加筋粗粒土强度变形特性试验研究

Experimental Research on Strength-Deformation Characteristics of Reinforced Coarse-Grained Soil

采用大型三轴仪与大型直剪仪,对粗粒土、加筋土强度变形特性进行了实验研究。直剪试验结果表明:不同竖向荷载下粗粒土和加筋粗粒土剪切的剪应力-剪切位移关系类似,应力应变曲线均出现应变软化现象,但软化特性变化不大;加筋土法向位移-剪切位移变化曲线表现为法向应力越低,剪胀现象越明显;粗粒土加筋后的内聚力增加,但是内摩擦角却降低。三轴试验结果表明,不同围压条件下粗粒土和加筋土主应力差与轴向应变关系曲线表现为应变硬化型,围压越大,主应力差与轴向应变关系曲线越陡,应变硬化特性越明显,最大主应力差越大;围压越低,剪胀作用越明显,越容易由剪缩发展到剪胀,反之围压越高,则剪缩作用越明显;当轴向应变较小时,加筋效果不明显,随着轴向应变的逐渐增大,加筋效果逐渐发挥。加筋土的内聚力明显大于粗粒土,而内摩擦角基本上相等;利用三轴试验结果对邓肯-张模型的适用性进行了分析研究,表明邓肯-张模型能合理地确定粗粒土与加筋土的强度以及切线弹性模量,但难以描述和确定粗粒土的变形特性和切线泊松比,且不能反映粗粒土的剪胀性。

An experimental research was conducted on strength-deformation characteristics of reinforced coarse-grained soil by employing a large-scale triaxial and direct shear apparatus. The large-scale direct shear test showed similar relations of shear stress to shear displacement for coarse-grained and reinforced coarse-grained soil under different vertical load, and strain softening appearing on both stress-strain curves without great change in softening characteristics. It can be seen from the curve of normal displacement to shear displacement for reinforced coarse-grained soil that shear dilatation turned to be more noticeable with lower normal strain, and coarse-grained soil got an enhanced cohesion, but a smaller internal friction angle after being reinforced. Then from the triaxial shearing test, a relation curve of deviator stress and axial strain of coarse-grained soil before and after being reinforced under the conditions of different confining pressure was obtained showing strain hardening characteristics. With an increase in the confining pressure, the relation of deviator stress and axial strain turned to be a steeper curve, with more significant strain hardening characteristics and greater difference in the maximum principle stress. While a decreased confining pressure brought about a more noticeable shear dilatation due to the shear contraction liable to become shear dilatation, and vice versa. Besides, the smaller axial strain resulted in an unobvious reinforcement effect, and only with the increasing of axial strain, the reinforcement effect turned to be noticeable. Compared with coarse-grained soils, the reinforced coarse-grained soil gets a larger cohesion, but almost similar internal friction angle. After analyzing applicability of Duncan-Chang material model with the tri-axial shearing test results, it is concluded that Duncan-Chang material model can reasonably determine the strength and tangent modulus of elasticity for coarse-grained and reinforced soil. However, it can′t be used to describe and define deformation characteristics and tangent Poisson′s ratio, neither reflect the shear dilatation of coarse-grained soil.