Indian Geotechnical Conference (IGC-2010)igs/ldh/files/igc 2015 pune... · thus has the potential to be used in an early warning system against landslide hazard. The variation of

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INDIAN GEOTECHNICAL CONFERENCE

17th

– 19th

DECEMBER 2015, Pune, Maharashtra, India

Venue: College of Engineering (Estd. 1854), Pune, India

LANDSLIDE EARLY WARNING BASED ON GEOTECHNICAL SLOPE STABILITY

MODEL FOR THE GUWAHATI REGION

Chiranjib Prasad Sarma1, Arindam Dey

2, A. Murali Krishna

3

ABSTRACT

Landslides constitute a significant geohazard within the region of Guwahati city, rainfall being the

triggering factor for such occurrences. Comparison of historical records of rainfall and landslides in the

hill slopes of Guwahati highlights and establishes this correlation. The impact of rainwater infiltration in

causing landslides is widely recognized. Rainfall infiltration results in increase in the water content and

decrease in the matric suction thereby raising the unit weight and reducing the shear strength of soil in the

colluvium of the landslide. Hill slopes within the city of Guwahati consist of residual soils, often in

unsaturated condition, and therefore the conventional saturated soil mechanics approach to assessing the

stability of these slopes is inadequate. To assess the potential susceptibility to rainfall-induced landslide,

an effective modeling of changes in water content and matric suction in response to rainfall infiltration is

essential.

Speedy and unplanned urbanization within the city of Guwahati due to the phenomenal influx of

population over the past four decades have resulted in continuous conversion of land from non-urban use

to urban use, leading to rampant encroachment and earth-cutting on the hillslopes. Shrinkage of forest

cover has bought about a change in the surface and sub-surface hydrology. Economical incapacitated

societies are increasingly reluctant to invest money in structural measures that can reduce this natural risk.

Hence, the new issue is to implement a reliable decision support based on early warning systems aimed at

minimizing the loss of lives and property without investing in long-term, costly projects of ground

stabilization. The precursor to development of such a system is to quantify the correlation of landslide

occurrences to the destabilizing factors.

Geotechnical slope stability models are capable of providing detailed description of potential instability

under changing environmental and climatic conditions and are able to establish threshold values of the

triggering phenomenon; however, they are only rarely incorporated into landslide early warning systems.

1Chiranjib Prasad Sarma, Research Scholar, Indian Institute of Technology Guwahati, India, [email protected]

2Arindam Dey, Assistant Professor, Indian Institute of Technology Guwahati, India, [email protected]

3A. Murali Krishna, Associate Professor, Indian Institute of Technology Guwahati, India, [email protected]

mailto:[email protected]



Chiranjib Prasad Sarma, Arindam Dey & A. Murali Krishna

In the context of constructing early warning systems in regions where extensive data on landslide

occurrences and associated rainfall are inexistent, such tools offer the possibility to establish thresholds

for measurable geotechnical parameters.

This study constitutes an investigation into the infiltration processes, and the mechanism leading to

reduction in hill slope stability. Seepage analysis is performed using SEEP/W for transient/steady state

conditions considering saturated / unsaturated material model and the computed pore-water pressure are

then used in SLOPE/W to evaluate the changes in stability with time applying limit equilibrium methods.

Two homogenous and isotropic slopes of height 30 m with an inclination of 45⁰ (1H:1V) and assigned

properties of residual soil typical to the hillslopes of Guwahati region was assumed for the analysis.

Rainfall infiltration consistent to storm events prevalent in this region has been considered and the factor

of safety of the slopes are evaluated and plotted against time. Figure 1 (a) gives the rainfall data of the

storm event of 4th

– 7th

October, 2004, while Figure 1 (b) gives the degradation of the stability condition

in the form of reducing factor of safety.

