含水率对坡积体路基填料剪切特性影响试验研究

坡积体是由坡面细流的侵蚀、搬运和沉积作用形成的一种土石混合体，含水率对其力学强度特性有重要影响。以陕西汉中略阳坡积体为研究对象，通过大型直剪试验分析坡积体重塑样在不同含水率条件下的应力应变特性、剪切"跳跃"特性、体积应变特性及抗剪强度参数变化规律。调研结果表明：略阳地区坡积体具有分布广、规模大、成因和结构构造复杂等分布特征，物质组成、结构构造和降雨是影响其工程特性的主要因素。室内大型直剪试验结果表明：含水率较低试样的应力-应变曲线可分为线弹性、局部剪切和剪切破坏3个阶段，而含水率较高试样只有前2个剪切阶段；低含水率试样的剪切"跳跃"现象主要发生在剪切初期，高含水率试样主要发生在剪切后期；低含水率试样在低应力下整体表现为剪胀，随着正应力的增加，剪胀量变小，而高含水率试样则表现为剪缩；高应力条件下试样全部表现为剪缩，且剪缩量随着含水率的增加而增大；剪切试样的抗剪强度整体上都是随着含水率的增大而降低，但降低幅度不大；试样的抗剪强度参数用内摩擦角和"等效黏聚力"表征，"等效黏聚力"随着含水率的增加先增大后减小，而内摩擦角则先减小后增大；土石混合填料抗剪强度曲线呈双线性变化。

Effect of Water Content on Shear Characteristics of Landslide Deposit Subgrade Fillers

Landslide deposits are a kind of soil-rock mixture formed by erosion, transport, and deposition of rivulets on a slope surface. Water content has an important influence on its mechanical strength characteristics. Therefore, this research aims to study the mechanisms of landslide deposit samples under different water contents by analyzing the characteristics of the stress-strain, "jumping" phenomenon, volumetric strain, and shear strength parameters in Lueyang County, China via large-scale direct shear tests. The investigation results show that landslide deposits in Lueyang area are widely distributed and mostly of a complex origin and structure. Material composition, structure, and rainfall are the main factors affecting their engineering characteristics. The large-scale direct shear test results show that the stress-strain curves of the specimens with lower water content can be divided into a linear elastic stage, shear stage, and failure stage, while specimens with higher water content only have the first two stages. The "jumping" phenomenon of lower water content specimens mainly occurs in the early stage of the shearing process, while the higher water content specimens mainly occur in the late stage. The lower water content specimens display dilatant behavior under low normal stress; the dilatancy value may become smaller with increasing normal stress. While specimens with higher water content show shrinkage behavior, both showed shrinkage behavior under high normal stress; the shrinkage value increases by increasing water content. This indicates that the intercept of the Mohr failure envelope of the sample should be called the "pseudo-cohesion or equivalent-cohesion", not simply "cohesion". The equivalent-cohesion value increases first and then decreases with the increase of water content, while the internal friction angle decreases first and then increases. Finally, a bilinear shear strength criterion for soil-rock mixtures is proposed.