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Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
123
DOI: 10.4408/IJEGE.2013-06.B-09
A PHYSICALLY-BASED SCALE APPROACH TO THE ANALYSIS OF
THE CREEP PROCESS INVOLVING MT. GRANIERI (SOUTHERN ITALY)
A
lberto
BRETSCHNEIDER
(*)
, r
inAldo
GENEVOIS
(**)
, S
AlvAtore
MARTINO
(***)
,
A
lberto
PRESTININZI
(***)
& G
iuSeppe
VERBENA
(****)1
(*)
French Institute of Science and Technology for Transport, Development and Networks (IFSTTAR) – Nantes, France
(**)
University of Padua - Department of Geosciences - Padua, Italy
(***)
Sapienza University of Rome - Department of Earth Sciences and CERI Research Centre - Rome, Italy
(****)
Tecnostudi Ambiente s.r.l. Professional Company - Rome, Italy
ascribe tertiary-creep deformations at Mt. Granieri to a
highly altered portion of granites and to an underlying
poorly altered one, and iii) demonstrate that deforma-
tions of the portion of the slope located a few hundreds
of metres from the valley floor were dependent on a
stationary (secondary-stage) creep process.
K
ey
word
: rock mass creep, physic-analogical modelling,
gravitational deformations
INTRODUCTION
Deep-seated gravitational slope deformations
(DSGSDs), associated with time-dependent rock
mass behaviours, are widely documented in the Ap-
ennine chain, where rigid and ductile materials hav-
ing a different rheological behaviour are juxtaposed
(n
emcok
& b
AliAk
, 1977; c
Anuti
et alii, 1990; c
onti
& t
oSAtti
, 1993; e
SpoSito
et alii, 2007; b
ozzAno
et
alii, 2008; b
ozzAno
et alii, 2013). The southern Ca-
labria Apennines have still active tectonic uplifts of
Pleistocene-Holocene age; in this sector, DSGSDs are
the result of both an intense morphological evolution,
due to subaerial erosion, and of geomechanical condi-
tions with slope-scale effects, e.g. advanced alteration
of rocks making up the local crystalline-metamorphic
bedrock. Numerous studies have stressed the role of
altered granitic rocks as a triggering factor for gravity-
induced slope deformations, which can evolve into
large landslides (G
enevoiS
& p
reStininzi
, 1979a; G
e
-
nevoiS
& p
reStininzi
, 1979b; p
reStininzi
, 1984; p
el
-
ABSTRACT
1
In January 1972, a rock slide of more than 2 million
m
3
moved along the north-eastern slope of Mt. Grani-
eri (900 m above sea level), in the Allaro River basin,
close to Salincriti village (Calabria region, southern
Italy). Subsequent field investigations (geomechanical
surveys and laboratory creep tests on rock samples )
validated the initially assumed ongoing “retrogressive”
evolution of the phenomenon, which is mobilising a
rock mass volume of about one million m
3
. Data from
a remote monitoring system (2 stationary inclinometers
at different depths + 1 piezometer) and topographic
surveys helped improve the understanding of these
slope instabilities. Collected data were used to test a
physically-based spatio-temporal approach permitting
to scale up laboratory creep test results to the deforma-
tional processes of natural slopes. The study assessed
whether a time-dependent phenomenon, already at a
tertiary-creep stage, was responsible for the deforma-
tional processes observed at Mt. Granieri, whose mor-
phological evidence was both reported in the literature
about its historical landslides and visible in the topmost
portions of the slope. Quantitative analysis of labora-
tory curves, scaled up to the natural process, made it
possible to: i) confine tertiary-creep deformations to
the topslope and to the first 300 m from the surface; ii)
1
Study carried on as part of the Research Project
PRIN 2010-2011 (funded by the Italian Ministry for Education,
University and Research), prot. 20102AXKAJ, Coordinator: A.
