NUMERICAL ANALYSIS FOR TWO-STAGE EARTH BERM SUPPORT OF A DEEP EXCAVATION IN BEIJING SUB-CENTRAL STATION
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摘要:
在大型深基坑工程中,反压土支护由于经济性好、施工方便而得到了越来越多的应用,但是现有基坑规范并未给出设计方法。亚洲最大的地下综合交通枢纽北京城市副中心站V区基坑采用两级反压土支护,开挖深度达34.4 m,变形控制要求严格。通过三维数值模拟研究其支护效果,建立包含19个计算阶段的有限元模型,并基于相关试验结果确定了适用于北京地区土层的HSs模型参数。有限元预测结果表明该支护体系能够满足工程要求,反压土支护效果明显。同时,对比分析了小应变模型与常用的摩尔-库伦模型的计算结果,发现即便人为提高摩尔-库伦模型刚度,由于其单一模量的特点,仍无法得到合理的变形预测,深基坑变形计算中必须考虑土体小应变刚度特性,但是摩尔-库伦模型对支挡结构内力的计算结果与小应变模型比较接近。
Abstract:In large-scale deep excavation, earth berm support has been widely used due to economy and convenient construction, but the existing standards do not give a design method. The V-area excavation of Beijing Sub-Central Station, the largest underground comprehensive transportation hub in Asia, is supported by two-stage earth berm, with an excavation depth of 34.4 m and strict deformation requirements. The support effect was studied through three-dimensional numerical simulation, a finite element model containing 19 calculation stages was established, and the HSs model parameters suitable for the soil layer in Beijing were determined based on relevant test results. The finite element prediction results show that the support system can meet the engineering requirements, and the supporting effect of the earth berm is significant. At the same time, the calculation results of the small strain model and the commonly used Mohr-Coulomb model was compared, the results of which show even if the stiffness of the Mohr-Coulomb model is artificially increased, reasonable deformation prediction cannot be obtained due to its single modulus parameter, as a result, the small strain stiffness of soil must be considered in the deformation calculation of deep excavation, but the Mohr-Coulomb model is close to the small strain model in the calculation of the internal force of the supporting structure.
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Keywords:
- deep excavation /
- earth berm /
- finite element analysis /
- small strain stiffness /
- constitutive model
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表 1 支护结构尺寸
Table 1 Sizes of supporting structures
支护结构 尺寸 地连墙 厚度1 m 排桩 直径1.2 m、间距1.4 m 立柱 直径1 m、间距10 m 工程桩 直径2 m、间距10 m B3层顶板 厚度0.6 m B3层底板 厚度1.5 m B3层侧墙 厚度1.9 m B2层顶板 厚度0.3 m B2层边跨底板 厚度2.7 m B2层侧墙 厚度2 m 斜撑 截面0.8 m×0.8 m、间距4.5 m 表 2 HSs模型参数取值
Table 2 Parameters for HSs model
参数 取值 c′ 砂土:考虑湿砂取小值3 kPa
粉土与粉质粘土:根据地勘报告测孔压CU试验取值φ′ 砂土:根据地勘报告休止角取值
粉土与粉质粘土:根据地勘报告测孔压CU试验取值Rf 0.9 νur 0.2 Knc0 1−sinφ′ ψ ψ=φ′−30∘,若φ′<30∘,则取ψ=0∘ pref 100 kPa Erefoed 地勘报告给出了Es1-2,考虑取土扰动取Erefoed=Es1-2 Eref50 砂土:Eref50=Es1-2
粉土:Eref50=2Es1-2
粉质黏土:Eref50=Es1-2Erefur 砂土:Erefur=4Es1-2
粉土:Erefur=6Es1-2
粉质黏土:Erefur=5Es1-2m 砂土:0.5
粉土:0.6
粉质黏土:0.8Gref0 根据剪切波波速用公式G0=ρV2s计算G0,再根据应力水平换算成Gref0 γ0.7 砂土:4×10−4
粉土:3.5×10−4
粉质黏土:3×10−4表 3 各土层HSs模型参数取值
Table 3 Parameters of each soil layer for HSs model
土层编号 土性 厚度/m γ/(kN/m3) c′/kPa φ′/(°) m γ0.7 Erefoed/MPa Eref50/MPa Erefur/MPa Gref0/MPa ① 素填土 1.5 19.0 15.0 23.0 0.8 3.0×10−4 7.7 7.7 38.4 106.8 ② 黏质粉土-砂质粉土 6.0 19.4 10.0 30.0 0.6 3.5×10−4 9.2 18.5 55.4 120.4 ③ 细砂-中砂 6.0 19.5 3.0 32.0 0.5 4.0×10−4 30.0 30.0 120.0 143.5 ④ 细砂-中砂 5.9 20.0 3.0 32.0 0.5 4.0×10−4 32.5 32.5 130.0 157.9 ⑤ 细砂-中砂 10.1 20.5 3.0 32.0 0.5 4.0×10−4 35.0 35.0 140.0 200.9 ⑥1 重粉质黏土-粉质黏土 2.3 19.4 20.0 22.5 0.8 3.0×10−4 14.6 14.6 72.9 239.2 ⑥ 细砂-中砂 3.7 20.1 3.0 34.0 0.5 4.0×10−4 37.5 37.5 150.0 256.8 ⑦ 粉质黏土-重粉质黏土 4.0 19.8 19.6 23.5 0.8 3.0×10−4 18.2 18.2 91.2 263.4 ⑦1 黏质粉土-砂质粉土 5.0 20.6 8.0 35.5 0.6 3.5×10−4 29.4 58.8 176.3 264.5 ⑧ 细砂-中砂 6.0 20.3 3.0 35.0 0.5 4.0×10−4 40.0 40.0 160.0 277.3 ⑨1 粉质黏土-重粉质黏土 4.0 19.9 14.0 24.0 0.8 3.0×10−4 20.8 20.8 104.2 232.3 ⑨ 细砂-中砂 2.0 20.3 3.0 36.0 0.5 4.0×10−4 42.5 42.5 170.0 217.0 ⑩ 粉质黏土-重粉质黏土 4.0 20.1 15.2 24.0 0.8 3.0×10−4 23.6 23.6 118.0 169.2 ⑪ 细砂-中砂 13.0 20.5 3.0 36.0 0.5 4.0×10−4 45.0 45.0 180.0 245.8 ⑫1 重粉质黏土-粉质黏土 2.0 19.9 14.2 24.0 0.8 3.0×10−4 24.0 24.0 120.2 179.3 ⑫ 细砂-中砂 9.0 20.5 3.0 36.0 0.5 4.0×10−4 47.5 47.5 190.0 266.4 ⑬ 粉质黏土-重粉质黏土 4.0 20.3 13.7 24.0 0.8 3.0×10−4 28.8 28.8 143.9 217.9 ⑬1 细砂-中砂 5.0 20.5 3.0 38.0 0.5 4.0×10−4 50.0 50.0 200.0 239.6 ⑭ 粉质黏土-重粉质黏土 4.0 20.1 15.0 24.0 0.8 3.0×10−4 30.4 30.4 152.2 217.6 ⑭1 中砂-细砂 2.5 20.5 3.0 38.0 0.5 4.0×10−4 52.5 52.5 210.0 271.9 -
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