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Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
481
DOI: 10.4408/IJEGE.2013-06.B-46
GEOMATICS FOR SLOPE STABILITY AND ROCK FALL RUNOUT ANALYSIS:
A CASE STUDY ALONG THE ALTA TAMBURA ROAD
IN THE APUAN ALPS (TUSCANY, ITALY)
R
iccaRdo
SALVINI & M
iRko
FRANCIONI
University of Siena - Department of Environment, Earth and Physical Sciences and Centre of Geotechnologies - Siena, Italy
K
ey
words
: rock topple, runout, photogrammetry, laser scan-
ning, GIS
INTRODUCTION
The present research started in 2007 when, after a
rock fall event occurred during the night of February
27-28 in the Guadine village area (Fig. 1), the Massa
Municipality decided to conduct a detailed study on
the stability of the slope overhanging the Alta Tambura
road. The road connects Massa to five villages of the
Apuan Alps - Guadine, Gronda, Redicesi, Casania and
Resceto, which were isolated for several days because
of the main street destruction due to the event. The
presence of large angular boulders at the bottom of the
valley implies that this area has already experienced
ABSTRACT
With increasing awareness of geological risks, the
study of rocky slopes plays a key role in the Earth Sci-
ences, especially in areas of high vulnerability due to the
presence of human settlement. The present paper de-
scribes the stability and runout analyses carried out along
the Alta Tambura road, in correspondence with the Gua-
dine village connecting the Massa urban settlement to
the Apuan Alps (Tuscany, Italy). The integration among
various types of survey and analytical methodologies al-
lowed for the application of up-to-date approaches for
hazard assessment. Results from these types of studies
are useful in the decision-making process concerning
choosing the most appropriate mitigation works and, as
in such a case, their a posteriori validation. With regard
to the survey techniques, terrestrial laser scanning and
digital close-range photogrammetry were used to pro-
duce the digital elevation model, oriented stereo-images,
orthophotos and accurate positions and volumes of rocky
wedges and joints located on the slope overhanging the
analyzed road. Thanks to this data, a deterministic sta-
bility analysis was conducted and the spatial distribution
of rock fall density, velocities and kinetic energies was
modeled by means of the “cone-method”. Historical evi-
dence of rock falls, identified during fieldwork activities
and photointerpretation, were used to assess and cali-
brate the accuracy of results obtained from the method
and allowed, through a further 2D rock fall runout analy-
sis, the calculation of the dissipation energy that protec-
tion measures need to mitigate the risk in the area.
Fig. 1 - Orthophoto of the Guadine village showing the
zone affected by rock fall in 2007, and highlight-
ing Alta Tambura road on March 7, 2007; inset
map of Tuscany showing the Apuan Alps in red
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R. SALVIN1 & M. FRANCIONI
482
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
alii, 2005) we assessed the probabilistic distribution of
rock fall end points, velocity and kinetic energy along
the rock falling paths and existing barriers. By model-
ling the spatial distribution of rock fall frequency, we
improved the accuracy of the study moving from a 2D
analysis, which assumes that the fall follows the path
of steepest descent, to a 2.5D approach.
GEOLOGICAL AND GEOMORPHOLOGI-
CAL SETTING
In the rock fall area and at the base of the Renara
stream, outcrops are composed of lithotypes belonging
to the Paleozoic Crystalline Basement of the Apuan
“Autochthonous” (c
aRMignani
, 1985) which consists
of the “Porphyroids and porphiric schists” and the
“Lower Phyllites” formations. Porfiroids are made of
rhyolitic-rhyodacitic metavulcanites, are either light
green or gray in colour, with millimeter crystals of
quartz and feldspars in a quartzitic, muscovitic and
chloritic matrix. Porphiric schists are characterized
by muscovitic-chloritic fillads and metarkoses with
abundant quartzitic porphyroclasts., The “Grezzoni”
formation crops out on the slope, above the crystal-
line basement. Thin and discontinuous lenses of “Ser-
avezza Breccias” and “Megalodon marble” separate
this formation from the overlying “Dolomitic marble”,
which is made of light gray-pinky dolomite alternat-
ing with dolomitic marble. Such a geological sequence
belongs to the “Autochthonous” Unit and crops out in
the overturned limb of the “Vinca-Forno” anticline, a
non-cylindrical isoclinal NE-vergent fold, formed dur-
ing the first compressive deformation event (D1 phase)
and dated as late Oligocene - very early Miocene
(c
aRMignani
& k
ligfield
, 1990). Since the early Mi-
ocene, a second deformation phase (D2) overprinted
the earlier structures, generating new ductile to ductile-
brittle (and later only brittle) structures linked to post-
compression tectonic uplift and internal extension of
the piled-up tectonic units. In the study area, the folds
generated during the D2 phase show axes oriented at
N300° and dips gently towards the NE
With regard to the geomorphology, the study area
is strongly influenced by the structural-geological ar-
rangement of the Apuan Alps. The area belongs to the
M. Cipolla - M. Girello ridge characterized by a SW-
NE direction and by a very sharp crest, which varies
in elevation between 630 and 930 m a.s.l.. The upper
part of the ridge is composed of carbonaceous rocks
rock falls, leading to serious problems for the road.
