flow hazard has been studied
in detail in order to establish the level
of risk to life (Budetta, 2002). The following assumptions have been made: the death probability
is calculated only for accidents caused by the direct impact of a moving vehicle on landslide
debris (moving vehicle/stationary deposit interaction). The chance that more than one person
could be present in the car during an accident is not considered. It is assumed that traffic is
uniformly distributed in time. Adopting the ‘‘event tree analysis’’ (Fig. 5), the annual probability of
one fatality occurring in the population exposed to the risk in the entire debris flow risk section is
1,42x10-3 (Budetta, 2002). This value is generally consistent with landslide mortality rates for
Italy. Referring to the catalogue of historical landslide events that have caused loss of life,
missing people, injuries and homelessness in the twentieth century, Guzzetti (2000) pointed out
that Italy has the highest cumulative number of deaths or missing people and the highest
expected yearly losses of life in Europe.
Figure 5. Event tree at St. Pantaleone hill (by
Budetta, 2002).
The annual frequency of landslides that result in fatalities exceeds 1 for low-impact events ( 3
deaths) and is about 10-3 for events that result in hundreds of deaths (Guzzetti 2000). Because
the estimated risk to life calculated for the St. Pantaleone hill is unacceptable, in 2001 the
motorway-owners built passive protection works (i.e. barriers and debris-breaks walls) as well as
a protection gallery along the entire section of the motorway exposed to debris flows risk.
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Figure 6. Oblique aerial
view of the 1997
Pozzano landslide (by
Calcaterra & Santo
2004).
The Pozzano landslide
On 10th January 1997 a landslide started in the Pozzano area, from about 440 m a.s.l.. (Fig. 6).
After a J-shaped travel, the landslide struck a private house located at the right side of the foot
zone, killing 2 of the inhabitants. Then it reached the motorway n.145 (Sorrentina), where several
vehicles were in queue: this coincidence was due to a precautional road interruption, as another
landslide occurred a few hundred metres eastbound. Consequently, this caused the loss of other
2 human lives. Finally, the mass reached the underlying shoreline, still moving away into the sea
for at least some tens of metres (Calcaterra and Santo, 2004).
The Pozzano landslide involved the pyroclastic cover overlying the Cretaceous carbonate
sequence. The large-scale survey allowed to distinguish several geological units: in the
detachment area, 3-4 m of yellowish-brown altered pyroclastics have been mapped, referable to
eruptions from Mt. Somma–Vesuvius. In the initial detachment zone, the pyroclastic cover is
discontinuous, for the presence of two orders of calcareous cliffs, 5-10 m high, due to selective
erosion (Fig. 7).
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Figure 7. Geomorphological
map of the Pozzano
landslide.1) Area of initial
detachment and sliding; 2)
Channelized flow zone; 3)
Upper landslide body; 4) Lower
landslide body; 5) Submerged
landslide body (inferred); 6)
Relict rock fall body, older than
39.000 yrs. BP; 7) Calcareous
cliff; 8) Crown area; 9) Flow
direction; 10) Zone of
bifurcation of the landslide
body; 11) Tension crack in the
pyroclastic cover; 12) 1997
All over the upper portion of the landslide area, several remnants of a pumice level have been
mapped, 70 cm thick, made of 3-4 cm whitish elements: these features allow to refer the whole
level to the well known 79 AD Vesuvius eruption, which destroyed Pompeii and Herculaneum.
The pumice level tends to become discontinuous in the middle-lower portion of the landslide
channel. A first, small landslide detached from the edge of a pathway running at about 440 m
a.s.l.; here, weathered, fine-grained epiclastics crop out on a steep slope (45°). The initial crown
has a total length of about 10 m, the surface of rupture is 5 m deep and the mobilized volume can
be estimated in about 500 m3. The initial landslide started as a rotational slide. This first landslide
body has then undergone a sudden acceleration, with a jump-and-fall effect, due to the
underneath sub-vertical calcareous cliff, after which an impact occurred on a gentler slope (37°),
where pyroclastics overlie a pumice level. Consequently, the “main” landslide was triggered,
showing features of a translational slide. The sliding over the pumice level lasted for at least 300
m, involving 3-4 m of pyroclastics. In the middle portion, the landslide channelled into a pre-
existing hollow. Here, the displaced mass, already disrupted, started to flow. From this point
downwards, the mass movement passed into an extremely rapid debris flow and mobilized a
large part of the deposits resting within the hollow; here the landslide channel is 40m large and
6m deep. The highly fluid material, governed by the centrifugal force, has ridden about 40 m over
the left flank of the channel, immediately upslope of a quarry (Fig.7).
