A pair of dynamic tests was performed on pile-group foundation models under both uniaxial and biaxial shakings

by use of the biaxial shaking table at the HKUST centrifuge. By comparing the bending moments developed on the piles

it is found that the symmetric property of pile-group foundation response observed under the uniaxial shaking does not exist any more when under the biaxial shaking. The results of numerical tests using PFC2D provide some explanation to the phenomenon of orthogonal loading effect. At the same time

the limitation of currently used analysis methods for soil-pile interaction is pointed out based on some derivation. The paper presents the preliminary study on soil-pile interaction under multidirectional horizontal loading

so as to provide basis and reference for further study along this line.