# Geotechnical Engineering Questions and Answers – Plastic Equilibrium in Soils : Active and Passive States

This set of Geotechnical Engineering Mcqs focuses on “Plastic Equilibrium in Soils : Active and Passive States”.

1. The theory of plasticity pertaining to soils is based on ___________
a) Mohr’s theory
b) Rankine’s method
c) Mohr-coulomb theory
d) None of the mentioned

Explanation: The theory of plasticity pertaining to soils is based on Mohr’s theory of rupture.

2. On designing retaining walls it is necessary to take care of __________ exerted by soil mass.
a) Erosion
b) Lateral pressure
c) Surcharge
d) Lateral stress

Explanation: In the designing of retaining walls; sheet piles or other earth-retaining structures, it is necessary to compute the lateral pressure exerted by the retained mass of soil.

3. The material retained or supported by the retaining structure is called __________
a) Surcharge
b) Support wall
c) Back fill
d) All of the mentioned

Explanation: The material retained or supported by the structure is called backfill which may have its top surface horizontal or inclined.

4. The coefficient of earth pressure when the soil is at equilibrium is ___________
a) σv /σh
b) σh /σv
c) σv × σh
d) σ1 / σ3

Explanation: When the soil is at elastic equilibrium(i.e. at rest) the ratio of horizontal to vertical stress is called the co-efficient of earth pressure of rest.
σh /σv = K0.

5. The computation of stress in plastic equilibrium is based on __________
a) Theory of plasticity
b) Mohr’s theory of rupture
c) Rankine’s theory
d) All of the mentioned

Explanation: The theory on which the computation of the stress in a state of plastic equilibrium is based is called the theory of plasticity.

6. The wedge-shaped portion of the backfill tending to move with the wall is called _______
a) Wedge fall
b) Active fall
c) Failure wedge
d) None of the mentioned

Explanation: During the active state, the wall moves away from backfill and a certain portion of the backfill in wedged-shaped tend to move which is called a failure wedge.

7. In active stress, the major principal stress σ1 acting on the wall will be in __________ plane.
a) Vertical
b) Horizontal
c) Inclined
d) Zero

Explanation: In an active state, the major principal stress σ1 is vertical and the minor principal stress σ3 is horizontal.

8. The plastic state of stress was proposed by ___________
a) Mohr
b) Rankine
c) Coulomb
d) Darcy

Explanation: The plastic state of stress when the failure is imminent was investigated by Rankine in 1860.

9. The position of the backfill lying above the horizontal plane at the top of wall is called _________
a) Active state
b) Plasticity
c) Surcharge
d) Slip lines

Explanation: The position of the backfill lying above a horizontal plane at the elevation of the top of a wall is called the surcharge, and its inclination to the horizontal is called surcharge angle β.

10. What will be the co-efficient of passive earth pressure, at a depth of 8m in cohesion less soil sand with an angle of internal friction of 30° when the water rises to the ground level?
a) 4
b) 5
c) 3
d) 1

Explanation: Given φ = 30°
Co-efficient of passive earth pressure, Kp = (1 + sin φ) / (1 – sin φ)
Kp = (1 + sin 30)/ (1 – sin 30°)
KP = 3.

Sanfoundry Global Education & Learning Series – Geotechnical Engineering.

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