UNIT V. The active earth pressure occurs when the wall moves away from the earth and reduces pressure.

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1 UNIT V 1. Define Active Earth pressure. The active earth pressure occurs when the wall moves away from the earth and reduces pressure. 2. Define Passive Earth pressure. The passive earth pressure occurs when the wall moves towards from the earth and increases pressure. 3. Enumerate the assumptions made in Rankine s theory. (M/J 08) o semi infinite soil o cohesion-less backfill o homogenous soil o The top surface is a plane which may be inclined or horizontal. 4. Enumerate the assumptions made in Coulomb s Wedge theory. (M/J 08) o The backfill is dry, cohesionless, isotropic, and homogenous. o The slip surface is plane which passes through the head of the wall. 5. Distinguish Coloumb s wedge theory from Rankine s theory? (M/J14) Rankine considered a soil particle at plastic equilibrium but Coulomb considered the whole soil mass. 6. Write down any two assumptions of Rankine s theory? o semi infinite soil o cohesion-less backfill 7. What are the stability conditions should be checked for the retaining wall [N/D-8] Over turning Sliding Bearing capacity failure 8. Why the passive earth pressure is not normally considered in the design? The passive earth pressure occurs when a wall or plane moves towards earth. This will create additional pressure where as in the case of active pressure, wall moves away from earth and therefore there is a reduction in pressure on the wall. That is why passive earth pressure is not used in the design. 9. Retaining walls are usually designed for active earth pressure. Why? A retaining structure is required to provide lateral support to the soil mass behind it. The tendency of the backfill is to push the retaining wall away from it such that the soil stretches horizontally. This state is active and hence the retaining walls are designed for active earth pressure. 10. Define angle of repose? (M/J 08) Maximum natural slope at which the soil particles may rest due to their internal friction, if left unsupported for sufficient length of time 11. Define theory of plasticity? The theory on which the condition of the stress in a state of a plastic equilibrium is called as theory of plasticity 12. How to prevent land sliding? Sheet piles, retaining wall may be used to prevent the land sliding. 13. What is surcharge?

2 The position of backfill lying above a horizontal plane at the elevation of the top of a wall is called the surcharge. 14. Define surcharge angle [N/D-15] The angle of repose, or critical angle of repose, of a granular material is the steepest angle of descent or dip relative to the horizontal plane to which a material can be piled without slumping. At this angle, the material on the slope face is on the verge of sliding. The angle of repose can range from 0 to What force is acting on retaining wall? [N/D-15] Vertical forces: Acting downwards: Self weight of the retaining wall ; Weight of soil above heel slab. Acting upwards: Force due to soil pressure underneath the base slab. 8. If backfill is sloping; ὰ 16. Draw the variation of lateral earth pressure with wall movement. [M/J-16]

3 17. Draw the force polygon for lateral active earth pressure on wall retaining cohesion less soil according to Coulomb's wedge theory. [M/J-16] 18. Write any two assumptions in Coulomb's wedge theory? [N/D-16]

4 19. Distinguish Coulomb's wedge theory from Rankine's theory (N/D-16)

5 2. Discuss in detail about the Rankines theory for the following cases of cohesion soil and cohesive soil. (i) Submerged backfill ii) Back fill with sloping surface [N/D-15] 3.(a) Explain Culmann's graphical method for determining active lateral earth pressure on rigid retaining wall.[ M/J-16]

7 4. (b) Explain Rankine's theory for active and passive earth pressures on rigid wall cohesive soil. Consider both presence and absence of tension crack for active case. [M/J-16]

10 2. (b) Explain the Rankine's theory for various backfillconditions to calculate active state earth pressure. (N/D-16)

FOUNDATION ENGINEERING UNIT V

FOUNDATION ENGINEERING UNIT V RETAINING WALLS Plastic equilibrium in soils active and passive states Rankine s theory cohesion less and cohesive soil - Coloumb s wedge theory condition for critical failure