The aim of this study is to acquire detailed geo-
logical and topographical information which, together
with climate and chemical weathering, induce rock
fracturing, opening of joints, rainfall infiltration, and
subsequent instability (l
iM
et alii, 2004). Once the
failure process initiates, the rock detaches and the fall-
ing trajectory is dictated by slope geometry and land
use. The lack of detailed data on slope topography, in-
stability source areas, rock block geometry and falling
paths, including runout distance, can limit the assess-
ment of rock fall hazard (d
oRRen
, 2003, g
lenn
et alii,
2006). In order to obtain all the information necessary
to perform the slope stability analysis and the rock fall
runout simulation, several types of geomatic surveys
and analytical methodologies were proposed. In this
paper, we used Digital Terrestrial Photogrammetry
(DTP) and Terrestrial Laser Scanning (TLS) to study
the geometric characteristics of slopes, rocky wedges
and discontinuities, thus overcoming problems like
the inaccessibility of outcrops and the complexity of
the slope morphology. Today, TLS is one of the best
ways to characterize the rock mass (f
ekete
et alii,
2010; t
aMbuRi
, 2008; n
guyen
et alii, 2011; R
unqiu
& X
iujun
, 2008), to analyze the slope stability (a
RM
-
esto
et alii., 2009; n
agalli
et alii, 2012; k
aspeR
-
ski
et alii, 2010), and to model the rock fall (a
bel
-
lán
et alii, 2010; O
ppikofeR
et alii, 2009; M
onnet
et alii, 2010). DTP also provides information about
the structural and geo-engineering setting of slopes.
Since the 1970s, photogrammetry has been utilized
to characterize the rocky mass (W
ickens
& b
aRton
,
1971; M
osaad
a
llaM
, 1978) and nowadays, thanks
to the advance of digital and informatic methodolo-
gies, it has became widespread either with (f
eRReRo
et alii, 2009; s
tuRzeneggeR
& s
tead
, 2009; S
alvini
et alii, 2011; s
alvini
et alii, 2013) or without TLS
(H
anebeRg
, 2008; R
oncella
et alii, 2005; S
tuRzeneg
-
ge
r et alii, 2009; f
iRpo
et alii, 2011).
The geomatics technologies used can yield ori-
ented stereo-images, orthophotos and precise digital
models of slopes and rocky wedges. Geometrical and
structural characteristics of slopes, such as joint atti-
tude, spacing and persistence, and block volumes, can
be also derived. The results were used together with
a deterministic method to evaluate the slope stability.
Through the application of the “cone-method” (t
oppe
,
1987; j
aboyedoff
& l
abiouse
, 2003, j
aboyedoff
et
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GEOMATICS FOR SLOPE STABILITY AND ROCK FALL RUNOUT ANALYSIS:
A CASE STUDY ALONG THE ALTA TAMBURA ROAD IN THE APUAN ALPS (TUSCANY, ITALY)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
483
trated rainfall events, alternated by dry periods. Stud-
ies carried out for the rock fall immediately following
the event occurred on February 27-28 (s
alvini
et alii,
2007a; s
alvini
et alii, 2007b) and additional in-depth
analyses performed by the Massa Municipality resulted
in the installation of several protectionary measures
(Fig. 2) such as beams, bars and inelastic and elastic
barriers both in the upper and lower part of the slope.
Elastic barriers, installed in 2010, are certified (E2000),
4 meters high and able to support up to 2,000 kJ
MATERIALS AND METHODS
With the aim of understanding the geological set-
ting of the slope and the consequent rock fall causes,
a new geological map with instability landforms at a
scale of 1:5,000 was produced (Fig. 3) based on field-
work surveys, existing literature (c
aRMignani
, 1985;
c
aRMignani
& k
ligfield
, 1990; d
i
p
isa
et alii, 1985)
and the official map of the Tuscany Region at a scale
of 1:10,000 (249110 section).
Moreover, engineering-geological surveys were
carried out in such a way as to have a complete under-
standing of the joint systems necessary to perform the
stability analysis of latent blocks. In addition to tradi-
tional geological, geomorphological and engineering–
geological surveys, DTP and TLS were used to carry
out a detailed analysis of discontinuities and wedges
throughout the slope, particularly in inaccessible ar-
eas. The photogrammetric survey was executed using
a reamed bar mounted on a topographic tripod set on
the slope facing the one under study. The distance be-
tween the zone of data acquisition and the slope was
ca. 300 m, thus requiring two digital cameras, Canon
TM
with a high slope gradient, and the intermediate and
lower parts of the slope consist of rocks belonging to
the crystalline basement with a lower slope gradient.
