不同深度玄武岩的三点弯曲细观破坏实验研究

 现有深部岩石力学研究大多是从某一深度取出岩样，然后施加不同围压用于模拟不同深度，由此来研究不同深度情况下岩石的物理力学行为这一情况，然而实际中如果深度发生变化，不仅围压发生变化，岩石自身的微细观结构也会发生变化。针对此情况，选取北京门头沟一个有特点的区域，该区域从地表到深度1 100多米都有玄武岩。借助带加载装置扫描电镜(SEM)系统实时观察中心预制缺口不同深度玄武岩、偏心单裂纹及双裂纹玄武岩的细观破坏行为，揭示深度导致岩石力学性能变化的细观机制。研究发现，三点弯曲玄武岩试样中裂纹多数从预置缺口处萌生，进而发展成一条连续主裂纹。不同深度玄武岩的破坏荷载及断裂能随埋深呈增加趋势，主要原因是随着深度增加玄武岩更为致密，孔隙率小；相同偏心距下，偏心单、双2组试样峰值荷载和断裂能都几乎相同，且都随偏心距的增大而线性增加，主要原因是偏置裂纹试件缺口附近受到剪切力和弯矩的双重影响，但随着偏心距离的增加，弯矩影响在逐渐减少，这导致了峰值荷载和断裂能增加。

INVESTIGATION ON FAILURE BEHAVIOR OF BASALT FROM DIFFERENT DEPTHS BASED ON THREE-POINT BENDING MESO-EXPERIMENTS

Most of deep rock mechanics focus on rock samples from the same depth in the existing literatures. People hope to investigate the effects of different depths on mechanical behavior through applying different confining pressures on samples. In addition，the physico-mechanical behaviors of different depth rocks have been reported in many literatures. However，it is well known that both the confining pressure and rock microstructure will change with the increasing depth. In Mentougou district in Beijing，there is a special area，where from the surface to the depth of 1 100 meters，there is basically a same lithology，namely basalt. Scanning electron microscope(SEM) system with loading devices has been successfully employed to investigate the mesoscopic failure behavior of Mengtougou basalt with centric preset notch in different depths，offsetting single notch and double notches basalt. We hope to reveal mesoscopic mechanism of basalts with changing depths. Experimental results indicate that the crack will initiate from preset notch and develop into a continuous main crack for most of basalt samples in three-point bending tests. Both the failure load and the fracture energy for different depth basalts increase with the depth. The main reasons are that not only the microstructure of deep basalt is compact，but the porosity is smaller with the increasing depth. Both peak load and fracture energy of basalt with single preset notch are approximately same with those of double preset notches for the same offsetting distance. In addition，peak load and fracture energy will linearly increase with the increasing offsetting distance. The main reason is that though the failure of basalts with offsetting notch is affected by both of shear force and bending moment；and the bending moment gradually decreases with the increasing offsetting distance which induce the increase of peak load and fracture energy increase.