Engineering evaluation method for overall stability of slurry trenches
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摘要: 当前分层地基中地下连续墙成槽整体稳定性验算多采用水平条分法。当槽段宽度与成槽深度比相对较小时,三维水平条分法所给出的计算结果可能偏于不安全。此外,验算时一般采用有效抗剪强度指标并按水土分算原则验算成槽稳定性。然而在当前我国大量的工程实践中,地质勘察报告往往仅提供直剪固结快剪强度指标,如何结合工程实践现状验算槽壁稳定性值得进一步的研究。首先介绍了水平条分法的理论框架,并详细讨论了水平条分法与楔形体滑体模式的内在联系。随后结合某一现场试验展开案例分析,指出了饱和黏土中三维楔形体模式存在的不足,并提出一种基于三维等效楔形体的改进方法。最后结合10个工程案例的验算结果,分析了二维与三维水平条分法在计算结果上的差异,以及强度指标选取和水土压力计算原则对分析结果的影响,为今后的工程实践提供参考。Abstract: The horizontal slice method is commonly used for examining the trench stability in layered soils. Unsafe results may be given by the 3D horizontal slice method when the ratio of trench length to depth is relatively small. In addition, the effective soil strength parameters are recommended for trench stability analysis. However, the soil strength parameters in engineering reports are often obtained from the direct shear tests. Further investigation is needed to incorporate the trench stability analysis with the current practice. In this study, the theoretical framework of the horizontal slice method is introduced, and its connection with the sliding wedge method is discussed. The deficiency of the 3D sliding wedge method in undrained clay is shown by a field test, and the improvement by an equivalent 3D wedge method is proposed. A discussion on influences of the differences between 2D and 3D methods, selection of soil strength parameters and water pressure calculation on the calculated results is carried out through 10 collected case studies.
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Keywords:
- slurry wall /
- trench stability /
- horizontal slice method /
- strength parameter /
- safety factor
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表 1 Vaterland现场试验对比
Table 1 Comparison for Vaterland site test
验算方法 Fs (油)Fs (泥浆)二维楔形体模式 0.40 0.53 土压力模式 0.57 0.73 地基承载力模式 0.85 1.48 三维楔形体模式 1.38 1.84 三维等效楔形体模式 0.95 1.26 三维极限分析有限元(上限/下限) 0.99/0.87 1.32/0.92 表 2 工程实例1土层参数
Table 2 Soil parameters for project 1
土层 埋深/m 重度/(kN·m-3) ccq /kPaφcq /(°)①素填土 0~1.55 18.0 10 8 ①素填土 1.55~3.85 18.0 10 8 ②-1淤泥质土 3.85~6.40 16.3 8 5 ②-2细砂 6.40~10.70 17.5 1 25 ②-3粉质黏土 10.70~11.95 18.0 22 15 ③-1粉质黏土 11.95~15.20 18.5 25 18 ③-2粉质黏土 15.20~18.10 19.0 32 25 表 3 工程实例2土层参数
Table 3 Soil parameters for project 2
