Dynamic Lateral Pressures Due to Saturated Backfills on Rigid Walls

One‐directional (horizontal) shaking‐table experiments were conducted on one sandy and two cohesive saturated backfills to investigate the dynamic water and total lateral pressures against rigid nonyielding walls during earthquakes. It was found that the dynamic water pressure against the wall is generated due to two different sources. The first source is Westergaard‐type, which is due to the flow of free water in nondeformable backfill soil skeleton and the second is due to the deformability of backfill soil skeleton under undrained conditions. For highly permeable backfill soils, the first source dominates in the generation of pore pressure and the second source dominates for cohesive backfills. The magnitude of the first type of dynamic water pressure is expressed as a function of the parameter $2\pi n;{\gamma }_w{H^2}_w/E_w\mathrm{kT}$, where $n$ is the porosity of soil, ${\gamma }_w$ is the unit weight of water, $H_w$ is the depth of water table to the impermeable base in the backfill, $E_w$ is the coefficient of compressibility of water, $k$ is the coefficient of permeability of backfill soil, and $T$ the period of vibration. The water pressure distribution is a shape of the Westergaard solution. The distribution of the second type is different from the Westergaard‐type with a peak value at an upper section of the backfill depth and zero at the bottom. The dynamic water pressure resultants of this type for cohesive backfills are nearly as much as the value of Westergaard's but is applied at approximately 0.6H from the bottom of the backfill. The dynamic total pressure resultants for cohesive backfills are nearly twice Westergaard's dynamic water pressure resultant and also applied 0.6H from the bottom of the backfill.