In addition to the slope gradient, type and presence of
the vegetation also influences the structural-geological
arrangement of the area; in fact, it was observed that
slopes appear rockier with the discontinuous vegeta-
tion in the highest part of the ridge, while dense forest
and soil cover is more prevalent in the lower part of the
slope. This type of morphology is quite common in the
Apuan Alps, as documented by literature with studies
on the influence of the geological-geomorphological
setting on landslides (b
aRoni
et alii, 2010; d’a
Mato
a
vanzi
et alii, 2000).
The rock fall occurred on the lower part of the
ridge, with the slope having a mean dip of approxi-
mately 38° and a rectilinear-convex profile, which,
according to l
eHMan
(1756), can be classified as a
“rectified slope”. The outcropping rocks in this area
experience strong physical weathering dominantly
caused by intense rainfall events. In fact, the meteoric
affluxes are very heavy in the Apuan Alps, with a mean
annual rainfall of over 3,000 mm (d’a
Mato
a
vanzi
et
alii, 2004). This pluvio-metric regime is controlled by
the particular climate of the Apuan Alps, referred to
as the Apennine–Mediterranean type, with transition
to the sub-coastal type, characterized by dry summers
and cold winters, with a primary peak of rainfall in the
autumn and two secondary maximums in the winter
and spring. This extreme climate feature is related to
the location and the shape of the Apuan Alps, which
intercept air flow originating from the Atlantic to the
west or the Mediterranean, and produce the forced lift-
ing of humid air masses, favoring their rapid adiabatic
cooling (d’a
Mato
a
vanzi
et alii, 2004). The physical
weathering acting in the area, together with karst phe-
nomena associated with the geology, are conducive to
slope instability, thus generating rock falls and debris
deposits accumulation in the morphological depres-
sions. Along the SE slope of the ridge, several nivation
niches host debris deposits that occasionally fail, while
the NW slope shows nivation hollows referable to the
last Pleistocene glaciation (b
ini
, 2005; f
edeRici
, 2005).
The Guadine event was interpreted as an effect
of physical weathering of porphyroids and porphiric
schists through surface processes, generating rock falls
on the steepest slopes. The rock debris deposits are at the
limit of equilibrium and can be mobilized after concen-
Fig. 2 - Examples of protectionary measures executed by
the Massa Municipality
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R. SALVIN1 & M. FRANCIONI
484
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
tion and two Leica
TM
System 1200 GPS receivers were
used for the topographic survey (Fig. 4A). Through the
GSM connection to the Leica Geosystems
TM
Spider-
Net network, differential GPS techniques were applied
with the aim of determining the absolute coordinates of
the system origin, and that of the azimuth zero direc-
tion. By this technique, since the total station allowed
for determination of the relative coordinates of sur-
veyed points (X, Y and Z) through the measurement
of angles and distances and trigonometric calculations,
absolute coordinates of ca. 100 GCP were calculated
and used for the absolute orientation of the images
within LPS module of ERDAS
TM
IMAGINE software.
Moreover, a Riegel
TM
Z420i TLS (Fig. 4B) was
used to acquire a point cloud necessary for the 3D
modelling of the slope. The distance between the slope
and the instrument ranged from 250 to 400 m and the
spatial resolution of the point cloud was set to 7 cm at
a distance of 300 m, corresponding to a scanning angle
of 0.013°. The point cloud was stored and processed
using Leica
TM
Cyclone software. The described topo-
graphic survey was also utilized for the registration to
absolute coordinates of the TLS point cloud.
Data was analyzed by DTP and 3D modelling
techniques that, managed within a Geographical In-
formation System (GIS), constructed a complete
deterministic understanding of the geometric charac-
Eos5D and Eos20D, with focal lengths varying from
10 to 200 mm to produce detailed and panoramic pho-
tos. The resolution of the two cameras was set to 14
and 8 Megapixel, respectively. The direction of strips
was oriented parallel to the slope as much as possible,
at N65, with pitching at approximately ±15° from the
horizontal in order to have a complete photographic
coverage of the unstable slope.
Differential GPS and topographic surveys were
also carried out in order to collect Ground Control
Points (GCP), that were clearly visible on the slope and
necessary for the absolute orientation of the images. A
Leica
TM
TCRP 1203+R1000 (reflectorless) total sta-
Fig. 4 - Topographic surveying with the total station (A);
TLS during data acquisition (B)
Fig. 3 - Geological map showing instability landforms and a cross section; (black-colored fold axes represent minor struc-
tures of D1 phase within the “Vinca-Forno” anticline; blue-colored structures relate to antiform and synform axes of
the D2 phase refolding of the primary schistosity)
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GEOMATICS FOR SLOPE STABILITY AND ROCK FALL RUNOUT ANALYSIS:
A CASE STUDY ALONG THE ALTA TAMBURA ROAD IN THE APUAN ALPS (TUSCANY, ITALY)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
485
0.049 for the horizontal and vertical acceleration, re-
spectively. The percentage of water saturation in joints
was empirically varied from 0 to 100%. The procedure
was carried out in accordance to the Italian Norme Tec-
niche per le Costruzioni (NTC) (M.LL.PP., 2008). In
addition to the deterministic study, a probabilistic and
sensitivity analysis on Safety Factor (SF) related to the
critical joint system was performed with the aim of de-
fining its variation as combination of input variables,
as shown in Tab. 1.