Prestininzi
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124
International Conference on Vajont - 1963-2013 - Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
River flows, of about 800 m (Fig. 2). The slope is made
up of crystalline lithotypes, forming a granitic intru-
sive complex (Permian-Carboniferous, b
onArdi
et alii,
1984) in its middle-lower portion and a metamorphic
one (Carboniferous?-Devonian-Silurian?) in its upper
part. Granites and granodiorites outcrop at an average
elevation of 215 to 700 m asl. The remaining 300 m
consist of: i) a metamorphic transitional belt, which
represents a contact zone, with a thickness of 20 to 50
m (heat-metamorphosed biotitic schists) and contact
metamorphism of medium-low grade, and ii) biotitic
schists, exposed in the topmost portions of the slope
(p
elleGrino
, 2000; b
ArreSe
et alii, 2006; p
elleGrino
& p
reStininzi
, 2006; p
elleGrino
et alii, 2008). The
heat-metamorphic contact and the overlying biotitic
schists accommodate pegmatitic and/or hydrothermal
intrusions, associated with sulphide mineralisations
(b
onArdi
et alii, 1982). Stratigraphic relations between
crystalline-metamorphic units are highly disturbed by
some NW-SE-trending tectonic lines having a domi-
nantly left-lateral strike-slip movement and a weak
extensional component (p
elleGrino
, 2000; p
elleGrino
et alii, 2008). All of the above crystalline-metamorphic
lithotypes have been experiencing diffuse and intense
physico-chemical alteration processes. The latter proc-
esses are concentrated along metamorphic-aureole
belts, as highlighted by multiple studies conducted in
the Mt. Granieri area (G
enevoiS
& p
reStininzi
, 1979a;
G
enevoiS
& p
reStininzi
, 1979b; p
reStininzi
, 1984; p
el
-
leGrino
, 2000; m
Artino
et alii, 2004; b
ArreSe
et alii
2006; p
elleGrino
& p
reStininzi
, 2006; p
elleGrino
et
alii, 2008; r
AmAn
Y.v & G
oGte
b.S., 1982). Four dif-
ferent stages of alteration were identified for the above
lithotypes. G
enevoiS
& p
reStininzi
(1979b) character-
ised the different states of alteration of the Mt. Granieri
leGrino
, 2000; m
Artino
et alii, 2004; b
ArreSe
et alii
2006; p
elleGrino
& p
reStininzi
, 2006; p
elleGrino
, et
alii, 2008). Understanding the processes governing the
evolution of slopes is crucial to investigating their sta-
bility and DSGSDs acting over a wide spatio-temporal
scale (m
Affei
et alii, 2005). These deformations are
generally supposed to obey time-dependent deforma-
tion laws and to undergo different evolutionary stages,
expressed by continuous creep-induced deformations.
A geological-evolutionary model of the slope, com-
bined with targeted studies (e.g. lab tests and model-
ling), may help gather quantitative data on geomor-
phology and stress-strain behaviour of the affected
materials (m
Affei
et alii, 2005).
The analysis described in this paper was carried
out on the Mt. Granieri slope (southern Calabria, It-
aly), which is involved in a large-scale deformational
process affecting considerable volumes of the Pal-
aeozoic crystalline-metamorphic bedrock. The main
objective of the study was to analyse and gain more
insight into the time-dependent behaviour of rock
masses and, under an experimental approach, to scale
up the results of creep tests carried out on specimens
from the investigated area to the overall slope. A phys-
ically-based spatio-temporal scale approach was thus
developed and applied to laboratory data, with a view
to determining the creep stages that the rock mass had
reached in different sectors of the slope.
