Group Efficiency of Tension Double Under-Reamed Piles in Sand

During the last few years, many researchers have studied experimentally and numerically the behaviour of single under-reamed piles subjected to vertical forces in sand. Surprisingly, the uplift response and the uplift group efficiency of group double under-reamed piles embedded in sand subjected to uplift loads were never fully studied. As a result, in this paper, we carried out laboratory studies on different configurations of double under-reamed piles in groups subjected to uplift loads in different relative densities of dry sand. The effect of relative density, spacing between double under-reamed piles, and the number of piles in the group on the group efficiency of model groups was investigated. Hence, the influence of the corresponding parameters on the group efficiency was evaluated. The results showed that group efficiency of tension double under-reamed piles in all model tests was less than 100%. Furthermore, in the case of dense sand and double under-reamed pile spacing ratio equal four times the under-ream diameter, the group efficiency is found to be 79.18%, 65.28%, and 55.13% for two, three, and four pile configurations, respectively, while these values are found to be 86.75%, 81.14%, and 74.46% in loose sand in the same order. In addition, an analytical model based on the limit equilibrium approach was used to estimate the uplift capacity of group double under-reamed piles based on failure mode identification.