RETAINING WALL STABILITY CALCULATION SAMPLE BASICS AND TUTORIALS

RETAINING WALL DESIGN EXAMPLE - STABILITY TUTORIALS
How To Design Retaining Wall


EXAMPLE

Determine the factor of safety (FS) against sliding and overturning of the concrete retaining wall in Figure. The concrete weighs 150 lb/ft3 (23.56 kN/m3, the earth weighs 100 lb/ft3 (15.71 kN/m3), the coefficient of friction is 0.6, and the coefficient of active earth pressure is 0.333.



Calculation Procedure:



1. Compute the vertical loads on the wall

Select a 1-ft (304.8-mm) length of wall as typical of the entire structure. The horizontal pressure of the confined soil varies linearly with the depth and is represented by the triangle BGF in Fig. 10

Resolve the wall into the elements AECD and AEB; pass the vertical plane BF through the soil. Calculate the vertical loads, and locate their resultants with respect to the toe C. Thus:

W1 = 15(I)(ISO) = 2250 Ib (10,008N);
W2 = 0.5(15)(5)(150) = 5625;
W3 =0.5(15XS)(IOO) = 3750

Then ^W = 11,625 Ib (51,708 N). Also, Jc1 = 0.5 ft; X2= 1 + 0333(5) = 2.67 ft (0.81 m); Jc3 = 1 + 0.667(5)-433 ft (1.32m).

2. Compute the resultant horizontal soil thrust

Compute the resultant horizontal thrust T Ib of the soil by  applying the coefficient of active earth pressure.

Determine the location of T. Thus BG = 0.333(1S)(IOO) = 500 Ib/lin ft (7295 N/m); T = 0.5(15)(500) = 3750 Ib (16,680 N); y = 0.333(15) = 5 ft (1.5m).

3. Compute the maximum frictional force preventing sliding

The maximum frictional force Fm = where M = coefficient of friction. Or Fm = 0.6(11,625) - 6975 Ib (31,024.8N).

4. Determine the factor of safety against sliding 

The factor of safety against sliding is FSS = FJT = 6975/3750 = 1.86.

5. Compute the moment of the overturning and stabilizing forces

Taking moments with respect to C, we find the overturning moment = 3750(5)
= 18,750 lb-ft (25,406.3 N-m).

Likewise, the stabilizing moment = 2250(0.5) + 5625(2.67) + 3750(4.33) = 32,375 lb-ft (43,868.1 N-m).

6. Compute the factor of safety against overturning

The factor of safely against overturning is FSO = stabilizing moment, lb-ft (N-m)/overturning moment. lb-ft (N-m) = 32,375/18,750 = 1.73.

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