GEOLOGICAL AND GEOMORPHOLOGI-
CAL FEATURES
Mt. Granieri is located on the Ionian side of the
Serre Calabresi massif, in the middle-upper portion of
the Allaro River basin (Figs 1 and 2 ), extending for
about 130 km
2
. The slope is roughly NW-SE-trending,
with elevations of up to 1,000 m above sea level (asl)
and a height from the valley floor, where the Allaro
Fig. 1 - a) location of the study area and b) north-eastern
slope of Mt. Granieri, where the area of detach-
ment of the 1972 landslide at the top of the slope
is visible
Fig. 2 - Upslope evolution of the large 1972 landslide,
with the position of the future scarp
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A PHYSICALLY-BASED SCALE APPROACH TO THE ANALYSIS OF THE CREEP PROCESS
INVOLVING MT. GRANIERI (SOUTHERN ITALY)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
125
PLIO-PLEISTOCENE EVOLUTION OF
THE MT. GRANIERI SLOPE
The evolutionary model of the north-eastern slope
of Mt. Granieri was reconstructed via geomorphologi-
cal analysis of different topographic sections transver-
sal to the Allaro River valley. Records of subhorizontal
flat surfaces, located at comparable elevations on the
slopes of both the left and right banks of the stream,
were interpreted as river strath terraces (sensu G
ArciA
,
2006). These terraces may have been built during dif-
ferent phases of standstill in the Allaro River erosional
activity. Given their topographic elevations, the Allaro
River strath terraces correlate with multiple orders of
marine terraces along the Ionian coast of Calabria and
on the Aspromonte massif (m
iYAuchi
et alii, 1994). In
more detail, the strath Allaro River terrace at an eleva-
tion of about 620 m asl correlates with the 3
rd
-order
marine terrace (estimated date: 1000 ka). The strath
Allaro River terrace at about 510 m asl correlates with
the 4
th
-order marine terrace (estimated date: 950 ka).
This surface may also correlate with the terrace un-
derlying the small town of Gerace (Calabria), about
20 km south of the investigated area, and consisting
of calcarenites, sandstones and sands supposedly be-
longing to the Mt. Narbone formation (b
ozzAno
et
alii, 2010). The strath Allaro River terrace at about
450 m asl correlates with the 5
th
-order marine terrace
(estimated date: 900 ka). The strath Allaro River ter-
race at about 380 m asl correlates with the 6th-order
marine terrace (estimated date: 400 ka). Finally, the
strath Allaro River terrace at about 300 m asl corre-
lates with the 7
th
-order marine terrace (estimated date:
300 ka). This surface can thus be correlated with the
Caulonia terrace, a transgressive conglomeratic body
resting on the complex Argille Varicolori formation
(p
reStininzi
, 1995).
Based on the above data, the following assump-
tion about the evolution of the slope was formulated.
In the time interval from 1000 to 950 ka, the Allaro
River must have incised the valley floor by about 100
m. Subsequently, a hiatus in the erosional process gave
rise to the surface lying at roughly 510 m asl. In this
stage, stream deepening is likely to have involved also
the terms of the metamorphic aureole, which are now
exposed on the slope at an elevation of 640 to 600 m
asl. The process of incision of the valley resumed in
the time interval from 950 to 900 ka, causing a further
deepening of about 60 m. A new break in the erosional
granites by using an alteration index (Ia%), i.e. the ratio
of altered feldspars to total feldspars. Moreover, a flow
of hydrothermal water with very low pH was observed
to control the distribution of Ia% (p
reStininzi
, 1984,
b
ArreSe
et alii, 2006). This control is witnessed by
plenty of surface features, such as a number of acidic-
pH (4.5<pH<5) springs located at the contact between
the basal crystalline terms and the overlying metamor-
phic ones (p
elleGrino
& p
reStininzi
; 2006). The sec-
tors of the granitic mass most affected by alteration lie
close to the heat-metamorphic contact aureole, where
highly or completely altered materials are found.
The predisposing factors for the DSGSD of Mt.
Granieri are: geological setting of the slope, occur-
rence of a rock mass at different stages of physico-
chemical alteration, regional uplift and incision by the
Allaro stream, which took place in successive steps.
