Abstract: The CFG pile composite foundation offers notable environmental advantages and has seen extensive utilization for foundational stabilization in recent years. Surface soil load-bearing capacity deteriorates due to the inferior engineering properties of natural foundations, coupled with disruptions originating from CFG pile construction. Upon load application on the composite foundation, the CFG piles, behaving as rigid bodies, can easily cause an excessive pile-soil stress ratio, which is detrimental to the composite foundation’s interaction and inflicts damage upon the cushion layer. In view of this, we put forward the substitution of the 50 cm thick severely disturbed topsoil with compacted crushed stones, followed by the application of a cement-soil cushion to establish an innovative embedded cushion layer structure, geared towards the augmentation of the CFG pile composite foundation’s bearing capacity. The findings are as follows: in-situ load tests on single CFG pile composite foundation revealed that the pile-soil stress ratio within the embedded cushion layer was considerably less than that in traditional cushion layer conditions under the ultimate load, dropping from 22.9 to 13.8, a decrease of approximately 40% compared to traditional cushion layer conditions. Additionally, the pile-soil stress ratio curve was smoother, with no significant precipitous decline in pile-soil stress ratio after reaching ultimate bearing capacity, which is favorable for the foundation’s secure loading. Mathematical simulation methods were employed to model the vertical load characteristic of the CFG pile group composite foundation. The embedded cushion layer contributed significantly to the comprehensive fortification of the compression layers, thereby mitigating the piles’ relative penetration into the cushion layer. This resulted in a more uniform deformation of the cushion layer, effectively curtailing local penetration and uplift. Damage to the cushion layer structure caused by extreme pile soil stress ratios could be circumvented accordingly. Lastly, the embedded cushion layer enhanced the horizontal deformation state of CFG piles at different parts. The increased constraint at the top transformed the stress pattern of CFG piles from an ‘approximate cantilever’ to being ‘approximately simply supported’, thereby ameliorating the deformation and stress state of the side and corner piles.

Key words: CFG pile composite foundation, pile-soil stress ratio, embedded mattress layer, load test, numerical calculation