微扰动作用下预静载硬岩的断裂特性研究

Study of hard rock fracture properties with pre-static load under micro disturbance

为了研究预静载条件下硬岩在微扰动作用下的断裂特性变化规律,采用花岗岩制作中心直裂纹巴西圆盘(CSTBD)试样,在MTS Landmark电液伺服试验机上,利用圆弧形加载方式,进行硬岩在平行于预制裂纹方向的预静载荷和微扰动载荷的组合作用下的断裂特性研究。设定预静载荷水平为常规准静态断裂载荷的90%,设定微扰动载荷幅值为常规断裂载荷值的10%,下限为常规断裂载荷的80%,上限为常规断裂载荷值。扰动频率分别为1 Hz、5 Hz、10 Hz、20 Hz、30 Hz、50 Hz和70 Hz。研究结果表明:在预静载加载段,岩石试样内部沿预制裂纹方向新的裂纹已经产生发展,并且裂纹扩展的速度随着载荷的增大而增大;在扰动载荷加载段,随着扰动次数的增加,裂纹扩展的速度越来越慢,岩石损伤程度逐渐积累;在断裂破坏段,岩石损伤程度超过了承受极限,裂纹贯穿沿预制裂纹方向贯穿试样,岩石断裂破坏;在预静载作用下,试样已经处于临界失稳状态,扰动作用会诱发试样的断裂失稳破坏,扰动频率超过10 Hz后,减韧效应随着扰动频率的提高并不明显,扰动使得试样的总体变形量有减小的趋势。

In order to study the change rules of hard rock fracture properties with pre-static load under micro disturbances,CSTBD samples prepared with granite are used to study the fracture properties under the combined influence from pre-static load and micro disturbance parallel to the prefabricated crack in the MTS Landmark electro hydraulic servo testing machine by the manner of circular loading. The pre-static load level is at set 90 % of the normal static fracture load strength,the micro disturbance load is set at 10 % of the normal strength while the minimum limit is set at 80 % of the normal strength and the maximum limit is set at the full strength. The disturbance frequencies are1 Hz,5 Hz,10 Hz,20 Hz,30 Hz,50 Hz and 70 Hz. The study results show that in the pre-static load loading phase,new cracks have occurred and developed along the direction of the prefabricated crack inside the rock sample and the crack propagation rate increases with the load increase; in disturbance load loading phase,crack propagation speed becomes slower and slower and rock damage degree gradually accumulates with the increase of disturbance frequency;in fracturing phase,rock is damaged beyond limit,crack forms across the sample and the rock fractures; with pre-static load,the sample is at critical state of instability which will be induced by disturbance,and when disturbance frequency exceeds 10 Hz,the toughness reduction effect is not evidently enhanced with the increase of disturbance frequency and disturbance makes the overall deformation of the sample tend to decrease.