Numerical Modeling of a Crib-wall Failure

The 2-D finite difference program FLAC was utilized to investigate the probable cause of failure of a crib wall at Hebrew Union College in Los Angeles. Shortly after reaching its final height of 45 feet, cracking/crushing of the precast-concrete elements had been observed, and the crib wall was lowered to 35 feet. In spite of this design change, however, a portion of the wall later collapsed following prolonged rainfalls in March of 1992. In analyzing the construction stages and subsequent wall failure, a simple Mohr-Coulomb constitutive model was coupled with seepage analysis to simulate the effect of rainwater infiltration. Two distinct case histories were analyzed. The first case involved wall construction through completion, when localized crushing of crib-wall elements occurred even before the rainy season. The second case simulated a prolonged period of rainfall during which the wall collapsed. It was found that the low-permeability backfill material allowed the buildup of pore pressures which triggered the collapse of the wall. However, it was also concluded that neither the initial cracking/crushing nor the subsequent wall collapse would have occurred had the stacked crib-wall elements possessed the concrete compressive strength specified in the design