Experimental investigation of pile diameter and group configuration effects on soil pile interaction and lateral group efficiency in sand

This laboratory study investigates the influence of pile diameter and group configuration on the lateral response of piles embedded in dry sand. Pile models with diameters of 8, 16, and 45 mm were tested as single piles and in triangular 3-pile and 6-pile groups to evaluate soil–pile interaction effects on piles with different flexural stiffness. Results indicate that piles with varying bending stiffness exhibit significantly different lateral load-bearing behavior despite identical lengths and equal spacing conditions. The findings show that lateral group efficiency is governed by the combined influence of energy dissipation within the soil–pile system and the effective lateral load-bearing surface area. Smaller diameter piles experience earlier plastic deformation in both the pile and surrounding soil, increasing energy dissipation, whereas larger diameters provide greater contact area but create more severe soil disturbance, limiting resistance mobilization around adjacent piles. Among the tested piles, the pile with intermediate flexural stiffness exhibited the highest performance, achieving a lateral efficiency ratio greater than unity in the 3-pile configuration and significantly outperforming piles with smaller and larger diameters. The results also highlight the importance of selecting appropriate displacement criteria when evaluating lateral pile group efficiency, particularly for piles with higher bending stiffness.