Fig. 1(a) Rainfall storm event history (afternoon of

4th October to the midnight of 7th October, 2004)

Fig. 1(b) Corresponding factor of safety vs. time

for slope composed of reddish silty clay (RS) and

pale yellow silty sand (PYS)

The study highlights the importance of considering the behavior of unsaturated soil in analysis and

predicting the stability of unsaturated residual soil slopes. Numerical transient seepage and slope stability

analysis was able to quantify the effect of infiltration on the stability of such natural slopes with time and

thus has the potential to be used in an early warning system against landslide hazard. The variation of

safety factor of the slope with time can be provided as a basis to develop method for the real-time

prediction of the rain-induced instability of slopes. However the analysis results depends greatly on the

input parameters and thus extensive field investigations, laboratory soil testing, and rainfall data needs to

be collected.

Keywords: Landslide early warning, Slope Stability, Rainfall Infiltration, Seepage, Permeability, Matric

Suction, SEEP/W, SLOPE/W

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LANDSLIDE EARLY WARNING BASED ON GEOTECHNICAL SLOPE

STABILITY MODEL FOR THE GUWAHATI REGION

Chiranjib Prasad Sarma, Research Scholar, Indian Institute of Technology Guwahati, [email protected]

Arindam Dey, Assistant Professor, Indian Institute of Technology Guwahati, [email protected]

A. Murali Krishna, Associate Professor, Indian Institute of Technology Guwahati, [email protected]

ABSTRACT: Rainfall-triggered landslides are a major geohazard in Guwahati region which cannot be

convincingly addressed by conventional slope-stability approaches. This study attempts to address this issue with

the help of advanced analysis considering the concepts of unsaturated soil mechanics involving transient/steady

state phenomenon aided by the variation of pore-water pressures for providing a predictive model for the potential

instability under rainfall infiltration process. It is observed that the matric suction and its effect on the variation of

permeability and degree of saturation along with the intensity and duration of rainfall event are critical factors in

assessing the state of instability.

INTRODUCTION

Historical records of landslide events suggest that

the phenomena in the Guwahati region are rain–

triggered. All landslides were reported to occur

when monsoon is at its peak or nearing completion,

i.e., by the month of July-August to the end of

September to mid-October [1,2]. A total

cumulative rainfall of 750 mm over three days,

between 5th

and 8th

October 2004, triggered many

landslides around Guwahati hillslope areas,

causing death of 17 persons and destruction to

property worth millions of rupees. The same storm

event triggered as many as 100 landslides of

varying dimensions along NH 44, Guwahati-

Shillong road within a reach of 80 km [3]. In the

month of June, 2012, several landslides occurred,

triggered by intense rainfall events throughout the

month.

Speedy and unplanned urbanization within the city

of Guwahati due to the phenomenal influx of

population over the past four decades have resulted

in continuous conversion of land from non-urban

use to urban use, leading to rampant encroachment

and earth-cutting on the hillslopes. Shrinkage of

forest cover has bought about a change in the

surface and sub-surface hydrology. Economical

incapacitated societies are increasingly reluctant to

invest in structural measures that can reduce this

natural risk. Hence, the new issue is to implement a

reliable decision support based on early warning

systems aimed at minimizing the loss of lives and

property without investing in long-term, costly

projects of ground stabilization. The precursor to

development of such a system is to quantify the

correlation of landslide occurrences to the

destabilizing factors.

The impact of rainwater infiltration in causing

landslides is widely recognized [4,5,6,7]. Rainfall

infiltration results in increase of the water content

and decrease in the matric suction thereby raising

the unit weight and reducing the shear strength of

soil within the colluvium of the landslide. Hill

slopes within the city of Guwahati consist of

residual soils in an unsaturated state [8,9],

therefore the conventional soil mechanics approach

in assessing the stability of these slopes proves to

be inadequate. To assess the potential susceptibility

to rainfall-induced landslide, an effective

modelling of changes in water content and matric

suction in response to rainfall infiltration is

essential.

