New landslides susceptibility mapping method

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 6, Issue 1, January (2015), pp. 161-171 © IAEME
161
NEW LANDSLIDES SUSCEPTIBILITY MAPPING
METHOD: A CASE STUDY
Robert Nini
Civil engineering department, University of Balamand, El Koura, Lebanon,
ABSTRACT
Many impressive landslides have recently occurred in the world causing serious damages for
infrastructure facilities and buildings. A prediction based on the susceptibility mapping will be of
such importance in order to reduce their damages. Our work constitutes a first attempt of mapping the
landslides susceptibility by a method which a compromise between the two known approaches: The
expertise method and the analytical method. Manylandslidesoccured in Lebanon, causing destructive
damages to the transportation infrastructure and agricultural territory.A first data on these landslides
and their permanent causes are presented based on the existing documents and soil investigations
campaigns. Our study is based on the analysis of different causal factors of these landslides, such the
geology, slope, hydrogeology, soil, tectonic, pluviometry and vegetation. This study permits to map
the critical modalities of different causal factors. The superposition of these maps of different factors
will be beneficial to localize the zones presenting high risk of instability.
Keywords: Causal Factors, Landslides, Risk Map, Susceptibility Study, Critical Modality.
1. INTRODUCTION
From a long time, the soil movements are one of the most known geodynamical process in the
world [1]. The increasing of the victims’ number is related to the increasing of population especially
close to the zones presenting some instability risks. In the United States, the landslides took place
everywhere and their damages to the building and infrastructure reaches annually more than 2
billions of dollars with 20 to 50 victims [2] [3]. The international federation of the Red Cross counted
more than 1550 victims per year between 1969 and 1993[4].
Landslide hazard prediction is necessary in order to reduce these damages. This prediction
based on the risk mapping should permit to limit the landslides risks, limit and not cancel because
eliminating the risk is almost impossible.
During the last thirty years, many technics were proposed for the slope stability study. Three
main approaches are known for this study: Expertise approach, statistical approach and analytical
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ISSN 0976 – 6308 (Print)
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162
approach. Our work constitutes the first attempt for landslide susceptibility mapping by a method
which is a compromise between the first and third method.
Lebanon which is a mountainous zone is widely concerned by the landslides. These landslides
have social and economic impacts because they are responsible of directly or indirectly considerable
damages.
Landslides inspection based on analysis of factors affecting the stability may offer very
important informations in order to predict them. Risk maps could be drawn by using aerial photos,
topographical and geological plans and by taking into consideration the history of the region in terms
of landslides. In order to reduce the large damages resulted from these soil movements, a long term
prediction will be necessary. Complete risk elimination is in most cases impossible but these risk
maps can limit the risks of landslides. These maps help to localize the zones with a high possibility of
sliding but the date still always unknown. In this case, if climatological informations as pluviometry
rate and seismic informations as seismic scale of the regions could be added to these plans, we can
create a time factor which could refine the probability of landslide occurrence.
II.CASE STUDY
Some impressive landslides took place in Lebanon recently. The mountainous topography and
the high pluviometry are between the main reasons of slope instability.
They took place in the zone of Mount Lebanon which is located between 800 m and 1800 m
altitude and receives a pluviometry ranging between 1100 and 1700 mm. this zone is characterized
by vegetation consisting of apple trees, peaches and prunes. From seismic point view this zone is
well known by its high seismic activity due to the fact that it is limited on east by the main fault of
Yammouneh which is an extension of the Red Sea fault and by the west by many minor faults.
The scale of these landslides ranges from hundreds to thousands meters. All the landslides in
Lebanon have as triggering factor the gravity. When the geological, morphological and structural
conditions are favorable for soil movements with the gravity factor, a landslide took place. These
conditions are grouped in two families, the permanent factors and the triggering factors. The
triggering factor of majority of Lebanese landslides is the excess of pluviometry. We studied five
impressive landslides:
2.1 EsSfireh Landslide
This landslide is located at 42 kilometers from Tripoli, the capital of North Lebanon.
Geologically, the slided zone consists of volcanic and sedimentary soil dating from the cretaceous
period. Tectonically two local faults are found in the region. From hydrogeogically point view, a very
strong water spring is found at 5 kilometers of the slided zone. This zone receives a pluviometry
ranging between 1000 to 1500 mm of rain. The soil consists of 10 meters of superficial sandy clay
with gravel, having plasticity between 17 to 24 % which rests on fractured limestone with fractures
filled by clay.
2.2 Becharreh-Ceadars Landslide
This landslide is located at south-east of Tripoli between the village of Becharreh and the
famous Lebanese cedars zone and close to “Qornet el sawda” the highest point in Lebanon with 3038
m. altitude. Geologically, the site is composing of an upper quaternary colluvium deposit which in
turn laying on superposition of clayey and limestone formations. Both layers are resting on formation
of black basalt moderately fractured. According to the tectonic map of Lebanon, any important fault
was found close to the slided zone. From hydrogeological point view, this landslide is located in a
zone of local water table which was verified by many boreholes done on this zone. The climate is
rude with 1250 mm of rain with vegetation consisting of apple trees. The soil consists of a layer of

