Question

Please explain why high pore-water pressures reduce friction along the base of a retaining wall footing.

Answer 1

Retaining wall is constructed or designed to hold the wedge of soil or from the lateral earth pressure of soil. The pressure which comes from the groundwater below the retaining wall footing is called pore water pressure. Due to pore water ( as water acts as a viscous liquid) the soil beneath the footing reaches its saturation level and molecular force between the soil particles and the base of the footing is reduced, as a result angle of internal friction is reduced and the friction along the base of footing reduce. In this way, pore water pressure refuces the friction.