土层 埋深/m 重度/(kN·m-3) ccq /kPaφcq /(°)①-1杂填土 0~1.80 17.5 10 8 ①-1杂填土 1.80~2.66 17.5 10 8 ②-1淤泥质粉质黏土 2.66~4.48 16.5 8 6 ②-2淤泥质土 4.48~6.47 16.5 6 5 ②-3粉质黏土 6.47~10.53 18.5 24 16 ②-4粉土 10.53~12.43 19.5 25 18 ③-1粉质黏土 12.43~14.90 19.5 28 19 ④-1全风化泥质粉砂岩 14.90~18.60 20.0 24 25 ④-2强风化泥质粉砂岩 18.60~21.80 21.0 60 30 表 4 工程实例3土层参数
Table 4 Soil parameters for project 3
土层 埋深/m 重度/(kN·m-3) ccq /kPaφcq /(°)①-1杂填土 0~3.17 18.1 10 10 ①-1杂填土 3.17~4.99 18.1 10 10 ①-3素填土 4.99~10.73 18.1 13 10 ①-4耕植土 10.73~11.73 18.1 10 10 ②-1粉质黏土 11.73~15.71 19.1 25 15 ②-2淤泥质黏土 15.71~18.35 16.8 6 4 ②-3黏土 18.35~19.00 19.2 28 16 表 5 工程实例4土层参数
Table 5 Soil parameters for project 4
土层 K0 埋深/m 重度/(kN·m-3) ccq /kPaφcq /(°)①-2素填土 0.45 0~2.25 18.4 11.1 13.6 ②-2淤泥质粉质黏土 0.60 2.25~3.17 17.7 8.4 11.8 ②-2淤泥质粉质黏土 0.65 3.17~8.50 17.7 8.4 11.8 ②-3A粉土夹粉质黏土 0.55 8.50~11.05 18.0 9.8 18.9 ②-3粉质黏土夹粉土 0.58 11.05~18.15 17.8 10.4 16.4 ②-4A粉土夹粉砂 0.47 18.15~22.15 18.5 8.5 23.3 ②-4粉质黏土夹粉土 0.50 22.15~27.40 18.0 10.5 16.2 ②-5粉砂夹粉土 0.45 27.40~35.00 18.3 1.8 22.3 ②-6粉细砂 0.42 35.00~62.30 18.5 1.5 33.0 表 6 工程实例5土层参数
Table 6 Soil parameters for project 5
土层 埋深/m 重度/(kN·m-3) ccq /kPaφcq /(°)①填土 0~0.77 18.0 5 10 ①填土 0.77~2.30 18.0 5 10 ②-1黏土 2.30~4.30 18.0 22 13 ③黏土 4.30~5.60 17.5 16 11 ⑥1-1黏土 5.60~8.98 19.3 48 17 ⑥1-2粉质黏土 8.98~17.98 18.6 30 17 ⑥-2粉质黏土 17.98~25.00 18.6 24 16 表 7 工程实例6土层参数
Table 7 Soil parameters for project 6
土层 埋深/m 重度/(kN·m-3) ccq /kPaφcq /(°)c′ /kPaφ′ /(°)K0 ①素填土 0~1.00 18.5 22 19.5 7 27.4 0.45 ①素填土 1.00~1.56 18.5 22 19.5 7 27.4 0.45 ②-3黏质粉土 1.56~6.33 18.3 6 30.0 (0) (25.2) 0.37 ③淤泥质粉质黏土 6.33~11.59 17.4 11 18.5 0 30.1 0.45 ④淤泥质黏土 11.59~18.44 16.5 9 11.5 3 21.2 0.57 ⑤-1黏土 18.44~21.76 17.3 14 13.5 6 21.9 0.52 ⑤-2砂质粉土 21.76~25.60 18.3 5 33.5 (0) (26.9) 0.36 ⑤3-1粉质黏土 25.60~32.90 18.0 14 19.5 4 29.8 0.47 注: 土层②-3及⑤-2有效抗剪强度指标按式(25)计算得到。表 8 工程实例7土层参数
Table 8 Soil parameters for project 7
土层 埋深/m 重度/(kN·m-3) ccq /kPaφcq /(°)①-1素填土 0~2.1 19.5 12 8 ①-1素填土 2.1~2.6 19.5 12 8 ②-1砂质黏土 2.6~4.8 19.5 20 13 ②-2细砂 4.8~6.5 19.7 0 20 ②-3中粗砂 6.5~8.8 19.5 0 25 ②-4黏土 8.8~10.4 18.7 20 8 ②-5淤泥质土 10.4~11.3 16.8 10 4 ②-6砾砂 11.3~12.6 20.8 0 30 ③残积砾质黏性土 12.6~16.0 18.1 20 18 ④-1全风化花岗岩 16.0~18.3 18.6 22 22 ④-2-1强风化花岗岩上段 18.3~20.5 18.9 25 25 表 9 工程实例8土层参数(深隧项目)
Table 9 Soil parameters for project 8