The DSGSD may be attributed to a sackung process
(z
iSchinSkY
sensu, 1969) associated with large land-
slides (e.g. the one of 1972 at the topslope) (p
reStin
-
inzi
, 1984; p
elleGrino
, 2000), which accompanied the
more extensive deformational phenomenon (G
enevoiS
& p
reStininzi
, 1979a). Kinematic indicators are distrib-
uted along the different sectors of the slope. The top of
the slope is potentially unstable. It has a marked sack-
ung (z
iSchinSkY
, 1969) and consequent double crest,
i.e. the edge of the potential landslide scarp (Fig. 3).
The middle portion shows, instead, reverse slope con-
ditions (Piana di Monte Granieri plain), intensely frac-
tured areas due to concentration of shearing stresses,
concave-convex morphologies not related to landslide
debris (p
elleGrino
, 2000; m
Artino
et alii, 2004; p
el
-
leGrino
& p
reStininzi
, 2006) (Fig. 2b)
Fig. 3 - a) Top of the Mt. Granieri slope. The arrow points
to the double crest, visible in the upper part of
the relief, where the future landslide scarp will be
located; b) Rupture surface (and related detail)
along the internal Caulonia-Nardo di Pace pro-
vincial road. On the right-hand side, the monitor-
ing station whose location is shown in Fig. 2
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A. BRETSCHNEIDER, R. GENEVOIS, S. MARTINO, A. PRESTININZI,& G. VERBENA
126
International Conference on Vajont - 1963-2013 - Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
stresses σ
app
, applied as a percentage of the UCS
σ
0
on the related specimen. The laboratory-scale
curves built by G
enevoiS
& p
reStininzi
(1979b) are
reported in Figure 5. The time-dependent behaviour
of the specimens shows an instantaneous elastic de-
formation, a primary-creep portion with a decrease
of the strain rate vs. time, a secondary-creep portion
with an almost constant strain rate and, depending
on the percentage of stress applied, a tertiary-creep
portion with an accelerated strain rate, especially
under stresses close to the UCS. Tab. 1 summarises
the main physical and mechanical properties of the
tested specimens.
process thus formed the surface located at 450 m a.s.l.
The erosional activity of the stream resumed in the
time interval from 900 to 400 ka, when a new deep-
ening (of about 70 m) occurred. This long timespan
of about 500 ka must have been associated with other
erosional and depositional cycles, whose morphologi-
cal records were subsequently obliterated. A further
standstill must have caused the formation of the sur-
face located at 380 m asl, which was subsequently in-
cised in a period of at least 300 ka, giving rise to the
surface at about 300 m asl. In the period elapsed from
300 ka to the present, the Allaro River further downcut
its bed, reaching its current elevations (about 210 m
asl in the investigated sector). Figure 4 graphically de-
picts the reconstructed evolutionary model. The figure
shows the breaks in stream incision, correlating with
the terrace orders reported by m
iYAuchi
et alii (1994)
for the Serre Calabresi area.
METHODS
LABORATORY CREEP TESTS
Previous studies on the deep-seated gravitational
deformation of Mt. Granieri (G
enevoiS
& p
reStin
-
inzi
, 1979b) stressed the role of mass rock creep af-
fecting the slope. More specifically, the above-cited
study was focused on the interaction between extent
of alteration and visco-plastic behaviour of the de-
formed granitic mass. The study relied on a set of
creep tests on granitic rock specimens collected from
the slope; the specimens had different states of al-
teration, expressed by the alteration index, i.e. the
ratio of altered feldspars to total feldspars (Ia%).
The sampled alteration classes were considered to
represent the different states of alteration of granite
and the curves were built under different constant
Fig. 4 - Evolutionary-geological model of the Mt. Grani-
eri slope, highlighting the elevations of the strath
Allaro River terraces, which can be correlated
with the marine terrace reported by M
iyauchi
et
alii., 1994 for the Serre Calabresi area
Fig. 5 - Laboratory creep curves for different states of al-
teration at different percentages of UCS. As shown
in Table 2, the most altered classes are those of
specimens 3 and 4; specimens 5, 2 and 1 have
gradually lower states of alteration (G
enevois
&
P
restininzi
, 1979b)
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A PHYSICALLY-BASED SCALE APPROACH TO THE ANALYSIS OF THE CREEP PROCESS
INVOLVING MT. GRANIERI (SOUTHERN ITALY)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
127
(5.4 cm on average) was scaled up to three different
rock mass thicknesses (50, 150 and 300 m, respec-
tively) (Fig. 3), resulting into three scaled-up geometric
dimensions, varying with the depth and thickness of the
rock masses considered. These dimensions made it pos-
sible to apply the laboratory-tested rheological behav-
iour to portions of the slope with different dimensions.
