1. GLE/CEE 330: Soil Mechanics Lateral Earth Pressure
Geological Engineering
University of Wisconsin-Madison

2. Learning Objectives Learn about key concepts:
Lateral earth pressure coefficients
At rest, active and passive earth pressure
Place in context of Mohr Circle analysis

3. Lateral Earth Pressure
(R.P. Weber) ??
(R.P. Weber)

4. Water Pressure and Soil Pressure
Consider hydrostatic condition
Consider “at-rest” (geostatic) condition
Anisotropic sx sz
Isotropic sz sx ≠
>

5. Earth Pressure Coefficient “At Rest”
K0 = Coefficient of Lateral Earth Pressure at Rest sx sz
For normally consolidated soil (Jaky, 1944):
For overconsolidated soil (Meyerhoff, 1976):
In general:

6. Calculate lateral total stress (sx) at z = 5 m if K0 = 0.5
(M. Budhu)

7. Active and Passive Limit Conditions
Ka = Coefficient of Active Earth Pressure
(Wall Moving Away from Backfill)
(small sx)
Active Failure Condition
movement
Active
Failure
Wedge
(45+f/2)
Kp = Coefficient of Passive Earth Pressure
(Wall Moving Toward Backfill)
(large sx)
Passive Failure Condition
movement
Passive
Failure
Wedge
(45 -f/2)

8. Consider Mohr’s Circles…
sx decreases until failure
movement
Active Failure
sx increases until failure
movement
Passive Failure

9. Rankine Active Failure Surface
Pole Point

10. Rankine Passive Failure Surface
Pole Point

11. Evolution of lateral stress with wall movement…
Stationary (at rest)
Movement away
from backfill
Movement toward
backfill
Passive Failure at Kp
Active Failure at Ka
Ka < K0< Kp

12. Essential Points 1) Coefficient of Lateral Earth Pressure at Rest
2) Active Earth Pressure Coefficient:
3) Passive Earth Pressure Coefficient:
4) Active slip planes at 45˚ + f’/2 to horizontal
5) Passive slip planes at 45˚ - f’/2 to horizontal
6) More wall movement (inward) required for passive failure than active (outward) failure