土层 埋深/m 重度/(kN·m-3) ccq /kPaφcq /(°)c′ /kPaφ′ /(°)ccu /kPaφcu /(°)K0 ②-1粉质黏土 0~1.75 18.1 23 17.5 6 26.5 22 21.3 (0.50) ②-3黏质粉土 1.75~2.28 18.2 7 30.5 (0) (31.5) — — 0.40 ②-3黏质粉土 2.28~14.07 18.2 7 30.5 (0) (31.5) — — 0.40 ③淤泥质粉质黏土 14.07~19.70 17.1 12 14.0 2 29.6 10 18.0 0.50 ④淤泥质黏土 19.70~26.53 16.6 14 12.0 3 27.9 13 16.6 0.53 ⑤-1黏土 26.53~33.60 17.2 17 16.0 4 30.5 18 19.6 0.51 ⑤-3粉质黏土夹粉砂 33.60~46.91 17.5 19 19.0 5 31.6 20 21.4 0.47 ⑤-4粉质黏土 46.91~49.57 19.1 47 16.0 16 32.4 48 24.3 0.47 ⑦粉砂夹粉质黏土 49.57~55.06 19.0 7 31.5 (0) (34.5) — — 0.37 ⑧-1粉质黏土 55.06~61.74 17.6 22 17.5 8 32.4 24 23.9 0.48 ⑧-2粉质黏土粉砂互层 61.74~77.97 18.3 30 20.5 8 33.1 24 26.4 0.47 ⑨-1粉砂夹粉质黏土 77.97~81.28 19.6 0 36.0 (0) (25.2) — — 0.35 ⑨夹粉质黏土夹粉砂 81.28~83.32 19.1 19 24.5 (0) (30.5) — — (0.45) ⑨-2-1粉细砂夹中粗砂 83.32~91.85 20.4 0 36.0 (0) (25.2) — — 0.33 ⑨-2-2中粗砂 91.85~103.39 20.4 0 36.0 (0) (25.2) — — 0.34 ⑩黏土 103.39~105.00 20.0 92 20.5 19 31.6 92 19.0 0.51 注: 土层②-3、⑦、⑨、⑨-1、⑨-2-1、⑨-2-2有效抗剪强度指标按式(25)计算得到。表 10 工程实例9土层参数
Table 10 Soil parameters for project 9
土层 埋深/m 重度/(kN·m-3) ccq /kPaφcq /(°)②粉质黏土 0~1.52 18.3 14 14.0 ③淤泥质粉质黏土 1.52~3.00 17.5 8 17.5 ③淤泥质粉质黏土 3.00~5.46 17.5 8 17.5 ④淤泥质黏土 5.46~13.06 16.7 9 9.5 ⑤1-1黏土 13.06~18.94 17.5 12 11.0 ⑤1-2粉质黏土 18.94~25.33 18.0 12 14.0 ⑤3-1粉质黏土夹黏质粉土 25.33~35.20 18.1 9 16.5 ⑤3-2粉质黏土 35.20~40.43 18.1 12 18.0 ⑤-4粉质黏土 40.43~43.75 19.7 38 18.0 ⑦-1砂质粉土 43.75~46.83 19.1 4 29.0 ⑦2-1粉砂 46.83~59.04 19.0 1 32.0 ⑦-2夹粉质黏土夹砂质粉土 59.04~61.72 18.9 7 26.5 ⑦2-2粉砂 61.72~68.82 18.9 1 32.0 ⑨粉砂 68.82~75.00 19.0 1 31.0 表 11 工程实例10土层参数
Table 11 Soil parameters for project 10
土层 埋深/m 重度/(kN·m-3) ccq /kPaφcq /(°)①杂填土 0~1.40 18.0 10 15.0 ②粉质黏土 1.40~1.54 18.6 24 17.0 ②粉质黏土 1.54~3.00 18.6 24 17.0 ③淤泥质粉质黏土 3.00~3.70 17.3 12 17.5 ③夹砂质粉土夹淤泥质粉质黏土 3.70~10.40 18.4 8 26.5 ④淤泥质黏土 10.40~18.00 16.7 14 11.0 ⑤1-1黏土 18.00~23.10 17.1 16 12.0 ⑤1-2粉质黏土 23.10~24.50 17.7 17 15.0 表 12 验算结果汇总表
Table 12 Summary of safety factor
安全系数3D/2D 方法1 ccq,φcq 分算方法2 ccq,φcq 合算方法3 c′,φ′ 分算方法4砂性土 c′,φ′ 分算黏性土ccu,φcu 分算方法5砂性土 c′,φ′ 分算黏性土ccu,φcu 合算算例1——鸿晖大厦 2.64/1.48 2.94/1.79 算例2——君豪国际商业城 2.75/1.61 3.05/1.83 算例3——广州三号线 2.27/0.87 2.77/1.25 算例4——南京世茂 2.67/0.95 3.03/1.84 算例5——东渡悦来城 2.45/1.12 2.73/1.94 算例6——西岸传媒港 2.31/0.79 3.85/1.61 1.80/0.81 算例7——城建大厦 2.19/1.02 2.88/1.49 算例8——苏州河调蓄工程 2.53/0.75 4.26/1.71 2.41/0.84 2.43/0.78 2.76/1.51 算例9——徐家汇中心 2.11/0.63 2.74/1.25 算例10——9号线 2.00/0.66 3.21/1.31 -
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