Tuesday, March 4, 2008

Retaining Walls - Questions

1. A retaining wall is designed for free-draining granular backfill. After several years of operation the weep holes become plugged and the water table rises to within 8 feet of the top of the wall.



a) What is the resultant force for the drained case?

b) What is the point of application of the drained case?

c) What is the resultant force for the plugged case?

d) What is the point of application of the resultant force for the plugged case?

2. Retaining Wall Design:
A reinforced concrete retaining wall is used to support a 15 ft cut in sandy soil. The backfill is level, but a surcharge of 450 lbf/ft^2 is present for a considerable distance behind the wall. Factor of safety of 1.4 against sliding and overturning are required. Customary and reasonable assumptions can be made. Passive pressure is disregarded. The need for a key must be established.


Soil drained specific weight = 125 lbf/ft^3
Angle of internal friction = 35°
Coefficient of friction against concrete = 0.45
Allowable soil pressure = 4800 lbf/ft^2
Frost line = 3.5 ft below grade


a) What is the minimum stem height?


For b-j, assume a base length B of 12 ft and a base thickness d = 2 ft. A stem thickness at base of 2 ft. And a stem thickness at top of 1.5 ft. A stem height above base of 19 ft. And a heel extension (past back of stem) = 7 ft.


b) What thickness of backfill is equivalent to the surcharge?
c) What is the horizontal reaction due to the surcharge?
d) What is the active soil resultant?
e) What is the total overturning moment, taken about the toe, per foot of wall?
f) What is the factor of safety against overturning?
g) What is the maximum vertical pressure at the toe?
h) What is the minimum vertical pressure at the heel?
i) What is the factor of safety against sliding without a key?
j) What is the factor of safety against sliding if a key of 2 ft wide and 1 ft deep is used?

1 comment:

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