163
clayey silt, sand and gravel having thickness of 5 to 15 m. The upper part of this layer is
characterized by weak plasticity in contrast to the lower part which has an average to high plasticity.
This layer is resting on black basaltic formation moderately fractured.
2.3 Aaqoura Landslide
This landslide is located to the north of Mount Lebanon and at 80 km north east of Beirut.
The slided zone has 3500 m length and 500 m width. Geologically, the formations date from the
upper Jurassic till Cenomanian. From hydrogeologically point view, the zone has local water table,
despite this, the people tried many times to dig wells without reaching water level. This zone receives
the highest rate of pluviometry in Lebanon which ranges between 1500 to 1700 mm.The soil profile
is composed of inorganic clay soil with average to high plasticity of around 20 meters thickness
laying on limestone rock.
2.4 Daher el Baidar Landslide
This landslide is located in Daher el Baidar zone on east of Beirut. Geologically, the upper
layer consists of residual soil resting on layer of clay and limestone from Cretaceous period. Many
minor faults are distributed around the slided area. According to the hydrogeological map, this zone
is located in zone with local water table. The same zone receives annually between 1250 and 1650
mm of rain and covered by bushes. From geotechnical point view, the soil consists of superficial
deposit consisting of mix of silty clay and clayey gravels of 2 meters thickness. This formation rests
on alternation of sandy clay and limestone formations. The sandy clay has a plasticity index ranging
between 10 to 19 %.
2.5 Kfarfaqoud Landslide
During winter 2002, a landslide was localized at the top of the village of kfarfaqoud, situated
at the south east of Beirut. Geologically, the slided zone is located on formations which date from the
Cretaceous period. This landslide is located in Mount Lebanon and the fault of Yammouneh
separates it from the Bekaa valley. This fault is considered as continuity of the Dead Sea fault which
is responsible about almost all the earthquakes happened in Lebanon. From hydrogeological point
view, this zone is classified as zone with local or discontinues water table. The mentioned zone
receives annually about 1125 mm of pluviometry and it is covered by bushes and some trees. From
geotechnical point view, the soil consists of an upper layer of heterogeneous sandy clay of PI
between 16 to 26 % with thickness till 16 meters. This layer is resting on highly fractured limestone
and claystone.
III. LANDSLIDES FACTORS MAPPING
The analysis of the causal factors and their threshold in the slided zones in Lebanon lead us to
divide each factor map to three types of zones:
a- zones where this factor leads to an important risk of sliding,
b- zones where this factor leads to an average risk of sliding,
c- zones where this factor leads to an almost no risk of sliding.
Each type of zone is called modality; we have three modalities A, B and C for each factor.
3.1 Geology Factor Mapping
The sedimentary formations are dominants in Lebanon especially in Mount Lebanon. The
modalities adopted are:
a- Modality A: Soft formations
b- Modality B: Heterogeneous formations, alternation of marl and beds of fine limestone

