中文摘要：

应用RFPA^3D分别模拟了理想光滑端部加载和限制性加载端部情况下不同形状的岩石在单轴压缩下的破坏过程。模拟结果表明，试样形状对岩石的抗压强度、变形特征以及破坏模式有很大影响。岩石试样的强度随着长宽比的增加而减小，当长宽比超过2．5以后单轴压缩强度趋于稳定。理想端部下，长宽比较大的试样主要是剪切破坏模式；而长宽比较小时，主要是因为拉伸引起破坏。端部效应是引起试样拉伸破坏的一个重要因素，但是即使采用光滑端部，试样的形状效应依然存在。长宽比的逐渐增加使岩石逐渐由延性破坏向脆性破坏转变。

英文摘要：

A three-dimensional soften model is established combined with statistical mechanics to take the heterogeneities on mesoscopic scale into consideration. Two sets of numerical tests are undertaken by using a numerical code RFPA^3D to analyze the failure process of rocks subjected to uniaxial compression. Numerical specimens are prepared to investigate the influence of the geometry effects on the macro response of the rocks. One set of numerical tests are conducted without constraint and there are no friction between the loading plates and the specimens, Another set of numerical tests compared with laboratory experiments are conducted to simulate the geometry effect by taking end constraint effect into consideration. Numerical results show that the geometry of specimen influences both the peak strength and failure mode. The peak strength decreases as the ratio of length to width of the specimen increases; and it inclines to a certain value when the ratio exceeds 3.0. When the ratio is small, the failure of the specimens are caused by tensile fracture propagating the top and the bottom of specimens; while the ratio is larger enough, specimens tend to be in shear failure mode. End constraint effect is one of the key factors that lead to geometry effects. The plate restricts the lateral deformation and results in lateral stress in the middle of the specimen, which leads to tensile failure. However, geometry effects still exist even with smooth plates. The transition of the ductile failure mode to brittle mode can be found as the ratio of the length to the width of the specimens increase.