Calculation and analysis of settlement of deep cement mixing pile composite foundation for Shenzhen-Zhongshan Link immersed tunnel

Based on the on-site test results of the deep cement mixing (DCM) pile composite foundation of the immersed tunnel in Shenzhen-Zhongshan Link, the influence of thick cushion and high replacement rate of DCM piles on load transfer mechanism and settlement characteristics of the composite foundation were considered. The gravel cushion, DCM pile composite foundation, and underlying layer at the pile end were regarded as a synergistic system, and the stress and deformation coordination of each part of the system on the contact surface were considered. The theoretical calculation formulas for the pile-soil stress ratio and settlement of submarine DCM pile composite foundation were derived by analyzing a typical unit. The load-displacement curve and pile-soil stress ratio variation curve of the DCM pile composite foundation obtained from theoretical calculation were compared with the measured curve of the on-site static load test, and the relative errors of both were within ±10%, verifying the rationality of the proposed theoretical calculation formulas. Further analysis was conducted on the influence of replacement rate and cushion flexibility coefficient on the load transfer mechanism and settlement characteristics of submarine DCM pile composite foundation. Results show that the settlement of composite foundation increases with the increase of cushion flexibility coefficient and decreases with the increase of replacement rate, the pile-soil stress ratio of composite foundation increases with the increase of replacement rate and decreases with the increase of cushion flexibility coefficient. Replacement rate has a greater impact on settlement and pile-soil stress ratio of composite foundation than cushion flexibility coefficient. © 2024 Zhejiang University. All rights reserved.