Taking into account the presence of the road and
the houses at the bottom of the slope, results of the sta-
bility study were integrated with a detailed rock fall ru-
nout analysis based on the DEM. The analysis was con-
ducted by means of RocFall software (Rocscience
TM
).
The “cone-method” was applied through the free-
ware Conefall software (Quanterra
TM
) in order to cal-
culate the spatial distribution of rock fall transit den-
sity, velocities and kinetic energy. This required the
usage of the DEM and the source position of the most
dangerous blocks sited on the slope, which were iden-
tified through the photointerpretation of terrestrial pho-
tos. Results were used to validate the dispersion areas
and to create proper rock fall trajectories. This method
maps the general rock fall spatial distribution and is
helpful in understanding which areas could be affected
by a hypothetic rock fall. However, values obtained
from these simulated rock fall events were calculated
based on all the blocks sited on the slope in this study,
so the real velocity and kinetic energy which could
be reached during a fall could not be determined for
each individual block. Hence, with the aim of trying to
overcome such a limitation, the method was calibrated
by calculating the volume of rocky blocks present at
the bottom of the valley, which are remnants of past
failures from the slope. This was conducted using
fieldwork data and evidence from photointerpretation.
This, in combination with a further 2D rock fall simu-
lation, allowed us to better assess the kinetic energy of
blocks during the fall and, consequently, the dissipa-
tion energy that protection measures should have in or-
der to effectively mitigate the risk of similar collapses.
RESULTS
The cognitive survey shows that the 2007 rock
fall originated from an elevation of 316 m a.s.l.,
forming a detachment niche 18 m wide. The rock fall
reached the Renara stream bed at an elevation of 180
teristics of slopes, wedges and joints. These, together
with engineering-geological fieldwork measurements,
allowed for the analysis of the stability of the slope and
the rock fall runout.
Kinematic analyses of stability were carried out
using joint systems so that latent phenomena could
be geometrically identified. Dips. 6.0 software (Roc-
science
TM
) was used for this deterministic study, using
friction angles from the engineering-geological survey
and several slope attitudes as computed from spatial
processing of the Digital Elevation Model (DEM). The
DEM was created from TLS data which was merged
to morphological features, which were stereo-restituted
from terrestrial and aerial photographs, and altogether
were merged to the existing topographic maps at a
scale of 1:2,000; this activity was necessary to fill shad-
ows that resulted in the point cloud in proximity to veg-
etated areas and at the toe of the slope near the stream
bed. The final DEM was created in grid format with a 1
m cell size. Spatial analysis techniques were applied to
the DEM in order to obtain the slope and the aspect of
different slope zones, giving the dip and dip direction
to be utilized in the stability analysis. Spatial variability
of the slope morphology was then used for the purpose
of studying the steadiness of several dipping slopes, up
to the computed maximum stable slope angles.
Results from the kinematic stability analysis high-
lighted a critical joint system conducive to toppling.
Hence, we performed a dynamic study using the beta
testing version of the RocTopple software (Rocscien-
ce
TM
), which is based on the g
oodMan
& b
Ray
method
(1976). The study was carried out under both static and
dynamic conditions, dependant on the local seismic ac-
celeration and the percentage of water saturation. We
derived seismic coefficients (dimensionless numbers
that define the seismic acceleration as a fraction of the
acceleration due to gravity) from the GeoStru PS soft-
ware (g
eo
s
tRu
, 2008), obtaining values of 0.099 and
T
ab. 1 - Variables and relative ranges used in the probabi-
listic study on SF
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R. SALVIN1 & M. FRANCIONI
486
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
m a.s.l., overtopping a 90 m long stretch of the Alta
Tambura road.
The study revealed that the landslide originated
as a rock topple involving boulders and soil in prox-
imity to an hold trail which was characterized, in that
part, by a dry stone wall. Rainfall events in the days
preceding the landslide led to initial failure triggered
by poor drainage and an increase of water pressure
at the interface between debris and rocky basement.
Toppling of rock down the steep slope by bouncing,
rolling and sliding then increased the volume of the
failed mass, clearing the slope of soil, debris and
stones in unstable equilibrium and destroying the
old anthropic terraces which characterized the slope
from 250 to 185 m a.s.l.. The mechanism which
caused such an event represents one of the most
critical geomorphologic vulnerabilities of the zone,
prone to rock toppling and to the difficulties of con-
trolling the water runoff.
The integration of geomatics and traditional en-
gineering-geological surveys allowed for the deter-
mination of the attitude of joint systems and slopes.
