Experimental study on fully softened shear strength of expansive soil
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摘要: 以引江济淮试验段工程项目为依托,开展膨胀土完全软化强度试验,分析了膨胀土完全软化强度指标在不同含水率、剪切速率下的变化规律,并在此基础上与膨胀土干湿循环强度指标展开对比分析。完全软化状态下,膨胀土黏聚力接近0,完全软化强度主要由内摩擦角决定;内摩擦角受含水率影响不大且几乎不受剪切速率影响;黏聚力普遍较小,符合完全软化状态黏聚力接近0的定义。分别采用干湿循环后强度指标和完全软化强度指标,对简单膨胀土边坡开展了干湿循环后浅层稳定性分析。结果表明,和干湿循环试验相比,完全软化试验工作量小,试验周期短,能反映膨胀土边坡浅层滑塌的破坏机理,可用以对膨胀土边坡受干湿循环作用后的浅层稳定性分析。Abstract: The fully softened strength tests are carried out on the expansive soil samples from the Yangtze-Huaihe River Water Transfer Project. The fully softened strength indexes under different moisture contents and shear rates are discussed and analyzed. On this basis, they are compared with the shear strength indexes from the wetting-drying cycle direct shear tests on expansive soil. The results show that in the fully softened state, the cohesive force of expansive soil is close to zero, and the fully softened strength is mainly determined by the inernal friction angle. The inernal friction angle is little affected by the moisture content and shear rate. The strength indexes obtained from wetting-dring cycle tests and fully softened tests are applied to the safety analysis of simple expansive soil slope respectively. Compared with the wetting-drying cycle direct shear tests, the fully softened strenght tests need less lab work and shorter test peroid. The fully softened strength indexes can also reflect the failure mechanism of the shallow failure of expansive soil slopes after wetting-drying cycles in practice. It is recommended to apply the fully softened strength indexes in the analysis of the shallow stability of expansive soil slopes after wetting-drying cycles.
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Keywords:
- expansive soil /
- fully softened strength /
- wetting-drying cycle /
- shallow failure
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表 1 完全软化试验设计方案
Table 1 Programs of fully softened tests
试验条件编号 试样含水率/% 剪切速率/(mm·min-1) #0 45.0 0.1,0.6,0.8,1.2 #1 47.5 0.1,0.6,0.8,1.2 #2 50.0 0.1,0.6,0.8,1.2 #3 52.5 0.1,0.6,0.8,1.2 #4 55.0 0.1,0.6,0.8,1.2 表 2 重塑样抗剪强度试验结果
Table 2 Shear strength results of remolded soil
法向应力/kPa 干湿循环次数 0 1 3 5 12.5 19.2 15.7 12.9 12.7 25.0 23.2 17.9 17.8 17.6 37.5 27.1 22.2 20.7 20.4 50.0 30.6 26.5 24.3 24.3 100 32.3 28.6 27.7 26.9 200 36.3 32.9 29.2 29.0 300 38.9 34.6 33.5 32.9 400 42.3 38.4 35.8 36.1 表 3 重塑样抗剪强度指标
Table 3 Shear strength indexes of remolded soil
循环次数 高应力段 低应力段 c/kPa ϕ/(°) c/kPa ϕ/(°) 0 29.3 1.9 15.5 17.6 1 25.9 1.9 11.4 16.4 3 24.3 1.6 9.6 16.6 5 23.6 1.8 9.3 16.7 注: 循环幅度为4%~31%,脱湿温度为40℃。表 4 膨胀土完全软化强度指标
Table 4 Fully softened shear strength indexes
土样含水率w/% 剪切速率/(mm·min-1) 0.1 0.6 0.8 1.2 c/kPa ϕ/(°) c/kPa ϕ/(°) c/kPa ϕ/(°) c/kPa ϕ/(°) 45.0 2.4 25.2 2.1 25.2 1.9 25.2 1.7 24.8 47.5 1.8 25.3 1.5 25.0 1.4 24.9 1.3 24.9 50.0 1.3 24.8 1.1 24.6 1.1 24.8 0.9 24.4 52.5 1.0 24.6 0.8 24.3 0.7 24.1 0.6 23.8 55.0 0.9 24.4 0.8 24.2 0.6 23.9 0.5 23.8 表 5 边坡土体抗剪强度指标
Table 5 Shear strength indexes of expansive soil slopes
土体埋深/m 初始强度指标 干湿循环强度指标 完全软化强度指标 c/kPa ϕ/(°) c/kPa ϕ/(°) c/kPa ϕ/(°) 0~2.5 15.5 17.6 9.3 16.7 0.6 23.9 2.5~4.0 29.3 1.9 23.6 1.8 4.0~9.0 29.3 1.9 29.3 1.9 29.3 1.9 -
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