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Study on the Impact of Foundation Pit Construction on the Deformation of Operating Metro Tunnels and Impact Zoning
(1.Key Laboratory of Road and Railway Engineering Safety of Ministry of Education，Shijiazhuang Tiedao University，Shijiazhuang 050043; 2. Shijiazhuang Institute of Railway Technology, Shijiazhuang 050041; 3. Xinjiang Railway Survey and Design Institute Co., Ltd., Urumqi 830011)
Abstract Based on the new transfer passage project of Beijing Metro, a combined approach of model experiment and numerical simulation was used to study the variation law of vertical displacement of existing tunnel structure caused by foundation pit excavation. The deformation mode of the existing structure was analyzed based on differential settlement under different approaching distances (B) and cover depths (h). The concept of an approaching coefficient was proposed, and a impact zoning of foundation pit construction was made according to its relationship with differential settlement. Four typical ground conditions were used to assess the risk levels of foundation pit excavation. The study showed that with the excavation of the foundation pit, the settlement of the tunnel structure exhibits a“slow-fast-slow”growth trend. Differential settlement of the existing tunnel structure caused by foundation pit construction decreases as the approaching distance increases, and increases then decreases with cover depth, ultimately reaching zero at infinite distance. When the ratio of approaching distance to cover depth (B/h) is constant, the differen? tial settlement caused by foundation pit construction is also a constant value. Based on the relationship between the approaching coefficient (k) and differential settlement, it is concluded that when 0.1 ≤ k < 5.0, it is a high-impact zone, and when k ≥ 5.0, it is a low-impact zone. The risk levels of foundation pit excavation in four typical ground conditions were identified as follows: soft soil stratum > alluvial-proluvial stratum > loess stratum > hard rock stratum.
Abstract：
Based on the new transfer passage project of Beijing Metro, a combined approach of model experiment and numerical simulation was used to study the variation law of vertical displacement of existing tunnel structure caused by foundation pit excavation. The deformation mode of the existing structure was analyzed based on differential settlement under different approaching distances (B) and cover depths (h). The concept of an approaching coefficient was proposed, and a impact zoning of foundation pit construction was made according to its relationship with differential settlement. Four typical ground conditions were used to assess the risk levels of foundation pit excavation. The study showed that with the excavation of the foundation pit, the settlement of the tunnel structure exhibits a“slow-fast-slow”growth trend. Differential settlement of the existing tunnel structure caused by foundation pit construction decreases as the approaching distance increases, and increases then decreases with cover depth, ultimately reaching zero at infinite distance. When the ratio of approaching distance to cover depth (B/h) is constant, the differen? tial settlement caused by foundation pit construction is also a constant value. Based on the relationship between the approaching coefficient (k) and differential settlement, it is concluded that when 0.1 ≤ k < 5.0, it is a high-impact zone, and when k ≥ 5.0, it is a low-impact zone. The risk levels of foundation pit excavation in four typical ground conditions were identified as follows: soft soil stratum > alluvial-proluvial stratum > loess stratum > hard rock stratum.
HU Zhinan1 MAO Hongtao1 LIU Zhichun1 LIU Zhanliang2 MENG Xiangfei3
.Study on the Impact of Foundation Pit Construction on the Deformation of Operating Metro Tunnels and Impact Zoning[J] MODERN TUNNELLING TECHNOLOGY, 2025,V62(1): 66-73
2025, Vol. 62 