Some tens of metres down-slope, the mass was divided into two parts by a small calcareous
ridge. The western portion of the mass (about 15.000 m3) reached the quarry and a part of it filled
the quarry for a length of about 120 m. The remaining part invaded two tunnels actually
underway, situated at a lower elevation with respect to the quarry. The eastern tunnel has been
invaded for about 60 m, while the western one for 15 m: it can be stated that at least 1500 m3
accumulated into both the tunnels. The eastern portion of the mass continued its travel along the
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pre-existing hollow, partially destroying a house (Fig. 6). A first part of the debris stopped in the
landslide channel, covering the limestones with no more than 1 m of material. Another part of the
debris (about 10.000 m3) stopped over the motorway no.145 and over the beach underneath,
while the remaining part reached the sea moving away for about 50 m from the shoreline: this
further volume
was estimated in
about 8-10.000
m3. Summing up
the partial
volumes, the total
amount of debris
mobilized can be
estimated in
about 40.000 m3.
The rock falls
affecting the
national road
“Sorrentina”
High road cuts
and natural
outcrops above
the road generate
rock falls and
rock avalanches
(Fig.8) along
many road
segments of this
very important
tranportation
corridor (Budetta
et al. 1994;
Budetta and De
Riso, 1988). In
fact, the
Sorrentine road
(n° 145) is the
only linear infrastructure of the Sorrentine peninsula and support a very high movement as well
as tourist traffic. The road was built during the first decades of the 19th century by the Bridges
and Roads Bourbon Department. The former historical information reported by the chief engineer
of that period, refers to rockfalls that occurred in 1832 and 1838 during the road construction.
Other landslides occurred between the Pozzano and Scrajo villages in 1842 and then in 1951
and 1958. Recent and well detailed rockfalls are referred to the second half of the last century.
Figure 8. The rock avalanche of the “Cava Fontanelle” landslide, near
Castellammare
b
Budetta and de Riso
1988 modified
.
Many landslides affect the road segment near the Meta di Sorrento village (Fig. 9). This area lies
on the northern edge of the Sorrentine Peninsula which is a horst transversally oriented towards
the Apennine mountain range. The horst is made up of thick Mesozoic dolomitic limestone
sequences on which Miocene flysch has been preserved in small structural depressions:
Quaternary clastic deposits together with pyroclastics also crop out (Budetta et al., 1994). Road
cuts and natural slopes near the Meta di Sorrento village belong to a very long and high (about
100 m) fault scarp striking N280° and dipping on average about 50°; vertical or overhanging
slopes are not infrequent (Fig. 9). Limestones and dolomitic limestones outcrop with bedding
planes dipping about 15°- 20° west-northwest. The rockmass is very fractured and there are
many faults (at times with strike-slip lines) and joints most of which can be attributed to major
joint sets with a smaller number randomly distributed. A high traffic intensity affects the entire
section of the road where the posted speed limit is 50 km/h. The average daily traffic was
recorded between Meta di Sorrento and Bivio Schito, a distance of 10 km. During the year, the
average diurnal traffic is nearly constant (13700 cars per day) but in nocturnal winter periods it is
poor for the lack of tourism. About 80% of the traffic is represented by cars.
