Much research has been done to study the effects of spacing in laterally loaded pile groups and how the pile spacing affects lateral resistance of the piles. In this test a 9-pile group of steel piles was installed in a 3x3 configuration in sand. The piles were spaced from center-to-center at a distance of 5.65 pile diameters in the direction of the load. The pile group was laterally loaded and instrumented to collect deflection, load, and strain data. A separate single pile was similarly instrumented and tested for comparison to the pile group. The soil profile consisted of a top layer of sand about 2.5 meters deep underlain by alternating layers of fine grained soil and sand. Analysis was done in order to determine p-multipliers for the rows in the pile group. The pile group consistently resisted lower average loads than those of the single pile at the same peak deflection. Row 1 resisted equal loads to those resisted by the single pile but Row 2 and Row 3 resisted smaller loads successively. The maximum bending moments were greatest in Row 1 and decreased successively in Row 2 and Row 3, however they occurred at the same depth for the same peak deflection. Maximum bending moments for the single pile were similar to those for Row 1 in the pile group at each deflection. Group effects were more significant at greater loads with larger deflections. Higher deflection caused increased shear zone interaction and a decrease in lateral resistance. The test on the single pile was modeled using the computer program LPILE Plus version 4.0 (Reese et al., 2000). The soil profile was calibrated by alternating the input soil parameters until the curves matched between the measured and the calculated results. The new soil profile was then used to model the test on the pile group using GROUP version 4.0 (Reese and Wang, 1996). A match was made between the measured test results and those calculated using GROUP by defining p-multipliers for each of the rows. For Cycle 1 the p-multipliers were found to be 1.0, .55, and .5 for Row 1 through Row 3 respectively. For Cycle 10 the p-multipliers were found to be the same as those for Cycle 1.



College and Department

Ira A. Fulton College of Engineering and Technology; Civil and Environmental Engineering



Date Submitted


Document Type





Pile Groups, p-multipliers, sand, 5.65 pile diameter spacing