International Journal of Civil Engineering
ISSN 0976 – 6316(Online), Volume 6, Issue 1, January (2015), pp.
c- Modality C: Homogeneous and massive formations
By looking on the geological map of Lebano
dominant in Lebanon. It is the modality which present
landslide of Becharreh-Cedars is situat
geology of the most slided zones in Lebanon is hatched horizontally
Lebanon [5]. The names of the landslides located on the map from up to down are as follows: Es
Sfireh, Becharreh-Cedars, Aaqoura, Daher el Baidar and Kfarfaqoud.
3.2 Slope Factor Mapping
The role of the slope in land
limits for which the slope will be classified gentle, average or steep. These values are relative for
each type of geological formations. The reason behind choosing 15 and 30 degrees as lower and
upper limits for average slopes is that thi
the heterogeneous formations in Lebanon especially that the formations
than 15 degrees are soft. For our case, we ar
the three modalities are:
a- Modality A: Steep slope: Slope > 30 degrees
b- Modality B: Average slope:10 degrees < Slope < 30 degrees
c- Modality C: Gentle slope: Slope < 10 degrees.
By looking on the slope of the five landslides, we notice tha
Fig. 1 Mapping of modality B of factor geology with the location of five landslides
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976
6316(Online), Volume 6, Issue 1, January (2015), pp. 161-171 © IAEME
164
Modality C: Homogeneous and massive formations
By looking on the geological map of Lebanon, we noticed that the modality B
dominant in Lebanon. It is the modality which presents the largest rate of slide
dars is situated in modality C. The modality B which
geology of the most slided zones in Lebanon is hatched horizontally (fig. 1) on the geological map of
The names of the landslides located on the map from up to down are as follows: Es
Cedars, Aaqoura, Daher el Baidar and Kfarfaqoud.
The role of the slope in landslide occurrence is evident. The problem is to
is that this threshold is representative for the majority of the slopes of
formations in Lebanon especially that the formations which have
than 15 degrees are soft. For our case, we are mapping the heterogeneous formations, for this
Slope > 30 degrees
verage slope:10 degrees < Slope < 30 degrees
entle slope: Slope < 10 degrees.
By looking on the slope of the five landslides, we notice that they are located in modality B
Mapping of modality B of factor geology with the location of five landslides
and Technology (IJCIET), ISSN 0976 – 6308 (Print),
© IAEME
that the modality B is relatively
largest rate of slided areas. Only the
which presents the type of
n the geological map of
The names of the landslides located on the map from up to down are as follows: Es-
. The problem is to define the slope
s threshold is representative for the majority of the slopes of
which have slope smaller
formations, for this reason
located in modality B.
Mapping of modality B of factor geology with the location of five landslides

165
EsSfireh and Aaqoura landslideshave 11 degrees as slope, Daher El Baidar 13 degrees, Kfarfaqoud
15 degrees and Becharreh-Cedars 22 degrees.
We hatched vertically the zones with modality B(Fig. 2) on the topographical map of Lebanon
3.3 Hydrogeology Factor Mapping
The geological structure of Lebanon plays an important role for his hydrogeological aspect. In
fact, the massive permeable limestone formations which works as water reserve occupies three
quarter of Lebanon area. Based on the hydrogeological map of Lebanon, we divided the water tables
in three types:
a- Modality A: zones with continuous ground water table
b- Modality B: zones with local or discontinuous ground water table
c- Modality C: Zones without ground water table or very local water table
The majority of the landslides are located in zones showing the modality B, therefore we
hatched the modality B, NE-SW (Fig. 3) on the hydrogeological map of Lebanon [6].
Fig. 2. Mapping of modality B of factor slope with the location of five landslides