The subsequent processes were the temporal upscal-
ing of laboratory creep tests on granite specimens with
different extent of alteration, and the viscosity scaling.
In this case, the dimensional relations were as
follows:
σ*=η*/ε* and t*=1/ε*
where σ* is the stress ratio, η* is the viscosity ratio,
ε* is the strain rate ratio, t* is the temporal ratio (ra-
tios of scaled system to real prototype). Table 2 gives
an example of the temporal upscaling of creep tests, in
this specific case on a specimen with alteration class 5
and a geometric scale ratio whereby the length of the
specimen corresponds to a rock thickness of 50 m. The
stress ratio was obtained via dimensional upscaling; the
viscosity ratio compared the viscosity values of granite
(measured by G
enevoiS
& p
reStininzi
, 1979b in their
creep tests) with the viscosity values of granite under
normal in-situ conditions. In the same material, viscos-
ity depends on its strain rate, which depends in turn on
the applied stress. In the creep tests, given the applied
stress and the unconfined condition of the specimen,
the measured viscosities proved to be much lower than
those of in-situ granitic rocks. The viscosity ratio may
be obtained by comparing these values. Strain rates and
thus temporal scale ratios may be compared by using
the viscosity ratio together with the stress ratio.
With the above-described approach, the experi-
mental creep curves built by G
enevoiS
& p
reStininzi
,
1979b were scaled up, considering for each specimen:
i) the different extent of alteration, and ii) the different
depths of interest (Figs 5a, b, c). Table 3 summarises
the scaling factors. Figures 5a, b, c provide the experi-
mental curves of specimens with different extent of al-
SCALING OF CREEP CURVES
The study experimented the scaling up of labo-
ratory results to the actual slope, by transposing the
creep tests conducted by G
enevoiS
& p
reStininzi
,
1979b to a spatio-temporal scale comparable to the
one of the actual slope.
The scaling approach resorted to the same rela-
tions as those used for small-scale physico-analogical
models of geological processes (h
ubbert
, 1937; r
Am
-
berG
, 1981; m
iddleton
& W
ilcock
, 1994; b
retSchnei
-
der
, 2010; b
ozzAno
et alii, 2013). Creep curves were
thus scaled by using dimensional equations based on
the relations between the scaled system and the real
prototype. In particular, the scaling consisted of two
steps: step 1 - spatial upscaling (scaling of geometric
dimensions) to define the stress scale ratio; step 2 -
temporal upscaling through the stress scale ratio and
the viscosity scale ratio.
Stress scaling was derived from the following di-
mensional relation:
σ*= ρ* ∙ g* ∙ l*
where: σ* is the stress ratio, g* is the gravity ratio
(g=1), l* is the length ratio (ratios of scaled system to
real prototype).
Additionally, laboratory curves were scaled by as-
suming three different geometric scale factors, in order
to take into account the involvement of a rock mass
within 300 m of depth (kinematically consistent with
ongoing deformations with respect to the geometry of
the present slope). The original length of the specimen
Tab.1 - Main physical and mechanical properties of sam-
ples with different states of alteration analysed by
G
enevois
& P
restininzi
(1979b)
Tab. 2 - Example of computation of the scale ratios for al-
teration class 5 at a depth of 50 m
Tab. 3 - Temporal upscaling factor for different sam-
ples at different depth intervals
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A. BRETSCHNEIDER, R. GENEVOIS, S. MARTINO, A. PRESTININZI,& G. VERBENA
128
International Conference on Vajont - 1963-2013 - Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
teration: specimen 2 (unaltered – Ia=25%), specimen
5 (averagely altered – Ia=37%) and specimen 4 (highly
altered – Ia=44%) scaled up to thicknesses of 50, 150
and 300 m. The upscaling of these curves yielded par-
ticularly significant results for better understanding
and describing the ongoing deformation of the Mt.
