Abstract
Based on a deep foundation pit project for a cable tunnel, a numerical calculation model of the deep foundation pit and its supporting structure was established using MIDAS GTS NX software, and the numerical model was validated through analysis of field measurement data. The effects of parameters such as diaphragm wall thickness, cement mixing pile depth, diaphragm wall depth, and support stiffness on the deformation characteristics during excavation were investigated, and optimization design recommendations were proposed. The results show that greater diaphragm wall thickness leads to smaller displacement variations in the retaining structure and adjacent structures; however, when diaphragm wall thickness reaches 1.0 m, its effectiveness in restraining soil deformation becomes insignificant. The settlement of power tower foundations, displacement of underground pipelines, and ground surface settlement all decrease with increasing depth of diaphragm walls and mixing piles, yet when their depth reaches 35 m, the enhancement of foundation pit support effectiveness becomes negligible. It is recommended that the depth of diaphragm walls and concrete mixing piles be designed as 35 m. Although increasing support stiffness can reduce displacement variations in surrounding soil, its effect is less pronounced compared with increasing the depth of diaphragm walls and mixing piles.
Full Text
Parameter Optimization of Support Structures for Deep Foundation Pit Excavation in a Cable Tunnel Project
Zhuzhixiang
China Railway 16th Bureau Group Road and Bridge Engineering Co., Ltd., Beijing 101500, China
Abstract
This study addresses the parameter optimization of support structures for deep foundation pit excavation in a cable tunnel project. A numerical model of the deep excavation and its support system was developed using MIDAS GTS NX software and validated through comprehensive analysis of field monitoring data. The investigation focused on the effects of key design parameters—including diaphragm wall thickness, cement mixing pile depth, diaphragm wall depth, and support stiffness—on deformation behavior during excavation, yielding specific recommendations for optimized design.
The results indicate that increasing diaphragm wall thickness effectively reduces displacements in both the retaining structure and adjacent infrastructure. However, beyond a thickness of 1.0 m, the benefit for restraining soil deformation becomes marginal. The settlement of power tower foundations, displacement of underground pipelines, and surface settlement all decrease with increasing depths of the diaphragm wall and mixing piles, yet the improvement in support performance diminishes substantially when these depths exceed 35 m. Accordingly, a design depth of 35 m is recommended for both the diaphragm wall and cement mixing piles. While increasing support stiffness can also reduce displacements in surrounding soils, this approach proves less effective than increasing the embedment depths of the diaphragm wall and mixing piles.
Keywords: Cable tunnel; Deep foundation pit; Support structure; Parameter effect; Optimization