Basic Theory of Earth Pressures

Question 1

Retaining walls

Answer 1

Support vertical soil masses that would otherwise fall due to lateral forces from excavation or filling
- Gravity walls
- Cantilever walls, designed for tension therefore have reinforcement
- Strong structures and anchors
- Tensile reinforced earth

Question 2

Available tools for analysis

Answer 2

-Empiricism: Using experience
-Limit equilibrium: Assumes a failure mechanism but has weak theoretical basis
-Stress field: Assumes domain is in failure and get boundary stresses from equilibrium
-Plasticity theorems: Upper bound uses work calculations on kinematically feasible failure mechanism while lower bound assumes failure in the domain of a system in static equilibrium
-Numerical solutions: Continuum solutions solve the entire problem that is moments, boundary F and soil stresses. Solutions limited by model, software and parameters used
-Simplified numerical approximations: Simplify the soil to 1D treating it a s a nonlinear spring

Question 3

Problems

Answer 3

-Earth pressures and WP
-Stability of structure @ a given depth
-Ground movements
-Support system
-Forces in struts and anchors

Question 4

Earth pressures at rest

Answer 4

-For flat ground
-Apply Jaky for NC, another equation for OC

Question 5

Rankines stress field

Answer 5

• Assumes infinitely deep smooth wall at K0 less than 1, therefore low
• Active is the side behind the wall, decreeing sigma_h’
• Passive is the side in front of the wall therefore increasing sigma_h’
• Note sigma1’ is greater than sigma3’ for mohrs circle

Question 6

Earth pressure coeff. in cohesionless soil

Answer 6

Cohesionless therefore c’ = 0
-Kp>K0>Ka
-Max obliquity is with reference to max(tau/sigma_n’)
* Angle from the pole (sigma_h’) to lines that intersect the failure surface, measured from horizontal to certical
*Rupture surfaces usually // to thee directions