Experimental Study of Compaction and Expansion Effects Caused by Penetration of Core Pile During Construction of SDCM Pile

Stiffened deep cement mixing (SDCM) piles have been applied in practice for decades. The bearing capacity of this kind of pile is closely related to the compaction and expansion of the deep cement mixing (DCM) pile and surrounding soil during penetration of the core pile. However, studies on driving behavior are scarce in the literature. Two sets of laboratory model tests will be conducted to facilitate the understanding of the response of an SDCM pile. The penetration depth of the core pile and the excess pore water pressure of the surrounding soil will be monitored using a string potentiometer and pore pressure transducers (PPTs). Diameter changes in the DCM pile before and after penetration of the core pile will be analyzed. Unconfined compressive strength (UCS) tests will be performed to investigate the mechanical properties of cement-treated soil with different densities. The results show that the excess pore water pressure of the surrounding soil increased during penetration of the core pile until the end of the core pile reached the depth of that position. The radius of influence was <7.90 times the diameter of the core pile. The normalized diameter of the DCM pile by its original diameter after penetration of the core pile was <1.05 at a depth of two times the core pile diameter below the end of the core pile, which indicated that the expansion effect that was caused by the penetration of the core pile was insignificant below that depth. In addition, the UCS and elastic modulus of the cement-treated soil increased linearly with density and the peak strain decreased.