This set of Design of RC Structures Multiple Choice Questions & Answers (MCQs) focuses on “Retaining Walls”.
1. Retaining wall is for maintaining the ground surfaces at different elevations on either side of it.
a) True
b) False
View Answer
Explanation: A retaining wall or retaining structure is for maintaining the ground surfaces at different elevations on either side of it. Whenever the embankments are constructed, retaining walls are necessary. In the design, it is necessary to compute the lateral earth pressure exerted by soil mass.
2. Which of the following does not require construction of retaining walls?
a) Basements
b) Bridge walls
c) Bridge abutments
d) Footing of size 100 mm deep
View Answer
Explanation: A concrete footing is 100 mm deep by 300 mm wide for free structures. For retaining walls the footing should be 150 mm deep and 450 mm wide. Retaining walls are mandatory for buildings with basements. In bridge work the wing walls, abutments, etc. should be built as retaining walls. These resist the earth pressure along with superimposed loads.
3. Which of the following is the weight added above retaining walls?
a) Backfill
b) Surcharge
c) Superimposed loads
d) Earth pressure
View Answer
Explanation: The material that retaining wall support is backfill. The top surface of backfill can be horizontal or inclined. Position of backfill lying above the horizontal plane at the elevation of the top of a wall is surcharge. Angle of inclination of surcharge with horizontal is the surcharge angle.
4. What is the symbol used for surcharge angle?
a) α
b) β
c) Φ
d) γ
View Answer
Explanation: Surcharge is the vertical load imposed on retained soil that imposes a lateral force in addition to lateral earth pressure of retained soil. Angle of surcharge is the angle that material makes with the horizontal. This angle of inclination is (β).
5. Which of the following is the cheapest material for retaining walls?
a) Brick
b) Wood
c) Treated pine
d) Dry stones or boulders
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Explanation: Poured concrete is most used material for retaining walls. Brick made wall is strong and durable. The walls made of wood, dry stone and dry boulders are strong. Treated pine is the cheapest of all the options, but it will not last as long as other materials.
6. Which type of retaining walls develop no tension?
a) Gravity walls
b) Cantilever walls
c) Counterfort walls
d) Buttressed walls
View Answer
Explanation: In gravity retaining walls, the earth pressure which the backfill exerts, can be resisted by dead weight of the wall. The wall is of masonry or mass concrete. All stresses in the wall are low. These walls are so proportioned that no tension is there. Resultant of forces remains within the middle third of the base.
7. Which type of retaining wall can resist both the horizontal and vertical pressure?
a) Gravity walls
b) Cantilever walls
c) Counterfort walls
d) Buttressed walls
View Answer
Explanation: The cantilever walls can resist both the horizontal earth pressure and vertical pressures, by way of bending of various components acting as cantilevers. Most commonly used cantilevers retaining wall is the T – shaped wall.
8. A buttressed wall is a modification of the counterfort retaining wall.
a) True
b) False
View Answer
Explanation: A buttressed wall is a modification of the counterfort retaining wall. In this the counterforts are the buttresses, provided to the other side of the backfill. The buttresses reduce the clearance in front of the wall, so these are less commonly used.
9. What is the increment in lateral earth pressure when backfill carries surcharge of uniform intensity (w) per unit area?
a) Kaw
b) (1/4)Kaw
c) (1/2)Kaw
d) 2Kaw
View Answer
Explanation: When the backfill is horizontal carrying a surcharge of uniform intensity (w) per unit area, the vertical pressure will increase by (w). The increase in lateral pressure because of this will be (Kaw). The equation for lateral pressure at any depth (h) is given by:
pa = Kaγh+ Kaw.
Here w is the surcharge of unit weight per unit area.
10. The lateral pressure increment due to the surcharge is same at every point at the back of the wall.
a) True
b) False
View Answer
Explanation: The lateral pressure increment (Kaw) due to surcharge (w) is the same at every point at the back of the wall. It does not vary with height (h). Height of the fill (he) is equal to the uniform surcharge intensity given by:
Kaγhe = Kaw or he = w/γ.
11. What is the intensity of passive pressure at depth (h) with a uniform surcharge of (w) acting on the backfill?
a) 2Kp (γh + w)
b) Kp (γh + w)
c) Kp (γh)
d) Kp (2γh + w)
View Answer
Explanation: When a uniform surcharge of intensity (w) per unit area acts over the surface of backfill. The increment in the passive pressure is given by:
pp = Kp (γh + w)
Here Kp is coefficient of passive pressure.
Sanfoundry Global Education & Learning Series – Design of RC Structures
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