预静载与周期扰动荷载组合作用下花岗岩的断裂韧度与声发射特征

Fracture Toughness and Acoustic Emission of Granite Under Pre-static and Cyclic Loading

钻爆法是大型地下工程的主要开挖施工方法。对洞室围岩而言,除受地应力作用外(静载),还经常受到爆破等扰动荷载的作用。地应力与爆破扰动的耦合作用在深部高地应力条件下表现更为显著。因此,研究动静组合荷载作用下岩石的力学行为,特别是断裂特征,可为预测和控制深部岩石工程特有的问题提供理论基础。作者采用人字形切槽巴西圆盘(cracked chevron notched brazilian disc,CCNBD)试样,在MTS815 Flex Test GT岩石力学试验机上进行组合加载试验,研究花岗岩在预静载和周期扰动荷载组合作用下的断裂韧度与破坏特征。在获得静态断裂韧度的基础上,分别设定预静载为静态强度的50%、85%和90%,再分别施加50%、15%和10%的扰动荷载,获得组合加载条件下断裂韧度和声发射信号,分析Falicity比和声发射b值。结果表明:1)组合荷载作用下试样的裂纹张开位移(crack open displacement,COD)比静态加载时大,但随着预静载的增大而减小。2)花岗岩CCNBD试样的塑性变形比、修正断裂韧度均随预静载的增大而增大。3)预静载较低时,对试样承受扰动荷载能力的影响较小;预静载比达到90%后,试样对扰动荷载很敏感,且随着扰动荷载的施加,试样发生渐进破坏。

The drilling and blasting method is the major excavation method for large underground caverns. Except for the load from in-situ stresses（static）, the cavern rock mass will also bear the dynamic load frequently from blasting during excavation. The coupling effect of the insitu stress and the blasting-induced disturbance is more significant at depth where in-situ stresses are much higher. So the study on the rock behavior, especially its fracture characteristics under the coupling loads may provide a theoretical basis for the prediction and control of the specific problems of rock engineering at a great depth. In this paper, the cracked chevron notched Brazilian disc（CCNBD） specimens of granite were tested to investigate their fracture toughness and failure characteristics under coupled pre-static and cyclic load by MTS815 Flex Test GT testing system. The static strength or fracture toughness is first acquired, and then the pre-static load of the 50%, 85% and 90% of the static strength is set respectively and the other 50%, 15% and 10% of the static strength is further applied as cyclic disturbance load, thus to obtain the fracture toughness under coupled loading. All the acoustic emission（AE） signals are recorded in the tests, and Felicity ratio and b-value are analyzed. Results indicate that： 1） The crack opening displacement（COD） of the specimens under coupled load is larger than that under static load, but it decreases with the increase of pre-static load. 2） The plastic deformation ratio and corrected fracture toughness increases gradually with the increase of prestatic load. 3） Granite has better capability to withstand the cyclic disturbance load under lower pre-static load. When the pre-static load reaches90%, the capability drops greatly and the failure is progressive.