In order to assess the exposition to the risk associated with rockfalls, and to prioritize budget
allocations for maintenance and remediation works, the RHRS’s modified method was applied
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(Budetta, 2004). The Rockfall Hazard Rating System (RHRS) provides a rational way to make
informed decisions on where and how to spend construction funds (Pierson et al., 1990; National
Highway Institute, 1993). Exponential scoring functions are used to represent the increases,
respectively, in hazard and in vulnerability that are reflected in the nine categories forming the
classification. As this method contains all the elements regarding the rockfall hazard (slope
height, geologic character, volume of rockfall/block size, climate and presence of water on slope
and rockfall history) and the vehicle vulnerability (ditch effectiveness, average vehicle risk,
percentage of decision sight distance, roadway width), the resulting total score assesses the
degree of the exposition to the risk along roads (Budetta, 2004). In the modified method, the
ratings for the categories “ditch effectiveness”, “geologic characteristic”, “volume of rockfall/block
size”, “climate and water circulation” and “rockfall history” have been rendered more easy and
objective. The main modifications regard the introduction of Slope Mass Rating by Romana
(1985) improving the estimate of the geologic characteristics, of the volume of the potentially
unstable blocks and the underground water circulation (Fig. 9). Other modifications regard the
scoring for the categories “decision sight distance” and “road geometry”. For these categories,
the Italian National Council’s standards (Consiglio Nazionale delle Ricerche – CNR) have been
used (CNR, 1980). The method has been applied to both the traffic directions of the road near
Meta di Sorrento because the percentage of reduction in the decision sight distance greatly
affects the results (Fig. 9) As it can be seen from the scores recorded for seven cross sections
were ranked in order to identify the most dangerous slopes, the total final scores range between
275 and 450 (Fig. 10).
Figure 9. Slope Mass Rating classes (after Romana, 1991) and cross section traces (red lines)
for the modified RHRS method. Class I areas are absent (by Budetta, 2004).
Figure 10. Total scores recorded for the
seven cross sections along Sorrentine road
(by Budett, 2004).
The difference in the total final scores between Sects. 1 and 2 (in the direction towards Meta di
Sorrento) with respect to all remaining sections is mainly due to Decision Sight Distance (DSD).
In fact, the considerable reduction in the percentage of DSD for the two traffic directions greatly
affects the results.
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Also the categories Slope Height, Average Vehicle Risk and Volume of rockfall/Block size are
more sensitive with respect to remaining categories. The analysis shows that there is an
unacceptable risk and it must be reduced using urgent remedial works. It is to be remembered
that this modified Rockfall Hazard Rating System (Fig. 10) is a preliminary tool for mapping the
road risk assessment and then to allow more detailed investigations with geotechnical and
geomechanical stability analyses in dangerous areas.
Landslides affecting the inner part of regional territory
Arenaceous-marly or calcareous-clayey flysch prevalently outcrop along the eastern flank of
Apennines Chain taking up about 6000 km2 of regional territory. The eastern flank of the Chain
where Sannio and Irpinia areas are situated largely correspond with Neogene and Quaternary
thrust. In these areas outcrop thick meso-cenozoic and mio-pliocenic formations consisting of
closely layered strata made up of argillites, siltstones, limestones and micaceus sandstones that
were deformed, uplifted and folded during the Tertiary. In these areas and in Cilento region also
outcrop sequences belonging to “Cilento Flysch” and to miocenic flysch of the “Carbonatic
Shelfs”. The Cilento Flysch is a succession of 4500 m thick turbiditic layers of distal facies at the
base, changing into proximal units towards the top. Miocenic flysh take up the edges of the main
horst and perithirrenic graben (Valle del Sele) or in some tectonic basins (Valli del Volturno,
Calore, Sabato, Tanagro etc.).
