Seismic Structural Considerations for the Stem and Base of Retaining Walls Subjected to Earthquake Ground Motions

ABSTRACT:

Cantilever retaining walls can respond externally to earthquake ground motions by sliding or by rotating, or internally by stem wall yielding. The type of response that will have the greatest impact on post-earthquake performance will likely depend on restraint conditions at the base of the wall. Walls founded on soil without an invert slab are most likely to dissipate the inertial energy imposed by earthquake ground motions by sliding. This may also be true for walls founded on fissured or fractured rock. Walls founded on soil or on fissured or fractured rock and prevented by an invert slab from moving laterally are more likely to tip (i.e., rotate) than to slide during a major earthquake event. Walls founded on competent rock without significant joints, faults, or bedding planes and prevented by a strong bond at
the rock-footing interface from either translating or rotating are likely to dissipate energy through plastic yielding in the stem wall. All three responses can leave the retaining wall in a permanently displaced condition.

The purpose of this report is to provide methodologies for conducting a performance-based earthquake evaluation related to plastic yielding in the stem wall. The methodologies include evaluation of brittle or force-controlled actions and the evaluation of ductile or deformation-controlled actions. The later evaluation provides estimates of permanent (residual) displacement for walls dominated by a stem wall yielding response.

Performance-based evaluation methodologies are demonstrated with respect to a wall designed to current Corps ultimate strength design criteria and with respect to an older retaining wall designed to working stress design criteria. Lap splice deficiencies related to older walls are discussed and performance-based evaluation techniques proposed.

At present the Corps computer program CWRotate is able to estimate permanent displacements associated with a sliding response and a rotational response. An enhancement is proposed to provide estimates of permanent (residual) displacement for walls dominated by stem wall yielding.

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