Design practice of deep and complex foundation pit based on local conditions and displacement control
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摘要: 北京城区某基坑深度约16.5 m，局部加深部位约20.4 m，基坑周边分布大量管线与住宅楼，开挖深度范围内涉及多层地下水。基坑地下水控制设计采用厚搭接落底式帷幕隔水，有效地解决了地下水渗漏问题，抑制了周边地层附加沉降，对控制周边建筑变形起到了积极作用；于基坑周边及局部深坑外围因地制宜布设应急减压井，有效地保障了水下锚杆施工，同时对承压水突涌起到了积极的防控作用。基坑支护设计遵循位移控制设计理念，通过数值分析与理论计算相结合对深基坑变形进行预测，提出支护结构位移控制标准，根据周边环境的敏感程度选取不同刚度的支护体系，并有针对性地提出锚杆施工工艺要求及地下水控制配合措施，在节约工期和造价的同时有效地保障了基坑及周边环境的安全和正常使用。Abstract: A foundation pit excavation was located in Beijing urban area with a depth of approximately 16.5 meters, with a local deepened area of up to 20.4 meters. Surrounding the excavation were numerous utility lines and residential buildings, as well as multiple layers of groundwater within the excavation depth range. The groundwater control design utilized a thick overlapping bottom-fall curtain wall to effectively solve the problem of groundwater seepage, suppressed the additional settlement of surrounding soil layers, and played a positive role in controlling the deformation of surrounding buildings. According to the local condition, emergency depressurization wells were set up around the excavation and in the local deepened area, effectively ensuring the construction of water-submerged anchor rods and playing a positive role in preventing the sudden surge of confined water. The foundation pit support design adhered to the principle of displacement control, combining numerical and theoretical calculations to predict the deformation of deep foundation pit. A standard for the displacement control of support structures was proposed, and different stiffness support systems were selected based on the degree of sensitivity of the surrounding environment. Specific requirements were also made for the construction process of anchor rods and water control measures to effectively ensure the safety and normal use of the foundation pit and surrounding environment while saving time and costs.
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表 1 主要地层物理力学参数表
地层 重度
/(kN·m−3)c/kPa φ/(°) m
/(MPa·m−2)qs/kPa ①房渣土 19 8 12 4.96 25 ③砂质粉土–黏质粉土 20 22 25 24.4 65 ③1粉质黏土–黏质粉土 19.9 25 20 17 55 ④1细砂–中砂 20.4 0 30 30 100 ④圆砾–卵石 21 0 45 72 160 ⑤黏质粉土–砂质粉土 20 20 25 24 75 ⑤1粉质黏土–黏质粉土 20 25 22 19.96 65 ⑥卵石 21.5 0 45 72 200 
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表 2 地下水水位量测情况
地下水
类型稳定水位（水头） 含水层 埋深/m 标高/m 第1层
（潜水）14.79～15.96 22.83～23.51 ④层、⑤层 第2层
（承压水）16.77～17.52 21.24～21.49 ⑥层
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表 3 周边建筑物变形监测值统计表
mm 楼座 隆起 沉降 楼座 隆起 沉降 26号楼 0.5 −2.9 32号楼 0.7 −3.6 27号楼 3.5 −2.8 锅炉房 2.7 −2.3 30号楼 0.6 −4.0 水泵房 9.4 −1.5 31号楼 5.5 −8.6 区政府 1.9 −2.5
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