Case Study: 3D MOBILIZED STRENGTH OF COMPACTED FILL

Abstract

Water infiltration can cause softening of compacted structural fill and a reduction of the shear strength from the peak compacted strength to the fully softened strength (FSS) with an accompanying reduction in drained factor of safety (FoS). This paper presents 2D and 3D stability analyses of a compacted fill slope failure that occurred six years after construction due to water leaking from a connection between the main and lateral water pipes in the water supply system. The compacted fill material primarily consists of high plasticity fine-grained soil. The 3D FoS at the end of construction is 2.44 using the peak compacted strength envelope. However, the 3D FoS is close to unity (1.0) when the FSS is assigned to the compacted fill material with the appropriate piezometric surface, which means the 2H:1V compacted fill slope softened to the FSS within six years. This case is an interesting FSS case because the failure surface is 4 m deep and semi-circular, which differs from infiltration cases that exhibit a shallower and more planar surface.