Measurements from DTP were compared with field-
work data by means of a density analysis of attitudes
in stereographic projection (Fig. 5). As shown in the
figure, similarities between the joint distribution ob-
tained through engineering-geological surveys and
DTP are evident, even if the photogrammetric data
have a greater dispersion. This is because the engi-
neering-geological survey was carried out in acces-
sible outcrops, whereas DTP photointerpreted joints
refer to the whole 3 ha wide slope. The larger the area
under study, the more the attitude of joints may vary.
Nevertheless, the mean attitude derived from the two
methods corresponds well with data variability that is
always less than 10° (Tab. 2).
T
ab. 2 - Mean values of joint systems attitude from geo-
engineering survey and DTP
Fig. 5 - Contour plots of joint systems from engineering-geological survey and DTP. Data is presented using stereographic
projection through the Schmidt equal-area method
Tab. 3 - Variation of SF in different slopes taking into ac-
count water saturation in joints and local seismic
acceleration (sc=seismic coefficients)
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GEOMATICS FOR SLOPE STABILITY AND ROCK FALL RUNOUT ANALYSIS:
A CASE STUDY ALONG THE ALTA TAMBURA ROAD IN THE APUAN ALPS (TUSCANY, ITALY)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
487
points for failures and for the measurement of the
volume of the most dangerous blocks located on
the slope, yielding sizes ranging from 7 to 500 m
3
and a mean value of 90 m
3
. This was followed by a
dynamic stability analysis of the F2 system, which
included the computation of the slope stability limit
angles. In addition to the geometrical characteristics
of slopes and joints, RocTopple also requires input
data such as the rock unit weight (2.7 t/m
3
), the shear
strength model (Mohr-Coulomb), the joints friction
angle (30°) and the cohesion (0.04 t/m
2
). The values
used for this computation came from the engineer-
ing-geological survey, rock mass classification and
literature. Table 3 shows the variation of SF for dif-
ferent slopes up to the slope stability limit angles,
taking into account water saturation in joints and lo-
cal seismic acceleration. It shows that SF is always
greater than the physical limit (1.00) with the excep-
tion of slope stability limit angles which lie close to
or below 1.00, both in static and dynamic conditions.
The change of slope dip direction and the relative
F2 apparent dip reduction cause the decrease of SF.
Based on slope morphology as measured from the
DEM, the kinematic stability analysis was conducted
by testing several slopes with dip directions and dips
varying respectively from 115 to 160° and from 40 to
60°. The F2 joint system proved positive to toppling
failures and the subsequent kinematic analysis, aimed
to calculate the slope stability limit angles, gave the
following results: if considering 30° of dip direction
variability plus a tolerance of 10° because of system
scattering, unstable slopes may vary from 125 to 205°
in dip direction with a dip of about 13°. When dealing
with toppling kinematic analyses, the friction angle
(30° for the F2 system) must also be considered to
compute the slope limit angle, so that it may finally
vary from 125/43 to 205/43.
By means of spatial analysis techniques, these
values of dip direction and dip were applied within
ArcGIS software (ESRI
TM
) to map the combination
between “aspect” and “slope” calculated from the
DEM; this processing made it possible to highlight
areas potentially prone to this kind of collapse (Fig. 6)
DTP allowed for the identification of the source
Fig. 6 - Map of source points and areas where the slope attitude values are out of the stability range for F2 joint system
toppling (A). Stereographic projection of maximum stable slope angles using the Wulff equal-angle method (B)
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R. SALVIN1 & M. FRANCIONI
488
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
the method in terms of rock fall velocity and kinetic
energy, all the achieved results were then confirmed
through comparison with evidence of rocky blocks
collapsed in the past from the slope and recognizable
today on the stream bed.
Thus, considering the position and the typology
of the barriers installed on and at the foot of the slope,
a further 2D runout analysis was carried out with the
aim of evaluating the kinetic energy that every sin-
gle block could potentially have upon impact with the
protectionary structures. Fig. 9 shows an example of
such an analysis where a block, during ten trials, is
successfully stopped by the barriers. Knowing this
deterministic energy, it was possible to verify the ef-
ficiency of the installed protectionary measures in any
different studied zones. Results of this study showed
very high values of kinetic energy when simulating
the detachment of big blocks located at the top of
the slope. The value of impacting energy decreased
for smaller blocks or those sited in the lower part of
the slope. It is important to underline that the Massa
Municipality installed protection barriers which are
either double or triple-lined. Therefore, acting togeth-
er, these barriers could limit even very high rock fall
energy (Fig. 9). Considering that the value of kinetic
energy was sometimes much larger than one toler-
able by the most efficient existing passive protection
systems, additional active reinforcements have been
adopted and partially completed. This has been pos-
sible through the installation of steel cable panels, the
attachment of blocks to stable portions of the slope
The cumulative plots of Fig. 7 show results of
the probabilistic sensitivity analysis of failure. The
stability of the actual slope (plot A in Fig. 7) is par-
ticularly influenced by water saturation in joints and
slope angle, confirming the need for proper water
management and morphological and land use main-
tenance. As expected, the stability of the slope limit
angles (plot B in Fig. 7 showing the case of the slope
oriented at 125/43) is hardly affected by the variabil-
ity of its dip value and secondly by water saturation
in joints and joint friction angle.
