A Novel Prediction Method of Shear Strength of CFG Pile Composite Foundation in Soft Soil

ABSTRACT In the equivalent area method, composite foundations are simplified as homogeneous materials, by which the efficiency of shear strength calculation is significantly improved. This method has been widely applied in the quick evaluation of subgrade stability. However, the interaction between piles and soil, as well as the actual failure modes of composite foundations are neglected. As a result, deviations between the predicted and actual shear strength are often observed. In this study, direct shear tests and discrete element numerical simulations were conducted. The shear mechanical properties of CFG pile composite foundations were systematically investigated from both macroscopic and microscopic perspectives. Based on the findings, a modified equivalent area method was proposed and validated. The results indicate that significant differences in the shear strength and failure mode exist between soft soil and CFG piles. As the replacement area radio increases, the shear strength of the composite foundation significantly increases, and the failure mode of the pile changes accordingly. During shearing, the piles and the surrounding soil gradually form a coherent overall structure that undergoes coordinated deformation and jointly bears the shear load. The piles near the shear direction exhibit denser particle displacement, crack distribution, and bond failure, showing a progressive failure pattern. The shear strength calculated by the modified method is more conservative than that obtained by the equivalent area method. The modified method can more accurately reflect the actual situation of the composite foundation.