Group Reduction Factors for the Analysis of the Pile Groups Under Combination of Lateral Loads in Sandy Soils

Very limited studies have investigated the behavior of laterally loaded pile group systems. Accurate prediction of load-displacement response is essential in a pile group to produce a safe and economical design. The nonlinear soil-pile interactive behavior is commonly modeled by p-y curves. The p-y curve of a single pile in a pile group system is modified using a specific p-multiplier for each row of the piles to obtain group reduction factor (P-m) and consider the effects of a pile group. This paper experimentally and numerically investigates the effects of various parameters on the lateral response of piles and p-multiplier in a pile group. Small-scale tests of laterally loaded piles were performed, and a three-dimensional finite element model was validated based on the experimental load-displacement curves. The soil was modeled as an elastic-perfectly plastic material using the modified Mohr-Coulomb constitutive model. The validated model was then used to run parametric studies to evaluate the influence of factors including pile spacing (S), group arrangement, and lateral load combination. The results indicated that the calculated values of P-m for one-way lateral loads at S/D = 3 (S: spacing, D: pile diameter) were close to the values recommended by bridge design specification, AASHTO. However, AASHTO underestimated the group reduction factors and lateral resistance for two-way or angular lateral loads.