The final step of the study was the rock fall runout
analysis, which was aimed firstly, at verifying the prob-
ability of blocks which were identified of reaching the
road and houses and secondly, at establishing the worth
of measures of protection necessary to manage the risk.
The analysis showed that a wide area located at the bot-
tom of the studied slope could be intensively affected
by block fall. Maps of Fig. 8 show: i) the source points
of potential rock fall events (Fig. 8A) corresponding to
unstable blocks, as defined during the photogrammetric
and the stability analyses; ii) the rock fall transit density
(Fig. 8B), the rock fall velocity (Fig. 8C) and the rock
fall kinetic energy (Fig. 8D).
It is important to emphasize that results do not
come only from a 2D runout simulation, which is lim-
ited to creating rock fall profiles subjectively and lacks
modeling of the lateral trajectory dispersion, but from
a combination with the “cone-method” which analy-
ses the spatial frequency (j
aboyedoff
et alii, 2005).
Moreover, as already mentioned, in order to calibrate
Fig. 7 - Cumulative plots of input variables in the sensitivity analysis of failure; the actual slope 160/40 (A) and the
slope stability limit angle 125/43 (B)
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GEOMATICS FOR SLOPE STABILITY AND ROCK FALL RUNOUT ANALYSIS:
A CASE STUDY ALONG THE ALTA TAMBURA ROAD IN THE APUAN ALPS (TUSCANY, ITALY)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
489
Fig. 8 - Source points of rock fall (A); map of rock fall transit density (B); map of rock fall velocity (C); map of rock fall
kinetic energy (D)
Fig. 9 - Example of a 2D rock fall runout simulation before (A) and after the installation of the protective barriers (B)
background image
R. SALVIN1 & M. FRANCIONI
490
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
through bars, bolts and steel cables and slings, and the
creation of more efficient draining systems necessary
to avoid water overpressures.
CONCLUSIONS
Geological and engineering-geological studies, in-
tegrated with geomatics surveys, highlight the intercon-
nection between geological setting, geomorphology,
meteorological events, climate and slope instability.
Under particular climatic conditions and land conser-
vation abandonment, rock blocks and debris deposits
could trigger unexpected failures which are then able to
evolve into large landslides, as in this case study.
Moreover, this study demonstrated that by inter-
acting with other systems and the slope, the F2 joint
system could generate rock blocks prone to toppling,
as proven by the presence of large angular boulders at
the bottom of the valley.
The attitude of other joint systems, variously dip-
ping towards the slope (i.e. F1, K2), favors water in-
filtration and, without the creation of more efficient
drainage networks, could induce new instability events.
The estimation of the area affected by rock fall
was produced through the analysis of the transit den-
sity spatial distribution. Based on these results, the
subsequent 2D runout analysis enabled calculation
of the proper trajectories and determination of the en-
ergy that blocks could reach during hypothetical slope
rockfall. Knowing the kinetic energy of blocks made
it possible to evaluate and assess the efficiency of pro-
tectionary systems which have been installed.
ACKNOWLEDGMENTS
The authors wish to acknowledge the support by
Massa Municipality, geol. Andrea Piccinini and Roc-
science Inc.
REFERENCES
a
bellan
a., c
alvet
j., v
ilaplana
j.M. & b
lancHaRd
j. (2010) - Detection and spatial prediction of rockfalls by means of
terrestrial laser scanner monitoring. Geomorphology, 119: 162-171.
a
RMesto
j., o
Rdonez
c., a
lejano
l. & a
Rias
p. (2009) - Terrestrial laser scanning used to determine the geometry of a granite
boulder for stability analysis purposes. Geomorphology, 106: 271-277.
b
aRoni
c., R
ibolini
a., b
RuscHi
g. & M
annucci
p. (2010) - Geomorphological map and raised-relief model of the Carrara
marble Basins, Tuscany, Italy. Geogr. Fis. Dinam. Quat., 33: 233-243.
b
ini
M. (2005) - Glacial landforms in the Apuan Alps (Tuscany -Italy): features in danger of extinction. Il Quaternario, Italian
Journal of Quaternary Sciences, 18 (1): 175-178.
c
aRMignani
L. & k
ligfield
R. (1990) - Crustal extension in the Northern Apennines: the transition from compression to
extension in the Alpi Apuane core complex. Tectonics, 9: 1275-1303.
c
aRMignani
L. (1985) - Carta geologico-strutturale del complesso metamorfico delle Alpi Apuane (Foglio Nord) - Scala
1:25.000. LAC - Litografia Artistica Cartografica, Florence, Italy.
d'a
Mato
a
vanzi
g., g
ianneccHini
g. & p
uccinelli
R. (2000) - Geologic and geomorphic factors of the landslides triggered
in the Cardoso T. Basin (Tuscany, Italy) by the June 19, 1996 intense rainstorm. Proc. of 8
th
International Symposium on
Landslides: 381-386.
d'a
Mato
a
vanzi
g., g
ianneccHini
g. & p
uccinelli
R. (2004) - The influence of the geological and geomorphological settings
on shallow landslides. An example in a temperate climate environment: the June 19, 1996 event in northwestern Tuscany
(Italy).
