An experimental study of the stress-strain characteristics of frozen silty clay with high moisture content
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摘要: 为研究青藏高原粉质黏土在高含水量条件下的应力-应变特性，本文对粉质黏土试样开展了较高含水量（15%，30%，50%）、不同温度（-2℃，-4℃）及围压（0.5，1.0，2.0，4.0 MPa）条件下的三轴剪切试验，分析了冻粉黏土试样应力-应变曲线的形态和强度规律，并给出了机理性解释。试验结果表明：冻粉黏土试样的应力-应变曲线均为应变软化型。高含水量下（50%），试样的初始切线模量随围压增大呈幂函数形式增大。随着含水量的增大，试样的破坏过程渐呈脆性。试样强度方面，含水量的增大使冻粉黏土强度呈先减小后增大的规律，即存在一个强度最不利含水量。此最不利含水量主要是由于土骨架与冰相的组合使系统处于“最弱结构”以及各组分在承受荷载时的主次地位变换而引起的。围压增大使冻粉黏土强度线性降低，但降低幅度不大。结合Mohr-Coulomb准则的分析表明，黏聚力是冻粉黏土强度的主要指标，其值在最不利含水量时取得最小值，围压对冻粉黏土强度的削弱作用也在此时得以突显。Abstract: To study the stress-strain characteristics of the Qinghai –Tibet silty clay with high moisture content, triaxial shear tests were conducted on the silty clay under relatively high moisture contents (15%, 30% and 50%), different temperatures (-2 ℃ and -4 ℃) and confining pressures (0.5, 1.0, 2.0 and 4.0 MPa). The shape of the stress–strain curves and the strength characteristics of the frozen silty clay were analyzed and interpreted in mechanism. The test results show that the stress-strain curves of the frozen silty clay specimens are all of the strain-softening type. At high moisture content (50%), the initial tangential modulus of the specimen increases with the confining pressure in the form of power function. With the increasing moisture content, the failure process of the specimens tends to be brittle. The continuous increase in moisture content causes the strength of the frozen silty clay to decrease first and increase subsequently, that is to say, there exists an unfavorable moisture content for the shear strength. The existence of the unfavorable moisture content is mainly due to the “weakest mass structure” composed of soil skeleton and ice and to the transition of the leading role of each composition in bearing the external load. With the increasing confining pressure, the shear strength of the frozen silty clay decreases linearly, but the variation range is not large. The analysis based on the Mohr-Coulomb criterion shows that the cohesion is the main constituent of the strength of the frozen silty clay. The cohesion reaches a minimum at the most unfavorable moisture content, at which the weakening effect of the confining pressure on the strength is also strengthened.
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Key words:
- silty clay /
- triaxial test /
- shear strength /
- high moisture content
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