Geotechnical Engineering Questions and Answers – Coulomb’s Wedge Theory

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This set of Geotechnical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Coulomb’s Wedge Theory”.

1. The wedge theory of earth pressure is based on the concept of _________
a) Active earth pressure
b) Sliding wedge
c) Wall friction
d) All of the mentioned

Explanation: The wedge theory of earth pressure is based on the concept of a sliding wedge which is torn off from the rest of the backfill on a movement of the wall.

2. Which of the following is a basic assumption of the wedge theory?
a) The slip surface is plane
b) The backfill is dry
c) The backfill is homogeneous
d) All of the mentioned

Explanation: Based on the assumptions of the wedge theory:
i. The backfill is dry, cohesion less, homogeneous, isotropic, and elastically undeformable.
ii. The slip surface is a plane which passes through the heel of the wall
iii. The sliding wedge itself acts as a rigid body.

3. The force acting on a wedge of soil are ____________
a) Frictional force
b) Weight of the wedge and Active thrust
c) None of the mentioned
d) All of the mentioned

Explanation: According to wedge theory, the forces acting on a wedge of soil are its weight W, the reaction R along the plane of sliding and the active thrust against the retaining wall.
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4. The active lateral pressure of intact saturated clays is calculated by assuming __________
a) φ=0 and φc=0
b) φ=90
c) None of the mentioned
d) All of the mentioned

Explanation: The active lateral pressure of intact saturated clays for temporary works or immediately after construction of a retaining wall is calculated by assuming φ=φc=0.

5. The forces acting on the trial wedge which is used for finding Rankine’s active earth pressure is __________
a) Weight W of the wedge
b) Resultant force
c) Resultant reaction between wedge and sol
d) All of the mentioned

Explanation: The three forces acting on a trial wedge are: i) the resultant force that exist between the free body and the wall ii) the weight W of the wedge iii) the resultant reaction between the wedges and the rest of the soil along the surface.

6. The Rankine’s active earth pressure can also be found out by method of _____________
a) Trial wedges
b) Graphical method
c) Sliding wedge
d) Theoretical calculation

Explanation: The Rankine’s active earth pressure (assuming the wall to be smooth) can be found out by method of trial wedges.

7. Based on the assumptions of the wedge theory, pressure distribution is assumed to be __________
a) Planar
b) Hydrostatic
c) Equal
d) Distributed

Explanation: The assumption is based on that, the total pressure distribution is hydrostatic,i.e., triangular

8. In Coulomb’s wedge theory, the angle λ is referred as ___________
a) Angle of wall friction
b) Surcharge angle
c) Critical slip angle
d) None of the mentioned

Explanation: In wedge theory, the angle between the slip plane and the ground is called the critical angle λ.

9. The φ-line in wedge theory can also be called as __________
a) Surcharge line
b) Natural slope line and Repose line
c) None of the mentioned
d) All of the mentioned

Explanation: The φ-line shows a plane inclined at an angle φ to the horizontal at which the soil is expected to stay in the absence of any lateral support. The line therefore is called the natural slope line or repose line.

10. In coulomb’s wedge theory, the criterion for maximum active pressure is present at ___________
a) Slip-plane
b) Repose line
c) Surcharge line
d) Ground line

Explanation: In 1971, Professor Rebhann presented that the criterion for maximum active pressure is present at the slip–plane of the assumed triangle.

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