Geotechnical slope stability models are capable of

providing detailed description of potential

instability under changing environmental and




climatic conditions and are able to establish

threshold values of the triggering phenomenon;

however, they are only rarely incorporated into

landslide early warning systems. Several studies

concerning rainfall, infiltration and landslide

mechanism can be found in literature. Numerical

models were developed to study the variation of

infiltration in a slope with respect to rainfall

intensity and its effect on the slope stability

[10,11,12,13]. Moreover, in the context of

constructing early warning systems in regions

where extensive data on landslide occurrences and

associated rainfall are inexistent, such tools offer

the possibility to establish thresholds for the

measurable geotechnical parameters [14].

Before being able to conduct such an analysis

proper characterization of the behaviour of the

unsaturated residual soils is essential. However,

severe limitation is observed as far as literature

pertaining to characterizing the unsaturated soil

behaviour of this region is concerned. The study

attempts to apply unsaturated soil mechanics

approach for explaining the rainfall induced

landslides in this region with whatever limited

literature is available.

STUDY AREA

Location and Topography

Guwahati falls approximately within latitude

(91⁰33' – 91⁰52'6'') E and longitude (26⁰4'45'' –

26⁰14') N, with an approximate area of 328 sq. km

spread across both banks of the river Brahmaputra

[15].

Hills composed of residual soils, dotting around the

alluvial plains and the marshy wetlands, mainly

comprises of three prominent geomorphological

features that can be easily identified. The hills,

ranging in altitude of 100–300 meter are

interspersed among elongated low–lying alluvial

plain with varying altitudes of 49–56 meter above

mean sea level (MSL). The hillslope angles varies

from a gentle slope of 10⁰ to as steep as 70⁰ [16].

Geology

Gneiss and granite bodies affected by joints,

intruded by quartz–feldsphetic veins, aplite dykes

and pegmatite constitute the hills in this region.

Thin bands or lenses of quartzite, amphibolites and

biotite schists, are found parallel to the foliation

[17,18,19,20]. Physical and chemical weathering

process on the parent rock vis., granite, gneiss and

porphyritic granite produce the residual soils of

this region. Concluding from field investigation,

two types of commonly found overburden residual

soils constituting the hill slopes around Guwahati

are reported in literature [8,9]. A top laterite

formation of reddish residual silty clay is observed,

varying in thickness from few centimetres to few

meters, underlain by a saprolite formation of pale

yellowish residual soil, which has been classified

by the researchers as a poorly graded silty sand.

Photograph 1 Soil profile of a cut slope at the IIT

Guwahati Campus

Saprolite formation is the layer of residual soil

derived from isovolumetric weathering of the

bedrock and retains much of the parent rock

structure and fabric but with a much lower density.

Thus, undisturbed saprolite formation looks very

compact but actually is very porous and friable and

can be easily crumbled with minimum of effort.

Saprolite formations when exposed to profuse

rainfall infiltration can lose the clayey fraction

through the seepage of water leading to loss in the

cohesive component of shear strength [4,21,22].

Residual soil layers, up to depth of 30 m from bed

rock [8,9,16] are commonly formed in the zones of

well drained regions, while in the zones of

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moderate, imperfectly and poorly drained regions

erosion and mantle stripping occurs, leading to

exposed rock layers and formation of etchforms

and inselbergs. A typical formation of the soil type

is shown in Photograph 1 as obtained from a hill

slope excavation at IIT Guwahati.

The North Eastern Region of India experiences

heavy rainfall during the monsoon season spread

across the month of April to September. The

wetting cycle starts from the month of April to mid

of October and drying cycle starts from of

November up to March, March being the hottest

and driest month of the year. High evaporation rate

during the drying cycle leads to the development of

high matric suction in the hilly areas covered by

residual soils around Guwahati. This phenomenon

enables the soil slopes to remain stable at much

steeper angles. However, during monsoon season,

infiltration of rain water into the soil slopes brings

about a reduction in the matric suction and

ultimately may lead to slope failures [8,9].