166
3.4 Soil Factor Mapping
The majority of the slided soil had a major part consisting of clay with low to medium
plasticity. We divided the soil type to three modalities,
a- Modality A: Clayey soil, peat soil, alluvium, colluvium
b- Modality B: Red soil (terra rosa) on compacted limestone, grey soil on basalt formations
c- Modality C: Mountainous yellow soil
Based on the soil map [7], we hatched SE-NW the modality A since that the majority of the slided
soil verify this modality (Fig. 4).
Fig. 3. Mapping of modality B of factor hydrogeology with the location of five landslides
3.5 Tectonic Factor Mapping
We used the geological map of Lebanon where all the majors and minors faults majors are
shown. The major fault of yammouneh is dividing Lebanon to two zones, one to the west of the fault
where most of the minor faults are located, and the other to the east with too much less faults. We
assume that if the slided zone is located not far from 1 km from the fault, is affected by the fault
a- Modality A: Zone with major fault
b- Modality B: Zone with local or minor fault
c- Modality C: Zone without fault
The following figure shows the minor and major faults in Lebanon (Fig. 5).

Fig. 4. Mapping of modality A of factor soil with the location of five landslides
3.6 Pluviometry Factor Mapping
An evident link exists between pluviomatry rate and the occurrence of soil movements. In
fact, the five landslides are located in zones with a pluvio
The proposed modalities are:
a- Modality A: Pluviometry rate larger than 1000 mm
b- Modality B: 500 mm <Pluviometry rate < 1000 mm
c- Modality C: Pluviometry rate less than 500 mm.
We hatched the modality A (Fig. 6) on the
3.7 Other Factors Mapping
Regarding the uniformity of the vegetation type which consists of bushes for almost all the
slided areas, this factor was not mapping.
167
Mapping of modality A of factor soil with the location of five landslides
Mapping
fact, the five landslides are located in zones with a pluviometry rate more than 1000 mm.
Pluviometry rate larger than 1000 mm
Modality B: 500 mm <Pluviometry rate < 1000 mm
Modality C: Pluviometry rate less than 500 mm.
We hatched the modality A (Fig. 6) on the pluviometric map of Lebanon [8].
slided areas, this factor was not mapping.
© IAEME
Mapping of modality A of factor soil with the location of five landslides
metry rate more than 1000 mm.

Fig. 5. Mapping of factor tectonic with the location of five landslides
IV. LANDSLIDE SUSCEPTIBILITY RISK MAPPING
The superposition of the six map factors
regarding a uniform vegetation and important pluviometry
zones with five, four and three superposed factors are presented (Fig. 7). We faced the problem of
map scale which is relatively small 1:200.000.
The position of the five mentioned landslides relatively to the zon
modalities is as follows (Fig. 8):
Es-Sfireh landslide is situated in a zone having six superposed factors with critical modalities as:
geology, soil, hydrogeology, slope, pluviometry and tectonic
Becharreh-Cedars landslide is situated in a zone having four superposed factors with critical
modalities as: slope, hydrogeology, soil and pluviometry
Aqoura landslide is situated in a zone having five superposed factors with critical modalities as:
geology, hydrogeology, soil, slope and pluviometry
Daher el Baidar landslide is situated in a zone having four superposed factors with critical modalities
as: slope, geology, pluviometry and tectonic
168
Mapping of factor tectonic with the location of five landslides
IV. LANDSLIDE SUSCEPTIBILITY RISK MAPPING
The superposition of the six map factors with critical modalities for our five landslides
a uniform vegetation and important pluviometry permits to obtain the following map where
map scale which is relatively small 1:200.000.
the five mentioned landslides relatively to the zones of different superposed
Sfireh landslide is situated in a zone having six superposed factors with critical modalities as:
geology, soil, hydrogeology, slope, pluviometry and tectonic (Dark Blue).
ndslide is situated in a zone having four superposed factors with critical
modalities as: slope, hydrogeology, soil and pluviometry(Blue)
landslide is situated in a zone having five superposed factors with critical modalities as:
geology, hydrogeology, soil, slope and pluviometry(Green).
as: slope, geology, pluviometry and tectonic (Blue)
© IAEME
Mapping of factor tectonic with the location of five landslides
with critical modalities for our five landslides
permits to obtain the following map where
es of different superposed
Sfireh landslide is situated in a zone having six superposed factors with critical modalities as:
ndslide is situated in a zone having four superposed factors with critical
landslide is situated in a zone having five superposed factors with critical modalities as:

