Mitigating Lateral Spreading Forces on Large Foundations Using Ground Deflection Walls

Deflection walls were considered for mitigating lateral spreading-induced bending moments on large-dimension foundations. The efficacy of the walls was tested using dynamic centrifuge testing of a large-dimension rectangular foundation (caisson) with and without an upslope ground deflection wall. The ground deflection walls were modeled as buttressed sheet pile walls and were intended to deflect the laterally spreading ground around the caisson and reduce the pressure transmitted to the caisson. Three wall shapes (chevron, arch, and truncated chevron) were tested in all-sand profiles and profiles with a clay cap underlain by sand. In contrast to the unprotected caisson tests, the deflection walls successfully redirected the laterally spreading sand-only profiles around the caisson and minimized passive wedge development upslope of the caisson. Maximum lateral pressures measured on the upslope face of protected caissons ranged from at-rest pressures to the total vertical stress and were about 30%-50% lower than those measured against unprotected caissons. Based on these results, the proposed buttressed sheet pile walls may be suitable to mitigate lateral spreading forces on existing foundations. These results also suggest that newly constructed large foundations or pile groups may be arranged in a diamond or circular pattern to better mitigate potential lateral spreading earth pressures.