Influence of axial load on lateral pile response in liquefiable soils. Part II: numerical modelling

Dynamic centrifuge modelling has been used to observe amplification of lateral displacements and unstable collapse in pile groups under the action of significant axial load and in liquefiable soils with low stiffness. The popular pseudostatic non-linear p-y analysis method has here been developed to account for such instability effects using the Riks post-buckling analysis method, here implemented in ABAQUS. The numerical method was validated against centrifuge model tests presented in the companion paper and pre-collapse amplification effects and collapse loads were found to be well predicted. The model was extended to examine the response of 2 x 2 pile groups formed from 0.5 m diameter piles with bending properties typical of steel and reinforced concrete and with initial deflections indicative of those that may occur during lateral spreading as a result of strong shaking. These analyses demonstrated the vulnerability of the flexible concrete piles to significant amplification and unstable collapse even at moderate loads, while for the stiffer and stronger steel piles, amplifications are only 10-20% even at maximum typical working loads, and therefore practically negligible in the design of piles in liquefiable soils.