Friday, October 7, 2016

Lateral Thrust on a Wall at rest against a Soil Backfill


A lateral thrust is applied by the soil backfilled behind a wall at rest, this thrust is known as the lateral thrust at rest. Walls which are restricted against any movements or moment come under this category. Example can be a basement wall, which is topped with a RCC slab, and therefore restricts its movement. The amount of thrust on the wall depends upon the properties of the soil.

Density of the soil, angle of friction, degree of the consolidation and the level of the water table are the major factors which govern the magnitude of the lateral thrust.

Example: A 10 m high basement wall, behind which is filled a soil with density 19.7 kN/m3, c=0,
OCR= 2, πœ™ = 35°, π›Ύπ‘‘ = 19.7 kN/m3. Find the lateral thrust and its location from base.


Fig. Lateral Thrust diagram for wall at rest. 
πΎπ‘œ = 1 - sinπœ™ = 1 - sin35° = 0.426

πΎπ‘œ(overconsolidated) = πΎπ‘œ(normally consolidated )√OCR
πΎπ‘œ(overconsolidated) = 0.426√2 = 0.602

At any depth z
    𝜎′𝑣  = z.𝛾𝑑,   [pore water pressure u= 0)
    𝜎′β„Ž = πΎπ‘œ*𝜎′𝑣
Depth,  z= 0
    𝜎′𝑣  = 0,  πœŽ′β„Ž = 0
Depth,  z= H=10 m
     πœŽ′𝑣  = 10*19.7 = 197 kN/m2,
     πœŽ′β„Ž = 0.602*197 = 118.594 kN/m2

Lateral Thrust = Area of the lateral stress diagram.  = 1/2 (10*118.59) = 592.97 kN

Lateral thrust acts at the centroid of the lateral stress diagram, i.e. at a height of H/3 from base.
H/3 = 10/3 = 3.333 m from base.