Complex landslides or rotational slides frequently involve the above-mentioned regions. The
landslides usually present slow movements affecting areas with very variable extensions
(volumes ranging up to a few thousand cubic metres). Heavy rainfalls, geological complexity and
high seismicity usually are the triggering causes and dormant/suspended movements are
periodically reactivated during long rainy periods. Moderate to strong earthquakes are generally
accompanied by coseismic geological phenomena ranging from surface faulting to ground
cracks, landslides, liquefaction/compaction, which leave a permanent mark in the landscape. A
recent study established that in the Apennines Chain a minimum threshold of intensity for
landsliding is V MCS/MSK with distances up to 100 km from seismogenetic faults (Porfido et al.,
2002). Many complex movements have detachment surfaces unlikely detectable because in time
they deeply migrate when new materials are involved in the failures. Inclinometric measurements
often highlight this occurrence especially when clayey strata or tectonically deformed clayey
shale (“scaly varicoloured clays”) are involved. Consequently, it’s very difficult to design suitable
remedial works and correction of existing movements along roads because there is the doubt
that retaining structure foundations do not rest beyond the slide base. In Cilento area, the River
Rapi landslide, it is a sample problem for these design perplexities (De Riso and Santo, 1997). In
spite of many remedial works being carried out, a slow earth flow affects a wide area of Corleto
Monforte village and the provincial road (Fig. 11).
Figure 11. Geomorphological map of the T. Rapi landslide. 1) Detritical talus; 2)miocenic
flysch; 3) “Unità Sifilide” deposits; 4) mesozoic limestones; 5) fault; 6) borehole; 7) active
landslide; 8) dormant landslide; 9) crown of the relict landslide; 10) rotational slide; 11) flow;
12) trace of profile. (By De Riso & Santo, 1996)
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The earth flow developing from initial rotational slide affects a wide slope about 500 m in length
and the landslide debris (about 200.000 m3) shows a great quantity of counterslopes where the
displaced materials tilt back-ward toward the scarp.
It’s interesting to note that where arenaceous-marly or calcareous-clayey flysch are present often
the resistance of the heterogeneous rock masses is conditioned by the values of the residual
frictional angle of the clayey interbeds along which the movement occurs, their resistance values
being very low compared with the general resistance and deformability characteristics of the
entire formation (Fig.
12). Other factors having a marked influence on the large-scale behaviour of the Campanian
flysch with respect to roads are swelling and decompression, occuring as a result of excavations
(Cotecchia et al. 1992). Such phenomena have been observed along the faces of cuttings and in
deep trenches dug during the course of the numerous road constructions.
Figure 12. High River Ofanto valley: deep creep
movement overimposed on and old landslide body
(lioni Landslide) (By Cotecchia et al, 1992).
Lastly, many areas of the inner part of Campania (River Miscano, Tammaro, Ofanto and
Mingardo basins) are affected by small but very numerous slides involving villages and roads
(Fig.13) in a context already highly penalized from the socio-economic point of view (Budetta et
al, 1979; 1986; 1990).
11
Géoline 2005 – Lyon, France – 23rd - 25th, May/Mai 2005
Figure 13. Geolithologic map of Miscano basin. 1) Detritical talus; 2) alluvial deposits (a);
lacustrine deposits (b); 3) eluvial deposits; 4) pliocenic sand (a); clay (b); 5) miocenic chalk;
6) miocenic sandstone and conglomerate; 7) miocenic calcareous clay complex; 8)
calcareous-clay and silicoclastic complex; 9) “Unità Sicilide” clay deposits; 10) recent
landslide (a), ancient (b), area with recent large instability (c), ancient (d); 11) alluvial terrace.
(by Budetta et al, 1986).
Conclusions
Owing to rough relief, geological complexity and seismicity of regional territory, the Campanian
road system is exposed to very high landslide hazard and risk. According to the A.V.I. catalogue,
the landslides caused 61 casualties and about 100 injured road-users during the period between
1950 and 2001. The landslide density is very variable; some roads show landslide densities up to
about 0,9 landslides per kilometre; a mean value is about 0,3 landslides per kilometre. Rock-falls
and debris flows are the most frequent phenomena affecting cuts and steep slopes encumbering
roads in the north-western regional territory. Usually, these landslides involve small-sized
masses but are therefore very rapid and cause injury and death to the users of the said routes.
Slides, slow earth flows and complex landslides involving big volumes affect more gentle slopes
in the inner part of the region. These movements are less dangerous for motorists. Along with
kinematics factors characterizing potential instabilities (velocity, mass and run-out parameters),
also traffic density and available decision sight distance greatly affect the risk along roads.
Acknowledgements This work was carried out with financial contributions from the MURST ex
40%-60% under Prof. R. De Riso.
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