Finite Element Analyses of Lock and Dam 26 Cofferdam

Abstract

Replacement of the old Lock and Dam 26 on the Mississippi River involves construction of one of the largest systems of cellular cofferdams ever built. Preliminary analyses using conventional theories led to sometimes contradictory recommendations about the cofferdam design. To help resolve outstanding issues, instrumentation was placed on the first‐stage cofferdam, and finite element procedures were developed for analysis of the cofferdam. Three different two‐dimensional finite element procedures were generated, including axisymmetric, vertical slice, and generalized plane‐strain models. The alternative approaches allowed prediction of cofferdam response for the most important design conditions and at the critical locations. In all models, allowances were made for nonlinear soil response, slippage on the sheet‐pile‐soil interfaces, staged construction simulation and seepage effects where appropriate. Further, a means was provided to accommodate the effect of sheet‐pile interlock yielding, which led to an orthotropic response of the cellular cofferdam. Predicted behavior from the finite element models was found to be consistent with observed trends. The models appear to have considerable potential for use in future designs.