Loads on Braced Excavations in Soft Clay

Abstract

A parametric finite element study has been carried out to demonstrate the importance of clay strength and depth of clay layer on the earth pressures, strut loads, and bending moments for a strutted sheet pile wall in soft, essentially normally consolidated clay. The clay is modeled as nonlinear and anisotropic. The modeled excavation is 10 m deep. For a shear strength profile giving a close to failure condition the maximum bending moment is found to be 6 times larger than for a clay profile with 40% higher strength, and the maximum strut loads are up to twice as large. The maximum strut loads are significantly higher than those given by existing empirical design rules. Comparative analyses with an isotropic linear elastic-plastic soil model show relatively small differences in moments and strut loads. Comparisons against analyses with a beam-on-spring type finite element model show significant differences to the continuum FEM analyses. The main reason is that beam-on-spring models cannot capture the significant effect of arching on earth pressures, strut loads and bending moments.