Model Loading Tests on Bearing Behaviour of a Group Pile and Ground Deformation in Sand

Model loading tests were conducted in dry sand to investigate the mechanism of pile-soil-pile interaction under group pile loading. The group pile was constituted of 9 (3x3) closed-end piles when the spacing between pile centres were 2.5 times of the pile diameter (2.5D) and 5.0 times (5.0D). The results showed that (1) yielding settlement of 2.5D group pile was larger than that of 5D group pile, (2) the subgrade reaction of the 2.5D group pile became less than that of the 5.0D group pile or a single pile when the load-settlement relationship was linear; (3) subgrade reactions of 2.5D and 5.0D group pile became similar after yielding of bearing load. Ground deformation was studied using with visualising tests and PIV analysis. It was shown that the ground deformation occurred as a block in case of 2.5D group pile and the deformed area expanded deeper as compared with 5.0D group pile. This mode of ground deformation reduced the subgrade reaction in 2.5D group pile.