Pile end-bearing capacity in crushable sands

The occurrence and formation of crushable soils is a widespread phenomenon. Warm tropical seas give rise to deep deposits of biogenic skeletal sediments in coastal shelf areas, or exposed granitic intrusions are subjected to deep weathering resulting in decomposition. The end-bearing capacity of piles in crushable soils is important for the design of foundations in these diverse soils, but the analysis of foundations in these soils is problematic due to their compressibility and highly curved Mohr-Coulomb failure envelopes. The use of the spherical cavity expansion method offers potential for a better prediction of end-bearing capacities by taking into account soil crushability and the decrease of friction angle with increasing mean normal stress. A formula relating end-bearing pressure to the pressure to expand a cavity and the soil secant friction angle has been developed, which refines and simplifies Vesic's original equations. However, the actual model pile settlement ratio at which the predicted cavity expansion values were reached increased with soil crushability and decreased with increasing relative density. A simple linear relationship has been proposed between a soil compressibility index C_P and the pile settlement ratio at which the bearmg capacity predicted by the theoretical cavity expansion method is mobilized.