Experimental testing of a full-scale of group efficiency in multiple soil layers

Results of in-situ tests showed that the performance of single isolated piles and individual piles within a group is largely different. When piles are arranged in a group, the interaction between piles and the foundation depends on the pile arrangement and the pile group effect. To date, studies on the pile group effect in Vietnam have been limited to reduced-scale laboratory testing or static load testing where piles are installed into homogeneous sandy or clayey foundation. This paper presents in situ tests which were performed on both single piles and pile groups, loaded to failure, with the aim of studying the pile group effect of piles embedded in multi-layered foundation. Strain gauges were installed along the shaft of 10 m long steel pipe piles, with a diameter of 143 mm. The influence of loose sand layers on the group effect in case of friction piles was evaluated. The experimental results indicated that the influence of sand layers was evident, and the group factor was calculated to be 1.237. Keywords: group efficiency; pile groups; axial capacity; load transfer.