基于大津法(Otsu)多阈值分割方法，利用数字图像处理技术获取了花岗岩细观结构的表征图像，并结合颗粒流程序，重构了反映岩石非均质结构特征的细观模型。通过单轴压缩试验，分析了花岗岩的失稳破坏过程，并研究了细观结构强度对宏观强度及破坏形态的影响。研究发现：花岗岩试件失稳破坏过程中存在4种裂纹形式，加载初期首先产生界面裂纹，其次是云母裂纹，长石和石英在应力接近极限强度时才破坏；当增大胶结界面或矿物强度时，花岗岩的抗压强度随之增加，但增加梯度逐渐减小；胶结界面或3种矿物细观强度的增大会使该结构处裂纹数量减小，而增加其他结构处的裂纹分布；相对于中等强度的长石和高强度的石英，低强度的胶结界面和云母矿物对花岗岩宏观强度和破坏形态的影响较大，是关键细观结构。将Otsu图像处理技术与颗粒流程序相结合，建立反映岩石真实结构的细观模型，为研究岩石非均质性对宏观力学特性的影响提供了一种有效手段。

Based on the multi-threshold Otsu method, the characteristic image of granite microstructures is obtained by using the digital image processing method, and a mesoscopic model, which can reflect the actual heterogeneous structural properties, is reconstructed using Particle Flow Code. With conducting the uniaxial compressing tests based on the propoed model, the failure process and the effect of mesostructured (interface, mica, feldspar and quartz) on failure strength are analyzed. The results show that there are four types of cracks in the failure process of the granite. In the initial loading stage, cracks generate in the interface, and then in mica; when stress is close to the peak value, the cracks begin to generate in feldspar and quartz. As the strength of interface or mineral increases, the compressive strength of the granite increases, while the gradient of growth decreases. The increase of the strength of interface or the minerals can lead to a reduction in the number of cracks corresponding to the interface or the minerals, which can increase cracks in other areas. Compared to the feldspar with moderate strength and the quartz with high strength, the interface and mica are the key mesostructures that can significantly influence the granite compressive strength and failure modes. Combining Otsu digital image processing with PFC, a mesoscopic model of rocks is rebuilt, which provides an effective method for studying the mechanical properties of heterogeneous rocks.