Analysis on Deformation Characteristics of Super Large Diameter Ring Bracing Deep Foundation Pit in Soft Soil near Subway
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摘要: 以深圳都市茗荟花园(二期)基坑为工程背景,对超大直径圆环撑软土深基坑支护桩侧向变形、地面沉降、支撑轴力等监测数据进行了分析,分析了基坑变形的时空分布特征,探讨了基坑变形与开挖深度、软土厚度的关系,得出下列结论:(1)支护结构的最大变形随着基坑开挖深度的增加而逐步增大,基坑开挖至坑底后,整体变形最大位置位于基坑两侧长边中部采用圆环支撑部位。(2)咬合桩+刚度较大的超大直径环形钢筋砼撑结构应用于软土深基坑中在变形控制及减小基坑工程对周边变形影响等方面均非常有效。(3)随着基坑向下不断开挖,三种方式所反映出的支护结构的最大水平位移量均逐渐增加,但变化幅度有一定的差异。Abstract: Taking the foundation pit of Minghui Garden (phase II) in Shenzhen reclamation area as the engineering background, the monitoring data of lateral deformation, slope top displacement and support axial force caused by foundation pit construction were analyzed. The temporal and spatial distribution characteristics of deep foundation pit deformation in soft soil were discussed, and the relationship between foundation pit deformation and excavation depth as well as soft soil thickness was discussed. The conclusions were as followed: (1) The maximum deformation of the supporting structure gradually increases with the increase of the excavation depth of the foundation pit. After the foundation pit was excavated to the bottom of the pit, the maximum overall deformation was located at the middle of the long side on both sides of the foundation pit, which was supported by a ring. (2) The application of bite pile + super large diameter ring reinforced concrete support structure with large stiffness in soft soil deep foundation pit was very effective in deformation control and reducing the influence of foundation pit engineering on surrounding deformation. (3) With the continuous excavation of the foundation pit downward, the maximum horizontal displacement of the support structure reflected by the three methods gradually increases, but the variation range was different.
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表 1 各土层物理、力学指标
土层 重度/(kN·m−3) 变形模量/MPa 泊松比 黏聚力/kPa 内摩擦角/(°) 杂填土 19.0 10 0.33 15 12 淤泥 18.5 5 0.35 8 5 含砂粉质黏土 19.0 20 0.30 25 18 粗砂 21.5 30 0.25 0 30 砾质黏性土 19.5 35 0.22 25 20 表 2 主要开挖工况
开挖工况 时间(年-月) 工况1(开挖至第一道支撑底,施工第一道支撑) 2019-02 工况2(开挖至第二道支撑底,施工第二道支撑) 2019-05 工况3(开挖至基坑底) 2019-11 工况4(拆除第二道支撑) 2020-05 工况5(拆除第一道支撑) 2020-07 表 3 基坑周边勘察钻孔信息统计
监测点 邻近钻孔
编号填土
厚度/m淤泥
厚度/m粗砂
厚度/m桩身最大
变形/mmX1 ZK72 2.5 5.8 3.5 21.81 X2 ZK71 2.5 6 4.3 24.84 X3 ZK44 3.0 5.9 4.0 23.32 X4 ZK42 2.5 6.2 3.0 22.54 X5 ZK1 2.9 5.3 2.7 13.42 X6 ZK23 2.1 5.8 4.9 15.65 X7 ZK14 3.0 5.2 6.5 15.15 X8 ZK41 2.4 5.4 4.6 16.15 X9 ZK49 2.3 5.3 8.1 18.36 表 4 施工工况与支护桩最大位移量统计
施工工况 开挖深度/m X1最大位移/mm X3最大位移/mm X6最大位移/mm X9最大位移/mm 开挖至第一道
支撑底2.0 2.22 8.23 2.97 1.31 开挖至第二道
支撑底8.0 7.22 17.35 12.19 8.30 开挖至基坑底 13.45 21.81 23.31 15.64 18.35 拆除第二道支撑 13.45 23.81 25.43 15.95 26.89 拆除第一道支撑 13.45 26.18 26.11 16.65 26.87 表 5 施工工况与最大坡顶位移量统计
施工工况 开挖深度/m CW5最大地面沉降/mm CW9最大地面沉降/mm CW17最大地面沉降/mm CW30最大地面沉降/mm 开挖至第一道支撑底 2 −4.3 −6.4 −2.1 −1.1 开挖至第二道支撑底 8 −6.6 −10.2 −5.1 −5.8 开挖至基坑底 13.45 −14.9 −17.4 −10.9 −13.2 拆除第二道支撑 13.45 −17.6 −23.6 −12.7 −20.7 拆除第一道支撑 13.45 −18.2 −24.3 −13.2 −20.9 表 6 各监测点邻近地质勘察孔各软弱土层厚度统计
监测点 邻近钻孔 填土厚度
/m淤泥厚度
/m粗砂厚度
/m地面沉降
/mm监测点 邻近钻孔 填土厚度
/m淤泥厚度
/m粗砂厚度
/m地面沉降
/mmCW1 ZK74 5.5 2.5 4.5 −9.6 CW17 ZK12 2.1 6.8 4.8 −10.9 CW2 ZK74 5.5 2.5 4.5 −13.4 CW18 ZK10 4.3 4.9 2.7 −11.2 CW3 ZK73 2.5 5 2.9 −11.9 CW19 ZK23 2.1 5.8 4.9 −7.7 CW4 ZK71 3.5 6 4.3 −15.1 CW20 ZK23 2.1 5.8 4.9 −8.9 CW5 ZK70 3.0 5.6 4.5 −14.9 CW21 ZK24 2.1 5.5 4.6 −10.1 CW6 ZK68 5.0 3.4 4.5 −14.5 CW22 ZK11 3.1 5.2 0.0 −8.9 CW7 ZK68 5.0 3.4 4.5 −14.6 CW23 ZK11 3.1 5.2 0.0 −10.2 CW8 ZK44 3.0 5.2 4.0 −14 CW24 ZK12 2.1 6.8 4.8 −9.1 CW9 ZK42 4.5 6.2 3.0 −17.4 CW25 ZK14 2.9 6.0 0.0 −11 CW10 ZK33 2.3 5.3 4.7 −12.5 CW26 ZK16 1.6 7.3 1.8 −10.2 CW11 ZK28 2.9 6.4 0.0 −10.4 CW27 ZK19 2.3 0.0 0.0 −6.9 CW12 ZK20 3.0 4.8 6.4 −14.6 CW28 ZK27 2.3 5.8 5.1 −10.2 CW13 ZK3 3.0 4.2 2.0 −13.1 CW29 ZK41 2.4 5.4 4.6 −8.3 CW14 ZK2 2.0 5.5 5.4 −8.6 CW30 ZK49 2.3 5.3 8.1 −13.2 CW15 ZK1 2.9 5.3 2.7 −10.7 CW31 ZK67 4.5 3.0 3.5 −11.8 CW16 ZK8 2.5 5.8 0.0 −10.5 CW32 ZK61 2.5 5.8 3.1 −9.5 -
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