Engineering Geology, 73: 215-228.
d
i
p
isa
a., g
attiglio
M., M
eccHeRi
M. & v
ietti
n. (1985) - Nuovi dati sulle Metabasiti della Valle del Giardino del Basamento
Paleozoico Aprano. Atti Soc. Tosc. Sc. Nat. Ser.A, 95: 89-103.
d
oRRen
L.K.A. (2003) - A review of rock fall mechanics and modelling approaches. Progress in Physical Geography, 27: 69-87.
f
edeRici
P.R. (2005) - Aspetti e problemi della glaciazione Pleistocenica nelle Alpi Apuane. Istituto Italiano di Speleologia.
Memorie, Ser.II, 18: 19-32.
f
ekete
s., d
iedeRicHs
M. & l
ato
M. (2010) - Geotechnical and operational applications for 3-dimen. laser scanning in drill and
blast tunnels. Tunnelling and Underground Space Technology, 25: 614-628.
f
eRReRo
a.M., f
oRlani
g., R
ondella
R. & v
oyat
H.i. (2009) - Advanced geostructural survey methods applied to rock mass
characterization. Rock Mechanics and Rock Engineering, 42 (4): 631-665.
f
iRpo
g., s
alvini
R., f
Rancioni
M. & R
anjitH
p.g. (2011) - Use of digital terrestrial photogrammetry in rocky slope stability
background image
GEOMATICS FOR SLOPE STABILITY AND ROCK FALL RUNOUT ANALYSIS:
A CASE STUDY ALONG THE ALTA TAMBURA ROAD IN THE APUAN ALPS (TUSCANY, ITALY)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
491
analysis by distinct elements numerical methods. International Journal of Rock Mechanics and Mining, 48 (7): 1045-1054.
g
eo
s
tRu
(2008) - GeoStru PS Software. http://www.geostru.com/geoapp/parametrisismici.aspx (access date 18 February, 2013).
g
lenn
n.f., s
tReutkeR
d.R., c
HadWick
d.j., t
HackRay
g.d. & d
oRscH
S.J. (2006) - Analysis of LiDAR-derived topographic
information for characterizing and differentiating landslide morphology and activity. Geomorphology, 73: 131-148.
g
oodMan
R.e. & b
Ray
J.W. (1976) - Toppling of rock slopes. ASCE Specialty Conference on Rock Engineering for Foundations
and Slopes, 2: 201-234.
H
anebeRg
W.C. (2008) - Using close range terrestrial digital photogrammetry for 3-D rock slope modelling and discontinuity
mapping in the United States. Bulletin of Engineering Geology and the Environment, 67: 457-469.
j
aboyedoff
M., d
udt
J.P. & l
abiouse
V. (2005) - An attempt to refine rock fall hazard zoning based on the kinetic energy,
frequency and fragmentation degree. Nat Hazard Earth Sys, 5: 621-632.
j
aboyedoff
M. & l
abiouse
V. (2003) - Preliminary assessment of rockfall hazard based on GIS data. 10
th
International Congress
on Rock Mechanics ISRM 2003, Technology Roadmap for Rock Mechanics. South African Institute of Mining and
Metallurgy, Johannesburg, South Africa, 575-578.
k
aspeRski
j., d
elacouRt
c., a
lleMand
p., p
otHeRat
p., j
aud
M. & v
aRRel
E. (2010) - Application of a terrestrial laser scanner
(TLS) to the study of the Séchilienne Landslide (Isère, France). Remote Sens., 2: 2785-2802.
l
eHMann
J.G. (1756) - Versuch einer Geschichte von Flötz-Gebürgen betreffend deren Entstehung, Lage, darinne befindliche
Metallen, Mineralien und Foßilien größtentheils aus eigenen Wahrnehmungen und aus denen Grundsätzen der Natur-Lehre
hergeleitet, und mit nöthigen Kupfern versehen
. Berlin, Germany, 76 pp.
l
iM
c.H., d
eRek
M
aRtin
c. & H
eRd
e.p.k. (2004) - Rock fall hazard assessment along railways using GIS. (CD-ROM)
Proceedings of the 57
th
Canadian Geotechnical Conference. Quebec City, Canada, 1-8.
M.LL.PP. - M
inisteRo
dei
l
avoRi
p
ubblici
(2008) - NTC Norme Tecniche per le Costruzioni. D.M. del 14/01/2008. Gazzetta
Ufficiale della Repubblica Italiana, 04.02.2008, 15-25 (and pp. 196-198).
