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? **

*C*

*Fc
*=*
cm *(assuming friction to be fully mobilisede)

Fc
-Factpr pf safetu wotj res[ect tp cpjesopm

C
-ultimate cohesion

cm
-mobilized cohesion

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