The influence of foundation pit excavation on the surrounding soil pressure and deformation of existing shield tunnel in Xi'an loess stratum
LI Zhang1, BAI Sen1, ZHENG Jianguo2,3, YU Yongtang2,4, ZHU Caihui5*
1. China Railway Urban Development and Investment Group Co., Ltd., Chengdu 610218, Sichuan, China; 2. College of civil engineering, Xi'an University of Architecture and Technology, Xi'an 710055, Shaanxi, China; 3. China Mechanical Industry Survey and Design Research Institute Co., Ltd., Xi'an 710043, Shaanxi, China; 4. China United Northwest Engineering Design and Research Institute Co., Ltd., Xi'an 710077, Shaanxi, China; 5. Geotechnical Engineering Institute, Xi'an University of Technology, Xi'an 710048, Shaanxi, China
Abstract: In order to improve the safety of subway tunnel operation and provide a design basis for the planning of adjacent foundation pits, the deformation characteristics of existing subway segments and the surrounding soil pressure distribution under excavation unloading at different spatial locations were studied using a similar model test method based on Line 9 in the collapsible loess stratum in Xi'an. The influence zones of tunnel convergence displacement under the horizontal net distance between the foundation pit and the tunnel, the width, and the depth of the foundation pit were analyzed, and a modified formula of surrounding soil pressure was proposed. The results showed that the surrounding soil pressure of the shield tunnel exhibited a gourd-shaped symmetrical distribution before the excavation of the side foundation pit, with higher earth pressure at the top and bottom of the shield tunnel and lower pressure at the waist. After the excavation of the side foundation pit, the surrounding soil pressure on both sides of the tunnel decreased, with a more pronounced reduction on the excavation side. As the width and depth of the foundation pit increased and the horizontal net distance decreased, the absolute value of the additional surrounding soil pressure increased, and the deformation mode shifted to "lateral expansion and vertical contraction". After the excavation of the foundation pit directly above the tunnel, the overall surrounding soil pressure decreased significantly but retained a symmetrical distribution. With increasing width and depth of the foundation pit, the horizontal and vertical convergence deformation of the tunnel gradually diminished, approaching zero before transitioning to a "lateral contraction and vertical expansion" mode.
李璋,白森,郑建国,于永堂,朱才辉. 基坑开挖对西安黄土地层中既有盾构隧道围岩压力及变形影响分析[J]. 隧道与地下工程灾害防治, 2025, 7(1): 35-47.
LI Zhang, BAI Sen, ZHENG Jianguo, YU Yongtang, ZHU Caihui. The influence of foundation pit excavation on the surrounding soil pressure and deformation of existing shield tunnel in Xi'an loess stratum. Hazard Control in Tunnelling and Underground Engineering, 2025, 7(1): 35-47.
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2025, Vol. 7 