M
onnet
j.M., c
louet
n., b
ouRRieR
f. & b
eRgeR
f. (2010) - Using geomatics and airborne laser scanning for rock fall risk
zoning: a case study in the French Alps. Canadian Geomatics Conference and Symposium of Commission I (ISPRS).
Calgary, Alberta, Canada.
M
osaad
a
llaM
M. (1978) - The estimation of fractures and slope stability of rock faces using analytical photogrammetry.
Photogrammetria, 34 (3): 89-99.
n
agalli
a., f
ioRi
a.p., n
agalli
b. & d
os
s
antos
i
zzo
R.l. (2012) - Terrestrial laser scanning on rock mass stability analysis.
Electronic Journal of Geotechnical Engineering, 17/Bundle M, 1817-1831.
n
guyen
H.t., f
eRnandez
-s
teegeR
t.M., W
iatR
t., R
odRigues
d. & a
zzaM
R. (2011) - Use of terrestrial laser scanning for
engineering geological applications on volcanic rock slopes - an example from Madeira island (Portugal). Nat. Hazards
Earth Syst. Sci., 11: 807-817.
o
ppikofeR
t., j
aboyedoff
M., b
likRa
l., d
eRRon
M.H. & M
etzgeR
R. (2009) - Characterization and monitoring of the Aknes
rockslide using terrestrial laser scanning. Nat. Hazards Earth Syst. Sci., 9: 1003-1019.
R
oncella
R., f
oRlani
g. & R
eMondino
F. (2005) - Photogrammetry for geological applications: automatic retrieval of
discontinuity orientation in rock slopes. Proceedings of SPIE-IS&T Electronic Imaging, SPIE, 5665: 17-27.
R
unqiu
H. & X
iujun
d. (2008) - Application of three-dimensional laser scanning and surveying in geological investigation of
high rock slope. Journal of China University of Geosciences, 19: 184-190.
s
alvini
R., f
Rancioni
M., f
antozzi
p.l., R
iccucci
s., b
onciani
f. & M
ancini
s. (2011) - Stability analysis of “Grotta delle Felci”
Cliff (Capri Island, Italy): structural, engineering-geological, photogrammetric surveys and laser scanning. Bulletin of
Engineering Geology and the Environment, 70 (4): 549-557.
s
alvini
R., f
iRpo
g., c
aRMignani
l., f
antozzi
p.l., a
iello
e., c
oRniani
M., M
assa
g., b
onciani
f., l
apini
M. & c
occa
p.
(2007a) - Studio della frana di Guadine (MS) attraverso fotogrammetria digitale terrestre, laser scanner e rilievi geologici.
11° Conferenza Nazionale ASITA, Turin, Italy, November 6-9, II: 1937-1942.
s
alvini
R., f
iRpo
g., c
aRMignani
l., f
antozzi
p.l., a
iello
e., c
oRniani
M., M
assa
g., b
onciani
f., l
apini
M. & c
occa
p.
(2007b) - Study of the Guadine rockfall (Massa district, Italy) by digital terrestrial photogrammetry, laser scanner and
geological, geomorphological and geomechanical surveys.
Geoitalia 2007, VI Forum Italiano di Scienze della Terra,
Rimini, Italy, September 12-14, 2: 205.
background image
R. SALVIN1 & M. FRANCIONI
492
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
s
alvini
R., f
Rancioni
M., R
iccucci
s., b
onciani
f. & c
allegaRi
i. (2013) - Photogrammetry and laser scanning for analyzing
slope stability and rock fall runout along the Domodossola-Iselle railway, the Italian Alps. Geomorphology, 185: 110-122.
s
tuRzeneggeR
M., s
tead
d., b
eveRidge
a. & l
ee
S. (2009) - Long-range terrestrial digital photogrammetry for discontinuity
characterization at Palabora open-pit mine. In d
iedeRicHs
M. & g
Rasselli
g.
eds
. “ROCKENG09: Proceedings of the 3
rd
CANUS Rock Mechanics Symposium”, Toronto, paper 3984, 10 pp.
s
tuRzeneggeR
M. & s
tead
d. (2009) - Close-range terrestrial digital photogrammetry and terrestrial laser scanning for
discontinuity characterization on rock cuts. Engineering Geology, 106: 163-182.
t
aMbuRi
A. (2008) - The use of terrestrial laser scanner for the geomechanical characterization of inaccessible unstable rock
slopes. Workshop on “Landslide monitoring techniques based on remote sensing tools”, EC FP6 Galahad project, Madrid,
October 17, 2008.
t
oppe
R. (1987) - Terrain models - a tool for natural hazard mapping. Proceedings of the Davos Symposium. Avalanche
formation, movement and effects. IAHS Publication, 162: 629-638.
W
ickens
e.H. & b
aRton
n.R. (1971) - The application of photogrammetry to the stability of excavated rock slopes. The
Photogrammetric Record, 7 (37): 46-54.
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