掺砾黏土在高心墙堆石坝工程中的应用越来越广泛，其拉伸断裂特性对心墙的安全至关重要。将掺砾黏土视作四相复合材料，基于图像处理和随机投放建立了考虑真实砾石形态的细观数值模型，结合物理试验的结果验证了其有效性，并分析了掺砾黏土拉伸断裂的宏细观特性。应力位移曲线的宏观非线性是细观非均质性的体现，砾石的掺入大幅减低了抗拉强度，但提高了峰后抗拉性能；土石界面是微裂缝发展的源头，拉伸断裂是一个微裂缝萌生、扩展以至汇集形成宏观裂缝的过程；拉伸断裂发生在一个区域，即断裂过程区，该区域的形成与砾石的随机分布有关。最后，采用数值试验分析了随机砾石投放和掺砾量对掺砾黏土宏细观力学行为的影响。

Clay mixed with gravel is becoming widely used as a core material of high earth and rockfill dams. Its tensile fracture characteristics are crucial to the safety of the core wall. Clay mixed with gravel is considered as a four-phase composite material and a mesoscopic numerical model is constructed via image processing and random packing to consider the real shape and distribution of gravels. With this model, whose effectiveness is validated by physical tests, the macroscopic and mesoscopic tensile fracture characteristics of clay mixed with gravel are analyzed. The nonlinear behavior on macro scale is due to mesoscopic heterogeneity. The addition of gravel greatly decreases the tensile strength but increases the post-peak tensile resistance. Soil-rock interfaces are the source of microcracks and tensile fracture is a process where microcracks initiate, propagate and coalesce to macrocrack. Tensile fracture occurs in a region, i.e. the fracture process zone, and the formation of this zone is related to the random distribution of gravels. Through numerical experiments, the influence of the random packing and content of gravel on the macroscopic and mesoscopic behaviors of clay mixed with gravel is analyzed.