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Civil - Soil Mechanics -Slope Stability

Important Question And Answer: Slope Stability

   Posted On :  11.07.2016 11:42 pm

Civil - Soil Mechanics -Slope Stability

Important Question And Answer:  Slope Stability


1. What are the factors leading to the failure of slopes?


The factors leading to the failure of slope may be classified in to two categories.


a)     The factors which cause an increase in the shear stresses loads, seepage pressure.


b)    The factors which cause a decrease in the shear stresses. This is due to increase in water content, increase in pore water, weathering. or

The failure of slope occurs due to

i.                   The action of gravitational forces


ii.                 Seepage forces within the soil


iii.              Excavation or undercutting of its foot, or due to gradual disintegration of the soil.

2. What is a land slide?


Failure involving downward or outward movement of portion of the soil is the case of natural slope is known as land slide.


3. What do you know about Infinite slope?


A Infinite slope is very large in extent and is theoretically infinite and the properties of the soil will be same at identical points.


4. What do you mean by Finite Slope?


A Finite slope is limited in extent and t be same at identical depths. So that the slip surface may be curved.


5. What are the two basic types of slope failure -Define.

(1)                Slope failure


(2)                Base failure


(1) Slope failure:


If the failure occurs along a surface of sliding that intersects the slope at or above its toe, the slide is known as slope failure.


(2) Base failure:


If the failure occurs along a surface that is some distance below the toe of a slope is known as base failure.

6. What are the two types of slope failure?

1)Face failure


2)Toe failure


1) Face failure


If the failure occurs above the toe, then the failure is said to be face failure.


2) Toe failure


If the failure occurs through the toe, then the failure is said to be Toe failure.



7. Define Depth factor.


The ratio of total depth (H+D) to depth H is called depth factor (Df).


(1)  For toe failure, Df = 1


(2)   For base failure, Df > 1


8. What are the types of slip surface in a Finite slope.


1. Planar failure surface


2. Circular failure surface


3. Non circular failure surface


9. What are the different methods used for analysis of finite slope.


1. Culmann's  method  of  planar  failure  surfa


2. Swedish circle method (slip circle method)

3. Friction circle method


4. Bishop's  method



10.              What do you mean by planar failure?


Planar failure surface may commonly occur in a soil deposit or embankment with a specific plane of weakness. It is common in stratified deposit and the failure plane is 11el to the strata.





11.              Where does a Noncircular (composite) slip surface occur in a homogenous dam?


1. Foundation of infinite depth


2. Rigid boundary planes of maximum or zero shear.


1.Presence of relatively stronger or weaker layes. Presence of a soft layer in foundation


2. Use of different type of soil or rack in the dam section with varying strength and pore pressure condition.


3. Use of drainage blankets to facilitate dissipation of pore pressure.




13.              Write down the assumptions made in the analysis of slope?


1. The stress is assumed to be two dimensional.


2.  Coulomb equation for shear strength is applicable and parameters and

?  are  known.


3. Seepage pressure was estimated from the assumed seepage conditions and water levels.


4.  The conditions of plastic failure are assumed to be satisfied along the critical surface.




14. What are the three forces acting in circular failure while analysis through friction circle method?


1. Weight (w) of the sliding wedge

2. Cohesive force (C) developed along the slip surface


3. Reaction (R) on the slip surface


15.              What do you mean by slide?


The failure of a mass of soil located beneath a slope a called a slide.


16. Why does a slope be analysed?


The failure of slope is analysed thoroughly since their failure may lead to loss of human life as well as colossal economic loss.


17. Define Stability number?


The force causing instability is the weight of the wedge which I equal to unit


weight ? and the areaIproportionalof to thesquarewedgeofthe which height H. It is a dimensionless quantity.

Sn=C/FC ?H


Sn =Stability number


Fc -Factor of safety


??unit weight


H -Height of the scope


18.              What are the Factor of safety used in stability Analysis of slopes?


1. Factor of safety with respect to cohesion assuming to be fully mobilized.


2. Factor of safety with respect to friction assuming to be fully mobilized.


3. Factor of safety with respect to shear strength


4. Factor of safety with respect to height.


19.              Write down the formula for calculating factor of safety with respect t cohesion?




Fc = cm (assuming friction to be fully mobilisede)

Fc -Factpr pf safetu wotj res[ect tp cpjesopm


C -ultimate cohesion


cm -mobilized cohesion





Tags : Civil - Soil Mechanics -Slope Stability
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