Earth Pressure Theories
Rankine's Earth Pressure Theory
The Rankine's theory assumes that there is no wall friction (δ = 0), the ground and failure surfaces are straight planes, and that the resultant force acts parallel to the backfill slope.
In case of retaining structures, the earth retained may be filled up earth or natural soil. These backfill materials may exert certain lateral pressure on the wall. If the wall is rigid and does not move with the pressure exerted on the wall, the soil behind the wall will be in a state of elastic equilibrium. Consider the prismatic element E in the backfill at depth, z, as shown in Fig.
Earth Pressure at Rest
Rankine's Earth Pressure Against A Vertical Section With The Surface Horizontal With Cohesionless Backfill
Active earth pressure:
Rankine's active earth pressure in the cohesionless soil
Passive earth pressure:
Rankine's passive earth pressure in cohesionless soil
Rankine's active earth pressure with a sloping cohesionless backfill surface
As in the case of horizontal backfill, active case of plastic equilibrium can be developed in the backfill by rotating the wall about A away from the backfill. Let AC be the plane of rupture and the soil in the wedge ABC is in the state of plastic equilibrium.
Rankine's active earth pressures of cohesive soils with horizontal backfill on smooth vertical walls
Coulomb's Wedge Theory
Some Graphical solutions for lateral Earth Pressure are
- Culman's solution
- The trial wedge method
- The logarithmic spiral
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