There is a lack of attention to this issue from an

analytical standpoint. The major difficulty is the

assessment of the soil behaviour in the unsaturated

state. Understanding of unsaturated soil behaviour

and more importantly assessing the unsaturated soil

parameters is imperative in formulating a correct

analytical solution to the problem. In order to

determine the decrease of the suction pressures, the

relationship between the negative pore–water

pressure of the soil and the water content, referred

to as soil–water characteristic curve (SWCC) is

required and can be obtained through laboratory

test. However most of these methods are costly and

time intensive and would require skilled personnel

for its measurement. More difficult than that is to

experimentally obtain the unsaturated hydraulic

conductivity curve (UHCC), which gives the

relationship of soil permeability with matric

suction. The shear strength parameters of

unsaturated soils which require suction controlled

direct shear or triaxial test to be conducted, which

is another impasse towards the solution of this

problem. Exhaustive treatises on unsaturated soil

mechanics are found in literature but only a

handful of them are concerned to the soils found in

this region.

Soil Parameters Adopted for this Study

Literature [8,9] presents the properties of the

unsaturated soil properties of typical residual soils

(RS - Red Silty Clay, PYS - Pale Yellow Silty

Sand) commonly found in the hill slopes of

Guwahati and the same is been adopted in this

study. Table 1 gives the index properties of the

soils, while the relevant geotechnical parameters

adopted for this study are presented in Table 2.

Table 1 Index properties of the soils used in this study [8,9]

Property (RS) (PYS)

Colour Reddish Light

Yellowish

Specific Gravity 2.44 2.64

Field Bulk Density (g/cc) 1.65 1.79

Field Dry Density (g/cc) 1.49 1.63

Plastic Limit 27% Non-plastic

Porosity 0.34 0.38

Classification Silty

Clay

Poorly

Graded

Silty Sand Table 2 Geotechnical parameters of the soils adopted for this study [8,9]

Property (RS) (PYS)

Effective friction angle, φ' 31⁰ 38.5⁰

Effective cohesion, c' 10 kPa 0 kPa

Friction angle related to

matric suction, φb

16.7⁰ 7.5⁰

Permeability, ks (m/s) 1.86×10-6

1.21×10-5

The reported soil water characteristic curves

(SWCC) for both types of soils are presented in

Fig. 1. The unsaturated hydraulic conductivity

curve (UHCC) is derived empirically by

integrating along the entire curve of the volumetric

water content function (SWCC) [23] and

programmed within the GeoStudio Software Suite


[24]. Figure 2 presents the unsaturated hydraulic

conductivity curve derived for both type of soils.

Fig. 1 Soil water characteristic curves for the two

types of soil [8,9]

Fig. 2 Unsaturated hydraulic conductivity curves

for the two types of soil

PARAMETRIC STUDY

Methodology

The parametric study involves two parts. The first

part is transient seepage analysis to investigate the

infiltration mechanism under different rate of

infiltration and the simultaneous reduction in the

matric suction. The second part involves a slope

stability analysis applying limit equilibrium

method to determine the degradation of the

stability condition of the slope with time.

The infiltration is modeled using the seepage

analysis module SEEP/W of the commercially

available software suite GeoStudio [24]. The

coefficient of permeability is a non–linear function

of the matric suction (Fig. 3) within the soil under

unsaturated condition. SEEP/W applies finite

element method to solve the governing differential

equation describing the flow through soil, which in

this case is a modified form of the Richard’s

equation and is of the following form.

2x y w w

h h hk k q m

x x y y t

(1)

where mw2 is the coefficient of volumetric water

change with respect to a change in matric suction

and is equal to the slope of the SWCC at that

particular suction value, γw is the unit weight of

water and h is the hydraulic head. For efficient

solution of this problem, the SWCC, UHCC, the

unit boundary flux (q) on the surface of slope, and

the initial hydraulic head at all nodes of the mesh

needs to be defined before solving the model.

Two slopes of height 30 m with an inclination of

45⁰ (1H:1V) (Fig. 3) composed of homogenous and

isotropic residual soil was assumed. One slope was

assigned the red silty clay (RS) properties and the

other was assigned the pale yellow silty sand

(PYS) properties.

