干湿循环作用下预崩解炭质泥岩裂隙发育规律及强度特性

由于炭质泥岩遇水易风化、强度低、变形大，干湿循环作用下炭质泥岩路堤易形成纵横交错的裂隙网络，加速路堤边坡失稳。为分析干湿循环作用下预崩解炭质泥岩裂隙演化规律与强度特性，通过制备较大尺寸预崩解炭质泥岩试样，开展室外裂隙演化原位试验及裂隙试样直剪试验，实时拍摄不同干湿循环次数下试样裂隙扩展图像，并基于裂隙图像特征参数对各阶段裂隙特征进行定量化描述，进而构建预崩解炭质泥岩的抗剪强度与裂隙参数关系模型。研究结果表明：预崩解炭质泥岩裂隙数量、裂隙最大长度及裂隙率等裂隙参数均随干湿循环次数分为迅速增长、缓慢增长、趋于平缓3个阶段；各因素对裂隙发育影响程度由强至弱依次为初始含水率、干密度、干湿循环次数；含裂隙试样剪切时遇到裂隙剪切应力会发生暂时性衰退，不同裂隙参数试样的黏聚力变化显著，而内摩擦角变化甚微，内摩擦角变化主要取决于土体干密度的变化，而黏聚力变化取决于初始含水率，抗剪强度主要与黏聚力相关联。为研究土体抗剪强度与裂隙参数的关系，拟合得到了裂隙率与黏聚力的指数关系模型，发现其拟合变化曲线呈凹形的抛物线变化，其抛物线分急剧降低和趋于稳定2个阶段。研究成果可为预崩解炭质泥岩路堤工程施工及稳定性分析提供参考。

Crack Development and Strength Characteristics of Pre-disintegrated Carbonaceous Mudstone Under Dry-wet Cycles

Because carbonaceous mudstones exhibit weak weathering resistance, low strength, and large deformation when they are exposed to water, crisscross crack networks easily form in carbonaceous mudstone embankments under dry-wet cycles, which accelerates the slope instability of this type of embankments. Large-sized pre-disintegrated carbonaceous mudstone (PCM) samples were produced to analyze the crack evolution and strength characteristics of the samples under dry-wet cycles. Outdoor crack-evolution in situ tests and direct shear tests were performed, and images of the crack expansion of the samples under different dry-wet cycles were captured in real-time. Based on the image parameters, the crack characteristics at various stages were quantitatively described, and a model that showed the relationship between the shear strength and the crack parameters of the PCM was developed. The results show that the crack parameters of the PCM, such as the number of cracks, the maximum length of cracks, and the crack rate, initially increase rapidly, subsequently increase slowly, and finally stabilize with the number of dry-wet cycles. According to their influences on the development of cracks, the examined parameters are ranked as the initial moisture content, dry density, and the number of dry-wet cycles successively from strong to weak. Temporary reductions of shear stress occur when the shear plane passes through cracks in a cracked sample. The cohesion of the samples with different crack parameters changes significantly, whereas the internal friction angle changes slightly. The change in the internal friction angle mainly depends on the change in the dry density of the soil. Moreover, the change in cohesion depends on the initial moisture content, and the shear strength is mainly correlated to cohesion. An exponential model was fitted to establish the relationship between the soil shear strength and crack parameters. It is found that the fitted curve is concave parabolic, and its parabola is divided into two stages, i.e., "sharply decreasing" and "tending to be stable". The results obtained in this study can provide references for the construction and stability analysis of PCM embankments.