Granieri slope.
DISCUSSION
Results from the physically-based spatio-temporal
upscaling of laboratory creep tests made it possible to
determine the creep deformation stage that the granites
involved in the Mt. Granieri deformation had reached
at different depths and in the different stages of the
geomorphological evolution associated with the deep-
ening of the valley by the Allaro River.
Based on the reconstructed evolutionary model,
the gravitational deformations of Mt. Granieri origi-
nated during a standstill in the erosional activity of the
stream, corresponding to the strath surface which cor-
relates with 4
th
-order terraces (estimated date: about
950 ka), i.e. after incision of the contact between
heat-metamorphosed schists and underlying granites.
The aforesaid sector was affected by the 1972 rock
avalanche. Taking into account the alteration profiles
proposed for the slope by various authors (b
ArreSe
et alii, 2006; p
elleGrino
& p
reStininzi
, 2006; p
el
-
leGrino
, et alii 2008), the granites occurring in the
topmost portions of the Mt. Granieri slope are more
altered, as their measured Ia% values are higher (sam-
ple 4, Table 2). The investigated sector of the slope is
roughly 150 m-thick and the acting vertical stress is
estimated at roughly 3 MPa, corresponding to about
57% of the tensile strength determined for the samples
of the higher alteration class (sample 4, Tab. 2). This
condition coincides with the scaled-up creep curve of
Fig. 5a; therefore, the slope sector under review is at a
tertiary-creep stage (point A of Fig. 4 and 6a). Hence,
this condition is conducive to rupture phenomena, in-
cluding past landslides and evidence of ongoing frac-
turing and surface mobility, as previously observed by
various authors (p
reStininzi
, 1984; m
Artino
et alii,
2004; p
elleGrino
& p
reStininzi
, 2006; p
elleGrino
et
alii 2008). At greater depth, the less altered granites
have better mechanical properties (passage from the
alteration class of sample 4 to the alteration class of
samples 5 and/or 3). In this case, the scaled-up refer-
ence curves are as shown in Fig. 5b. The stresses act-
ing in situ at these depths are equal to approximately
5.5 MPa, equal to about 60% of the UCS determined
for the samples of alteration class 5. Hence, also in
this case, considering an evolution time of about 500
ka, or starting from the formation of the strath surface
corresponding to the 4
th
-order marine terrace, granites
are at an incipient stage of deformation due to tertiary
creep (point B of Fig. 6b). This condition applies to
Fig. 5a - Creep curves for sample 2 (unaltered) of Tab. 2
(three depth intervals) scaled down to the dimen-
sion of the slope
Fig. 5b - Creep curves for sample 5 (averagely altered) of
Tab. 2 (three depth intervals), scaled down to the
dimension of the slope
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A PHYSICALLY-BASED SCALE APPROACH TO THE ANALYSIS OF THE CREEP PROCESS
INVOLVING MT. GRANIERI (SOUTHERN ITALY)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
129
Likewise, in the more downhill sector of the slope,
deformation must have started not before the forma-
tion of the strath surface correlating with the 7
th
-order
marine terrace (Fig. 4), i.e. about 300 ka. Even the as-
sumption of the worst granite alteration conditions for
this sector (alteration class 5) and of a depth of 300
m from ground level (consistent with the kinematics
of the deformational process) cannot justify a tertiary-
creep stage for the rock mass under review. In fact, as
shown in Figs 4 and 6b (point D), the granitic rock in
this sector of the slope is at a secondary-creep stage.