Fig. 3 Slope Geometry used in this study

The idealized slope isolates the influence of

complex hydro-geological conditions on the

seepage analysis and enables to understand the

individual response of each type of soil to a

particular applied infiltration. The slope was

discretized with a finite element mesh of combined

4-noded quadrilateral elements and 3-noded

triangular elements with a fineness of 0.5 m.

Surface elements of 0.1 m thickness were applied

to define the ground surface of the slope. A time–

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step of 1 hour was found to be sufficient for

efficient solution of the problem.

Initial groundwater level and the initial pore–water

pressure distribution were defined by applying a

phreatic line and restricting the maximum suction

to a limit of 80 kPa (Fig. 4). The maximum suction

value is chosen to reflect the in-situ moisture

content typical to the above mentioned residual

soils within the study area.

Fig. 4 Initial pore pressure distribution

The infiltration rate is modeled as a unit flux

boundary (q) along the nodes at the ground surface.

SEEP/W calculates the hydraulic head at each node

based on the nodal boundary flux converted from

the applied unit boundary flux. In the case of

ponding, i.e., development of positive pore-

pressure occurring at a ground surface node, the

hydraulic head at those nodes are reset to the

elevation of that node and the flux is determined.

As such the excess flux is lost as runoff.

For the slope stability analyses, Morgenstern-Price

method of slices with a half–sine inter slice force

function was applied. Morgenstern-Price method

satisfies both moment as well as force equilibrium.

The pore–water pressures determined in the

seepage analysis by SEEP/W are used as input data

in the slope stability analysis. The SLOPE/W

program considers unsaturated shear strength

conditions by implementing the modification of the

Mohr–Coulomb material model [25,26,27] and is

expressed in the following form.

ba a wf f ff

c' u tan ' u u tan (2)

where c' is the effective cohesion of the soil, σf is

the normal stress on the failure plain, ua is pore-air

pressure, uw is pore-water pressure, φ' is the

effective friction angle of the soil and φb is the

angle defining the increase in strength with

increase in matric suction. The parameter φb varies

with the degree of saturation. φb is equal to the

effective friction angle within the capillary zone

where the soil is saturated, but the pore-water

pressure is still negative; φb decreases as the soil

becomes unsaturated. Similar behavior is reported

for soils of the Guwahati hillslope regions [8,9].

However, as SLOPE/W is programmed to input Φb

as a constant value, the parameter is treated as a

constant and the adopted value is given in Table 2.

Five different rates of infiltration consistent to

storm events prevalent in this region vis. 50

mm/day, 100 mm/day, 150 mm/day, 200 mm/day

and 250 mm/day have been considered and applied

for duration of 5 days. The factor of safety of the

slopes are evaluated at an interval of 6 hours and

plotted against time.

Fig. 5(a) Variation of factor of safety with time for

the slope composed of red silty clay (RS)

Results

Figure 5 (a) & (b) gives the degradation of the

factor of safety of the slope composed of the silty


clay (RS) and the silty sand (PYS) respectively.

The most prominent observation that can be made

from figures is that slope stability analysis

applying conventional soil mechanics deliberately

ignoring soil suction gives an unrealistic estimate

of the stability condition and thus fails completely

to give an analytical description of the rainfall

induced slope failure mechanism. Comparing both

the figures, it can be understood that matric suction

and the cohesion component plays a significant

role in providing a much greater stability to the

slope composed of the silty clay (RS).

Fig. 5(b) Variation of factor of safety with time for

the slope composed of pale yellow silty sand (PYS)

Even after intense infiltration of 250 mm/day

applied for duration of 5 days, the slope composed

of silty clay (RS) is still stable, though very

marginally. On the other hand, such infiltration

caused the slope composed of the silty sand (PYS)

to undergo failure within duration of 1 day and 6

hours. Moreover, it is to be noted that the silty clay

(RS) has a much higher suction value at similar

volumetric water content range. This renders the

slope composed of the silty clay (RS) a much

greater stability. Figure 6 (a) and (b) gives a

graphical representation of the pore pressure

scenario across the entire slope. A gradual

development of pore pressure can be observed

within the slope composed of silty clay (RS). For

the silty sand (PYS) a distinct zone of wetting can

be observed.