Fig. 6: Mapping of factor pluviometry with the location of five landslides
Kfarfaqoud landslide is situated in a zone having five superposed factors with critical
modalities as: slope, hydrogeology,
The five studied landslides are located in
The combinations of different factors for the five landslides are presented in Table 1:
Table 1: Combination of Different Factors for the Five L
Geology
Es-Sfireh B
Becharreh-Cedars C
Aqoura A
Daher El Baidar B
Kfarfaqoud B
169
Mapping of factor pluviometry with the location of five landslides
slope, hydrogeology, geology, pluviometry and tectonic (Green)
The five studied landslides are located in zones of four to six superposed factors.
Table 1: Combination of Different Factors for the Five Landslides
Geology Slope Hydrogeology Soil Pluviometry
B B A A
B B A A
B B A A
B C C A
B B C A
© IAEME
Mapping of factor pluviometry with the location of five landslides
(Green)
zones of four to six superposed factors.
andslides
Pluviometry Tectonic
B
C
C
B
B

170
Fig. 7. Superposition of five factors, geology, slope, hydrogeology, soil and tectonic with the location
of five landslides
V. CONCLUSION
This methodconstitutes a first attempt of mapping the landslides susceptibilityin Lebanon for
heterogeneous formations by a method which is a compromise between the expertise method and the
analytical method. In fact, the number of parameters involved in the behavior of unstable slope
makes useless the using of analytical method based only on calculation.
These plans could be very interesting for territories long term planning work. The study and
analysis of causal permanent factors permit to obtain these risk maps. Not to forget that this method
presents some limitations but it will be always simple, practical and general method.

171
Fig. 8. Zones of six, five and four superposed factors of critical modalities with the location of five
landslides
REFERENCES
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2. W.B. Creath, Home buyers guide to geologic hazards: Arvada, Colorado (Colorado:
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3. E.B. Nuhfer, P.H. Proctor and P.H. Moser, The citizens guide to geologic hazards:Arvada,
Colorado (Colorado: American Institute of Professional Geologist, 1993)
4. R. Hamilton, Report on early warning capabilities for geological hazards (USA: IDNDR
Scientific and Technical Committee, 1997)
5. L. Dubertret, Geological map of Lebanon (Beirut: Ministry of public works, 1955)
6. United Nations, Hydrogeological map of Lebanon (Beirut: Ministry of public works, 1967)
7. B. Geze, Soil map of Lebanon (Beirut: Ministry of Agriculture, 1956)
8. J. Ray, Pluviometric map of Lebanon (Beirut: Ministry of Public works, 1984)
9. Rasheed Saleem Abed, “Experience on Using Total Station Surveying For Mapping and
Contouring” International Journal of Civil Engineering & Technology (IJCIET), Volume 4,
Issue 3, 2013, pp. 155 - 167, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.
10. Jimmy Kansal, Neeti Jain, PK Satyawali, Ashwagosha Ganju, “Competency Mapping In
Knowledge Based Organizations” International Journal of Management (IJM), Volume 3,
Issue 2, 2012, pp. 279 - 290, ISSN Print: 0976-6502, ISSN Online: 0976-6510.

New landslides susceptibility mapping method

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