CONCLUSIONS
This study experimented a physically-based ap-
proach to scale up laboratory creep tests to the spatio-
temporal evolution of a natural slope and thus to assess
the different creep stages of its current deformations.
The approach was tested on the case study of Mt. Grani-
eri (Calabria, Italy). For this area, results from creep
tests carried out on rock samples taken from the slope
and with different states of alteration were available.
In spite of uncertainties associated with the above
assessment, the results obtained with this approach
proved to be consistent with the case study. The trans-
position of rock mass stresses to the scaled curves
indicated tertiary creep-induced deformations; these
deformations are demonstrated on site by monitor-
ing surveys and by clear morphological evidence. The
both altered and unaltered granites at the top of the
Mt Granieri slope. In more detail, this tertiary creep
is already at an advanced stage in the first 150 m of
thickness, where it mostly involves altered granites,
whilst it is incipient within 300 m of thickness, where
it involves poorly altered granites.
It is worth emphasising that a monitoring survey
of the investigated slope is still under way. The survey
is based on data recorded by inclinometer probes in-
stalled at different depths (down to 35 m from ground
level) in the top part of the investigated slope, at the
Piana di Monte Granieri plain (Fig. 2). The strain rates
measured so far during the survey (P
elleGrino
, 2000;
p
elleGrino
et alii, 2008) are about two orders of mag-
nitude higher than those obtained from creep curves.
This finding infers a deformational process that has al-
ready exceeded rupture conditions and the fact that the
shallowest portions of the landsliding slope are subject
to rainfall-induced accelerations, as highlighted by
previous studies (p
elleGrino
et alii, 2008).
In the intermediate sector of the slope, whose mor-
phological evolution started not before 400 ka, the sit-
uation is as shown in point C of Figs 4 and 6b. In this
instance, even considering conditions more conducive
to creep and thus the worst alteration class (class 5)
for these sectors and a depth of 300 m, the crystalline
rock is at a secondary-creep stage and its strain rate is
constant over time.
Fig. 5c - Creep curves for sample 4 (highly altered) of Ta-
ble 2 (three depth intervals) scaled down to the
dimension of the slope
Fig. 6 - Plausible creep stages for granites outcropping
at the top (points A and B of Figure 4) of the Mt.
Granieri slope and in the valley floor (points C
and D of Figure 4). The dashed line in blue in a)
is the result of an interpolation made to obtain the
values for a percentage of UCS of 57%.
Point A: creep stage at 950 ka and 50 m of depth.
Point B: creep stage at 950 ka and 300 m of depth.
Point C: creep stage at 400 ka and 300 m of depth.
Point D: creep stage at 300 ka and 300 m of depth
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A. BRETSCHNEIDER, R. GENEVOIS, S. MARTINO, A. PRESTININZI,& G. VERBENA
130
International Conference on Vajont - 1963-2013 - Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
mass thicknesses (still consistent with the kinematics
of slope deformations), only stationary-creep condi-
tions are plausible.
The deformational scenario elucidated by this
study may trigger a new large landslide (mobilising an
estimated volume of 1 Mm
3
), as an evolution of the
phenomena that have historically affected the topslope
and, in particular, as a retrogression of the 1972 rock
avalanche (mobilising a volume of rock mass estimat-
ed at about 2Mm
3
).
phenomenon started about 950 ka in the topmost por-
tions of the slope down to depths of 150-300 m from
the topographic surface, affecting highly to poorly al-
tered granitic rocks underlying the contact with heat-
metamorphosed schists. The scaled-up creep curves
also infer that the temporal evolution of valley deep-
ening by the Allaro River does not justify similar creep
stages in the lower portion of the Mt. Granieri slope.
Here, even on the assumption of the worst alteration
conditions for granitic rocks and of the highest rock
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A PHYSICALLY-BASED SCALE APPROACH TO THE ANALYSIS OF THE CREEP PROCESS
INVOLVING MT. GRANIERI (SOUTHERN ITALY)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
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