Efficiency of pile groups in sand soil under lateral static loads

To predict the pile group behavior under lateral loads, the p-multiplier approach is commonly used to modify the p-y curves of single piles with different P-multipliers for the leading row and the trailing rows. But under reversible cyclic loading, an average p-multiplier called "group reduction factor" for all piles in the group is reasonably used. In this paper, three-dimensional modeling is conducted using MIDAS GTS-NX software tool to understand the behavior of pile groups in sand under lateral load and validated versus a well-instrumented full-scale case study reported by Rollins et al. (J. Geotech. Geoenviron. Eng.ASCE, 131(1):103, 2005). The effect of different parameters such as the spacing between piles (3, 4, and 5 times the pile's diameter), the group size (3 x 3, 4 x 4, and 5 x 5), the sand's internal friction angle (30-40), and the pile head condition (free or fixed) are studied to evaluate the group efficiency under lateral loads. The computed group reduction factors in this study are then compared to different previous experimental tests' results and different design curves. The result of the study shows a good agreement with the results of some previous experimental tests and design guidelines. However, some guidelines such as the Federal Emergency Management Agency (FEMA P-751), the American Association of State Highway and Transportation Officials (AASHTO), and Reese and Van Impe (Single piles and pile groups under lateral loading, Boca Raton, Florida, USA, 2010) are too conservative regarding the group reduction factors especially for large pile groups and for fixed-head pile groups, and this could be attributed to the fact that their recommendations are based on the results of small free-head pile groups.