Fig. 6(a) Pore Pressures (kPa) developed within

the slope composed of Red Silty Clay (RS) due to

an infiltration of 200 mm/day for a duration of 3

days

Fig. 6(b) Pore Pressures (kPa) developed within

the slope composed of Pale Yellow Silty Sand

(PYS) due to an infiltration of 200 mm/day for a

duration of 3 days

Figure 7 (a) and (b) gives the Factor of Safety for

the corresponding slopes at that particular time

step. Effect of the cohesive component of the silty

clay (RS) on the shape of the critical slip surface

can be easily identified (Fig. 7a). A circular and

moderately deep critical surface is observed,

however the factor of safety is still sufficient

enough to prevent failure of the slope. For the

slope composed of silty sand (PYS), the factor of

safety dips just below 1 indicating slippage. The

shape and depth of the critical slip surface indicates

a shallow translational slide which can be expected

considering the shear strength properties (Table 2)

of the particular type of soil. A close observation of

Figure 7(b) along with Figure 6(b) gives a clear

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picture of the failure occurring within the wetting

zone.

Fig. 7(a) Factor of Safety of the slope composed of

Red Silty Clay (RS) after an infiltration of 200

mm/day for duration of 3 days

Fig. 7(b) Factor of Safety of the slope composed of

Pale Yellow Silty Sand (PYS) after an infiltration

of 200 mm/day for duration of 3 days

Following the fact that the slope composed of the

silty sand (PYS) had undergone failure, the pore

pressures developed at the moment of the failure

are plotted in Fig. 8. The total applied cumulative

infiltration required to initiate failure was

calculated and plotted against rate of applied

infiltration in Fig. 9.

A linear relation was observed between rate of

applied infiltration and total cumulative rainfall

required to initiate failure (Fig. 10). This follows

from the fact that with decreasing rate of applied

infiltration, more amount rain water can infiltrate

into the slope minimizing the runoff.

Fig. 8 Pore Pressure within the slope composed of

Pale Yellow Silty Sand (PYS) at failure

Fig. 9 Total cumulative Rainfall required for

initiating slipping within the slope composed of

Pale Yellow Silty Sand (PYS) against the rate of

applied infiltration

Actual rainfall data was then input into the

simulation to assess the response of the model to

rainfall infiltration. The rainfall data used as input

is obtained from the Tropical Rainfall Measuring

Mission (TRMM) 3-hourly rainfall estimate (3B42

V7) data set for the Guwahati city location. The

time series rainfall data for duration of 84 hours (3


days and 12 hours) from afternoon of 4th

October

to the midnight of 7th

October, 2004, which has

been used in the analysis is obtained from Goddard

Earth Sciences Data and Information Services

Center (GES DISC) maintained web portal

Giovanni (http://disc.sci.gsfc.nasa.gov/giovanni).

Figure 10 gives the rainfall intensity versus time in

hours, used in the simulation.

Fig. 10 Rainfall storm event history (afternoon of

4th October to the midnight of 7th October, 2004)

Fig. 11 Factor of Safety vs. Time for slope

composed of Red Silty Clay (RS) and Pale Yellow

Silty Sand (PYS) for actual rainfall infiltration

The factor of safety of the slopes are then

calculated at intervals of 2 hours and plotted

against time. It can observe in the Fig. 11 that the

slope composed of the silty sand (PYS) is in near

failure condition at around 76 hours and undergoes

failure by 80 hours. The analysis shows that the

stability condition of the slopes can be well

predicted for actual rainfall condition with the

application of such simulation techniques. Such an

analysis can serve as basis for prediction of rain-

triggered landslides and develop early warning

where data on based on actual observation of

landslide occurrences and coupled rainfall storm

histories are not available.

