Coulomb’s concept states that the entire lateral earth strain is the same as the response exerted via way of means of the keeping wall while the wedge of soil has a tendency to slip and acts at an attitude eight with the ordinary to the again of the wall.
- The backfill is dry, cohesionless, isotropic, Backfill can be inclined.
- There could be friction among the wall and the soil.
- Failure aircraft is thought to be an aircraft surface (however in reality curved), Sliding wedge is thought to be a rigid-body.
- Active earth pressure decreases while considering wall friction and passive earth pressure increases by considering wall friction.
- The position and line of action of earth pressure will be known in advance. The line of action of earth pressure will act at 1/3 depth from the bottom and will be inclined at an angle from the normal to the wall.
- δ is approximately taken as
- The earth’s pressure is assumed to be the reaction given by the wall.
- For coulomb theory, the static equilibrium not satisfied in nature, i.e instead the force triangle (Fig.17), all the forces must pass through one point.
- The trial edge is selected at some angle „θ „.
- The trial edge will be having forces W, R, P as shown in Fig. the direction and magnitude of all the forces is known.
- By assuming various trial wedges at a different angle the value of „P‟ will be calculated.
- For Active Earth Pressure, P is the highest value obtained for various trial wedges.
- For Passive Earth Pressure, P is the minimum value.
- Rankine Earth Pressure theory overestimates the active earth pressure and underestimates the passive earth pressure.
- On compacting the soil, active earth pressure decreases while passive earth pressure increases.
- If the wall is smooth,
- When =0 than Column and Rankine result matches i.e wall must be vertical, the soil is cohesionless and backfill angle is 0
- For the masonry gravity wall, the Coulomb wedge theory is preferred while designing cantilever and counterfeit retaining wall, Rankine theory is preferred.
- For Abutment, the soil is taken as rest, for assessing the stability of the soil, while active pressure is considered when assessing the adequacy of a structural element of abutment and passive pressure is considered when integral abutment under thermal effect.
- Weep holes are provided at the back of the retaining wall to reduce the build-up of hydrostatic pressure.
