On the behaviour of pile groups under combined lateral and vertical loading

- The influence of vertical loads in the lateral response of pile group, commonly neglected in traditional design approaches, should be accounted.
- The percentages of changes in the lateral capacities of piles due to vertical loads are very significant.
- Depending on the soil type and the pile position, the vertical loads greatly affect the group interaction factor (p-multiplier).

The effect of vertical loads on the lateral response of a 3×5 pile group embedded in sandy and clayey soils is studied through 3D finite differences analyses using the computer code FLAC3D. In the numerical model, the piles were treated as a linear elastic material and the soil was idealized using the Mohr-Coulomb constitutive model with a non-associated flow rule. Vertical loads, inducing a vertical pile head displacement of 0.01-pile diameter, were applied prior to the application of the lateral loads. Numerical results showed that the lateral resistances of the piles installed in sandy soil increase with vertical loads. However, the presence of vertical loads on piles embedded in clay reasonably decreases their lateral capacities. The increase and decrease in the lateral stress in the sandy and clayey soils, respectively, are the major driving factors to contribute the change in the lateral resistance of piles, depending on the pile position in the group and its lateral deflection. The distribution of lateral loads among piles in the group tends to be more uniform when vertical loads were considered leading to a more economical pile foundation design.