预制裂隙花岗岩的强度特征与破坏模式试验

为了探究单轴压缩条件下裂隙岩石的强度特性、裂纹起裂规律及破坏模式, 采用水刀切割技术预制裂隙花岗岩试件, 利用GAW2000刚性试验机对单裂隙花岗岩试样进行单轴压缩试验.试验结果表明: 与完整试样相比, 裂隙岩石试样单轴抗压强度明显降低, 降低幅度与预制裂隙和外荷载方向的夹角β密切相关, β=75°时, 强度最低, 降幅达到84.5%, 基于最大畸变能准则计算了裂隙花岗岩的峰值抗压强度与裂隙倾角的关系, 试验结果与数值解吻合; 裂隙的存在改变了岩石的破坏模式, 裂纹起裂角随裂隙倾角的增加而单调增大, 岩石试样的破坏模式由剪切破坏为主转变为张拉破坏占主导.真实裂隙岩石试样的力学性质及裂纹起裂特征更准确地揭示了单裂隙花岗岩的强度变化规律和破坏模式, 为岩土工程设计和巷道裂隙围岩体的支护提供科学依据. 

Experiment on the strength characteristics and failure modes of granite with pre-existing cracks

Rock masses are typically anisotropic discontinuous materials composed of joints, fractures, and interlayers. Many instability and failure cases in geotechnical engineering have been induced by the expansion and transfixion of cracks in the rock masses. The mechanical properties and fracture characteristics of joints usually determine the bearing capacities and fracture modes of rocks. As such, the investigation of the crack initiation and expansion law, strength, and deformation characteristics of fractured rock masses has great significance. In this study, the rock samples investigated were taken from deep zones in the Sanshandao gold mine, where the surrounding rock masses are fractured and the maintenance costs of deep tunnels are very high. To investigate the mechanical behaviors of fractured rock masses, uniaxial compression experiments were conducted on granite samples with pre-existing cracks. First, cracks were generated in cylindrical rock samples by a water-jet cutter. Then, the rock samples with cracks and intact samples were compressively tested using a rigid testing machine (GAW2000) to determine their strength characteristics, crack initiation rules, and failure modes. The experimental results show that the uniaxial compressive strength (UCS) values of granite samples with pre-existing cracks are lower than those of intact samples, and the extent of the UCS reduction is closely related to β, i.e., the angle between the pre-existing crack and the direction of the external load. When β is 75°, the UCS values of the samples are at their minimum, and the reduction rate reaches 84.5%. These experimental results are in good agreement with the numerical solution of the maximum distortion energy criterion. Pre-existing cracks change the failure modes of rocks. With an increase in the dip angle of a pre-existing crack, the crack initiation angle increases monotonically, and the failure mode of the rock sample changes from shear failure to tensile failure. The mechanical properties and crack initiation characteristics of real-fracture rock samples can more accurately reveal the strength characteristics and failure modes of fissured granite, and thereby provide a scientific basis for the support of fractured rock masses and geotechnical engineering design.