Stability analysis of expansive soil slopes considering shear strength decay characteristics
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摘要:
针对传统膨胀土边坡稳定性分析中无法考虑膨胀土在降雨入渗过程中抗剪强度动态衰减的问题，本文开展了室内直剪试验，系统研究了干密度和含水量变化对膨胀土抗剪强度指标的影响；同时，以试验抗剪强度结果为参数，开展了基于强度折减法的膨胀土边坡稳定性分析，获得了抗剪强度动态衰减过程中边坡稳定性的变化规律。结果表明，含水量的增加和干密度降低会造成膨胀土黏聚力和内摩擦角的衰减，黏聚力衰减显著，内摩擦角衰减较少；膨胀土边坡稳定性主要受风化层土体含水量控制，随着膨胀土含水量的增加，膨胀土边坡逐渐由稳定状态演变为欠稳定状态；干密度对膨胀土边坡稳定性的影响则相对较小。
Abstract:In order to address the problem that the dynamic decay of shear strength of expansive soil in the process of rainfall infiltration cannot be considered in the traditional slope stability analysis of expansive soil, indoor direct shear test was carried out to systematically study the influence of dry density and water content on the indicators of shear strength of expansive soil, viz., cohesion and internal friction angle. At the same time, the stability analysis of the expansive soil slope based on the strength reduction method was carried out with the shear strength testing results, and the change law of slope stability with the dynamic decay of shear strength was obtained. The results show that the increase of water content and the decrease of dry density will cause the decay of cohesion and internal friction angle of expansive soil, and the decay of cohesion is significant, while the decay of internal friction angle is less; the stability of expansive soil slope is mainly controlled by the water content of weathering layer, and with the increase of water content of expansive soil, the slope gradually evolves from stable state to unstable state, while the influence of dry density on the stability of expansive soil slope is relatively small.
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表 1 宁明膨胀土基本土体参数
Table 1. Basic soil parameters of Ningming expansive soil
参数 Gs/（g.cm−3） wL/% wP/% IP σf/% 取值 2.80 59.11 24.68 34.43 42.8 
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表 2 宁明膨胀土抗剪强度试验结果表
Table 2. Results of shear strength of Ningming expensive soils
试验参数 w/% φ/（°） c/kPa 试验结果 8.80 27.3 100.36 11.7 24.56 93.28 14.6 21.80 67.34 17.5 19.82 54.64 20.8 17.92 41.22 23.3 15.20 30.86 26.1 12.38 9.90
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表 3 宁明膨胀土黏聚力衰减率计算结果表
Table 3. Results of cohesion decay rate of Ningming expansive soil
试验参数 w/% c/kPa η/% 试验结果 8.8 100.36 − 11.7 93.28 7.05 14.6 67.34 27.81 17.5 54.64 18.86 20.8 41.22 24.56 23.3 30.86 25.13 26.1 9.9 67.92
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表 4 不同干密度下试样试验结果记录表
Table 4. Record table of test results under different dry densities
试验参数 ρd/（g·cm−3） c/（kPa） φ/（°） 试验结果 1.7 97.26 26.5 1.6 54.64 19.82 1.5 40.34 17.82 1.4 37.57 16.87
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表 5 土层相关参数
Table 5. Soil layer related parameters
地层岩性 厚度
/m重度
/（kN·m−3）内摩擦角
/（°）黏聚力
/kPa其它 填土①1 0.2~1 18.0 5 24 成分黏土 填土①2 2.5~3.3 18.8 30 7 上层砾砂，
下层碎石黏土② 0.3~4 18.4 8.4 35.6 中等膨胀土 强风化泥岩③ 0.6~1 19.3 25 45 质量等级Ⅴ级 中风化泥岩④ 未钻穿 19.6 35 65 质量等级Ⅴ级
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