Lateral Earth Pressure

Loads and Forces Acting on Retaining Wall There are various types of loads and forces acting on retaining wall, which are: Lateral earth pressure Surcharge loads Axial loads Wind on projecting stem Impact forces Seismic earth pressure Seismic wall self-weight forces

Surcharge loads acting on retaining wall are additional vertical loads that are used to the backfill soil above the top of the wall. It can be either dead loads for example sloping backfill above the wall height or live load which could result from highway or parking lot, paving or adjacent footing.

Effective stress (σ‘) Total Normal Stress (σ) Pore Water Pressure (u)

σ

σ

σ‘

Defined as soil stress which not influenced by water pressure in soil body.

sat

sat sub

• σ

Vertical pressure

Lateral pressure

σh/ σv

• 1) At-rest : Soils in nature have an in-situ state of stress. This "in-situ" state of stress is commonly referred to as "At-rest" conditions.

• If a natural surface is level and all stratigraphy is also level, then the "At-rest" state of stress can be described by two main stresses:

a) The vertical stress [σv](effective stress (σ’) and total stress (σ))

b) The horizontal stress[σH]

σv

σH

1)At – rest condition

K0 = σH/ σV

• All effective horizontal stresses are

• K0 = coefficient of lateral pressure.

• σ V = effective vertical stress

• For "At-rest" conditions, coefficient of lateral pressure is :

V …Lateral earth pressure is function of vertical stress

At – rest condition

• If a stiff gravity wall fully bears on bedrock, in such a condition a retaining wall will essentially feel the full "At-rest" driving soil pressures.

Soil element

σv = Ꝩz

2) Active earth pressure • Soil pressure that is trying to move the structure

Soil expands by an amount ΔH

3) Passive earth pressure

Soil compresses by an amount ΔH

p

+

-

+

p p

Refer notes and problems solved in class