Material point method simulations of displacement pile and CPT penetration in sand considering the effects of grain breakage

Full displacement installation dramatically alters the stress and strain fields applying around piles and Cone Penetrometer (CPT) probes at sand sites. Calibration chamber tests have indicated that severe particle crushing occurs near to the pile or cone tips and a distinct shear zone may develop that leaves crushed sand adhering to the pile or cone shaft. It is therefore important to investigate how particle breakage affects the stress and deformation fields developed as this process occurs. In this study, installation by monotonic jacking of conically tipped model piles or CPT probes into silica sand is simulated by material point method (MPM) analyses. A thermodynamically consistent model which considers competing grain crushing and dilation is employed to model the sand behavior, while an MPM approach is adopted to cater for the large deformations involved in the penetration process. Particle crushing is predicted beneath the pile tip and around the pile shaft. The numerical results are compared to directly related instrumented pile calibration chamber tests. The numerical results show that the computed stress and displacement fields match key aspects of the experimental results well, especially in reproducing the volumetric compression observed experimentally. The results confirm that combining MPM with suitably sophisticated constitutive models creates new capabilities for analyzing large-deformation problems.