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以大理岩作为试验材料,进行了45°双预制裂纹试件的单、双轴加载和侧向卸载试验研究。利用高速摄影设备记录试件中裂纹的起裂、扩展、贯通和完全破坏过程,结合理论分析得到:(1)3种载荷形式下试件的破坏过程可概括为4个相似的阶段;双轴加载试件的裂纹扩展形态和岩桥贯通方式与单轴加载和卸载有较大不同;卸载试件的裂纹种类和数目远比单轴加载时更多更复杂。(2)由裂纹类型判断在单、双轴加载时,剪应力对破坏起主导作用;卸载时,尤其破坏前阶段拉应力起主导作用。(3)定义新参数M-C有效剪应力M-C,根据其在裂纹尖端附近的分布规律判定新裂纹起裂的危险方位和区域,对比试验过程,得到与预制裂纹夹角约为-135°和45°左右的区域为新裂纹(带)产生的危险区。(4)加载时岩桥贯通是由剪应力引起,卸载时是由拉剪复合作用引起。
Using marble as the test material, the uniaxial, biaxial and lateral unloading experiments of 45 ° double pre-cracked specimens were carried out. Using high-speed photographic equipment to record the crack initiation, propagation, penetration and complete destruction in the specimen, the theoretical analysis shows that: (1) The failure process of the specimens under three kinds of loading conditions can be summarized into four similar stages; biaxial The crack propagation mode and rock-through mode of loading rock specimen are different from those of uniaxial loading and unloading. The types and number of cracks in unloading specimen are much more complicated than uniaxial loading. (2) Judging from the type of cracks, shearing stress plays a leading role in the failure when uniaxial and biaxial loading. When unloading, the tensile stress plays a leading role especially in the pre-destruction stage. (3) The new parameter, MC, is used to define the effective shear stress (MC). According to its distribution near the crack tip, the dangerous azimuth and the area of initiation of new crack are determined. The experimental results show that the included angle with prefabricated crack is about -135 ° and 45 ° The left and right zones are the danger zones created by new cracks (bands). (4) When loading rock bridge through is caused by shear stress, when unloading is caused by the combination of tensile shear.