The group effect of the lateral soil pressure acting on the passive pile shafts was an important problem.Using the explicit finite difference code FLAC3 D

the group effect of the lateral soil pressure along the pile shaft for coupled passive stiff piles（center to center"joining"line being in the directon of applied soil movements）with pined-head and pined-tip condition and uniform soil movement was investigated.The Mohr-Columb elastic-plastic constitutive model was employed to model the non-linear stress-strain soil behaviour and the coupled piles were assumed to have linear elastic behaviour and the interface model incorporated in FLAC3 Dcode has been used to simulate the soil/pile contact.The results given by the numerical analysis indicated that the lateral soil pressures on the coupled passive piles were lower than those for single passive piles

the lateral soil pressure on the"near"pile was higher than those for"far"pile.In the shallow soil

The reinforcing effect was not obvious

but the shadowing effect was remarkable.In the deep soil

the reinforcing effect and the shadowing effect were all remarkable.The shape of the p-δcurves was different from the single pile.After a short linear rise

the lateral soil pressure experienced a non-linear growth before achieving the limiting soil pressure.The magnitude of relative displacement to mobilize the limiting soil pressure was more than those for single passive piles.When the pile spacing increased to 6times the pile diameter

the group effect became very small.In the end

the group factors of ultimate soil pressure for various pile spacings were summarized and compared with the result of the laboratory model test in the literature.