Experimental Investigation for Group Efficiency of Driven Piles Embedded in Cohesionless Soil

In cases where stiffness and bearing capacity of soil aren’t sufficient to carry loads of a structure, depth of the foundation of the structure can be increased by using a pile group to transmit the loads to the soil layers with high bearing capacity. The behaviour of the pile group is discrepant with the response of a single pile due to the pile-pile and the pile-soil interactions. Therefore, extensive experimental and numerical studies have been performed for reliable and economical design of the pile groups. Even so, group efficiency (η) received no attention from researchers. Therefore, it is intended to investigate experimentally the group efficiency in this study. The pile groups with different pile spacings were tested in sandy soil with loading tests. The tests were performed at various relative densities and L/D ratios with the pile groups. After the small-scale tests, the determined group efficiency was compared with the existing methods. As a result, the influences of the pile length, diameter, spacing, and relative density on the group efficiency are investigated. From the results of the tests, it was found that although the conventional empirical formulas on pile group behaviour is that group efficiency is smaller than 1, the group efficiency for driven piles in cohesionless soils ranged between about 1.31 and 1.66 in this study.