Effect of loading direction on the ultimate lateral soil pressure of two piles in clay

Design equations are presented for the calculation of the ultimate lateral resistance of two-pile groups in clay under a general loading direction. Analytical upper bound solutions, numerical upper and lower bound limit analyses and displacement finite-element analyses are first presented for the case of two piles loaded parallel to the pile-to-pile axis. Displacement finite-element analyses are subsequently used to calculate the ultimate lateral resistance for different directions of pile displacement. The design equations that are proposed, based on the numerical study, take account of the effect of the pile spacing, the pile–soil adhesion and the displacement or the loading direction on the ultimate lateral resistance.