Measured and Computed Lateral Response of a Pile Group in Sand

A lateral load test was performed on a full-scale pile group to evaluate pile–soil–pile interaction effects. The 3×3 pile group at 3.3 pile diameter spacing was driven opened ended into a profile consisting of loose to medium dense sand underlain by clay. The load carried by each pile was measured and strain gages were attached to determine bending moment. A single pile test was conducted for comparison. Group effects significantly reduced lateral resistance for all rows relative to single pile behavior. Trailing rows carried less load than the leading row. In contrast to tests in clay, lateral resistance was also consistently lower for middle piles within each row. Backcalculated p-multipliers were 0.8 for the front row and 0.4 for the trailing row piles which is consistent with results from previous centrifuge tests and full-scale tests where different installation methods were used. Good agreement between measured and computed pile group response was obtained using the pmultiplier approach. Based on centrifuge and full-scale tests in sands, design curves are presented to estimate p-multipliers over a range of pile spacings. The computer program SWM was able to match the measured group response without the use of p-multipliers.