Practice Question: Resultant Force on a Gravity Wall
NCEES Civil PE Specification Soil Mechanics: Lateral earth pressure
Problem
For the given soil parameters, use lateral active earth pressure to determine the total resultant force acting on the retaining wall.
- Ignore friction between soil and wall
CORRECT 😃
INCORRECT 😟
% Students Correctly Answered:
70.8%
Solution
Answer: D) 5 Kips
According to Rankine theory the active earth pressure coefficient is as follows:
\[K_{a} = \frac{[1 - sin \phi ]}{[1 + sin \phi ]} = \frac{[1- sin 27 ]}{[1 + sin 27 ]} = 0.375\]
Stress at wall bottom:
\[= \gamma \times h \times K_{a} = 120 \times 15 \times 0.375 = 675\ PSF\]
Force acting on the wall:
\[=0.5 \times γ \times h^2 \times K_{a} = 0.5 \times 120 \times 15^2 \times 0.375 = 5062.5\ lb = 5.06\ kip\]
