P-y Curves of 2x2 pile group in liquefiable soil under dynamic loadings

Abstract

The seismic analysis of pile groups subjected to lateral and axial loads is often implemented separately. As a result, the calculated bending moment and deflection are found to be nonrealistic in nature, as compared with conditions where a combined analysis is carried out. In reality combined loadings are encountered in almost all situations and the occurrence of pure loadings (either lateral or vertical) is either nonexistent or scarce. In the present study, the numerical analysis of a 2 × 2 pile group under the action of combined loadings (lateral load, vertical load, and seismic ground motions) and embedded in a layered soil is carried out using the FLAC3D computer program. The liquefiable soil layer is modeled using the Mohr-Coulomb with Byrne constitutive model, while the non-liquefiable soil layers are modeled with the conventional Mohr-Coulomb constitutive model. The pile group is considered an elastic model. The proposed numerical model is validated with the existing dynamic centrifuge test results and good agreement between the results is observed. Finally the dynamic P-y (P denotes the lateral load applied at the pile cap and y is the lateral pile group deflection at the pile head) curves are generated for different combinations of vertical load, lateral load, and input seismic ground motions in liquefiable and non-liquefiable soil. It is observed that for a constant vertical load (V) having a magnitude equal to 0.50 times the ultimate pile load capacity (0.50Vult), the pile group deflection increases by 36% when the lateral load increases from 300 to 900 kN, while the increase is by 48.5% for V = Vult and for the same increase in the lateral load. Similarly 2001 Bhuj and 2011 Sikkim motions caused an amplification of deflection by 8.4 and 9 times, respectively. The influence of vertical loads increases the pile head displacement and should be considered for determining the dynamic P-y curves. The proposed dynamic P-y curves will be beneficial to geotechnical engineers for understanding the qualitative response of pile groups under combined loading conditions.