CONCLUSIONS The most important and obvious conclusion that

can be drawn from the above analysis is that

suction within a soil layer plays a very significant

role in stabilizing a slope. Deliberately ignoring

suction in the stability analysis can not only give

an unrealistic result in terms of Factor of Safety but

also fail to explain how such steep natural slopes

can remain stable during the dry season.

Application of unsaturated soil mechanics helps in

understanding the mechanism that leads to the

failure of unsaturated soil slopes, providing a

quantified relationship between infiltration and the

destabilization of such soil slopes.

The other important conclusion that can be drawn

from this analysis is the fact that, saturation of the

soil layers need not be attained for failure to occur.

In the case of the slope composed of the silty sand

it can be observed that the pore water pressure was

still negative when failure occurred (Fig. 7). The

reddish silty clay (RS), due to its cohesion

component of shear strength and higher suction

values at comparable volumetric water content,

showed greater resilience than the slope composed

of pale yellow silty sand (PYS).

Coupling transient seepage analysis using the finite

element method in SEEP/W and then using the

output for slope stability analysis using the limit

equilibrium method in SLOPE/W, a predictive

model for rain-induced slope instability of natural

residual soil slopes can be developed to estimate

the degradation of stability condition ultimately

leading to failure. However the analysis results

depends greatly on the input parameters and thus

extensive field investigations, laboratory soil

testing, and rainfall data needs to be collected.

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The comparison shows that the variations in pore

water pressures distributed within the soil are

highly dependent on the soil water characteristics

and hydraulic conductivity function of the type of

soil. The results show that such a simulation of

saturated/unsaturated flow coupled with a limit

equilibrium slope stability model can provide

useful insight into development of pore pressure

scenario and rainfall induced slope failure.

The study suggests that slopes within the city of

Guwahati thus have the potential of undergoing

rainfall induced landsliding, highlighting the

observations made by previous researchers.

However, the potential will vary depending on the

type of soil and its response to infiltration.

This study cannot be regarded as a conclusive

effort to analyzing and understanding the

occurrence of rainfall induced landslide within the

Guwahati region. On the contrary, this study can be

considered as an effort to present the problem in

hand from an analytical point of view and laying

the emphasis on the physics of the problem.

REFERENCES

1. Kalita, U. C. (2001), A study of landslide

hazards in North Eastern India, Proceedings of

the Fifteenth International Conference on Soil

Mechanics and Geotechnical Engineering,

Istanbul, Turkey, 1-3, 1167-1170.

2. Sarma, A.K., and Bora, P.K. (1994), Influence

of Rainfall on Landslide, International

Conference on Landslides, Slope Stability and

the Safety of Infra-Structures, Malaysia.

3. GSI (2013), Geological Survey of India,

http://www.portal.gsi.gov.in, Landslide Home,

Post-disaster studies, accessed on 31 October

2013.

4. Selby, M. J. (1993), Hillslope Materials and

Processes, Oxford University Press Inc., New

York.

5. Glade, T. and Crozier, M. J. (2005), The nature

of landslide hazard impact, Landslide hazard

and risk, T. Glade, M. Anderson, M.J. Crozier,

(eds.), John Wiley and Sons, 43-74.

6. Glade, T. and Crozier, M. J. (2005), A review

of Scale Dependency in Landslide Hazard and

Risk Analysis, Landslide hazard and risk, T.

Glade, M. Anderson, M. J. Crozier, (eds.),.

John Wiley and Sons, 75-138.

7. Wesley, L. D. (2010), Geotechnical

Engineering in Residual Soils, John Wiley &

Sons Inc.

8. Das, U.K. and Saikia, B.D. (2010), Shear

Strength of Unsaturated Residual Soils of the

Hills in Guwahati, Proceedings of Indian

Geotechnical Conference, GEOtrendz, 679-682

9. Das, U.K. and Saikia, B.D. (2011), Evaluation

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Indian Geotechnical Conference (IGC-2010)igs/ldh/files/igc 2015 pune... · thus has the potential to be used in an early warning system against landslide hazard. The variation of