花岗岩声发射特性和破坏机制的实验研究

EXPERIMENTAL RESEARCH OF THE AE CHARACTERISTICS AND FAILURE MECHANISM OF A GRANITE

本文针对洞壁围岩支护前后的应力状态,对花岗岩的声发射特性和破坏机制进行了实验研究.指出:在σ_2≤15.5 MPa,σ_3≤0.5MPa的条件下,双轴及三轴压缩强度无明显提高,可用单轴压缩强度作为其代表值.和单轴压缩相比,低侧压改变了花岗岩的破坏模式,使破坏向三轴压缩下的“亚破碎型”转化. 对比分析花岗岩块的强度、变形和声发射特征后,提出了“脆性破坏警报线η”,“脆性破坏线β”,“极限破坏线”等表征花岗岩块变形发展及破坏过程的概念,给出了相应的临界应力条件,并用图4表示了不同破坏状态下的强度准则. 把花岗岩块的拉应变发展及不同破坏状态与Russense的岩爆分级表作了对比;结合实测地应力资料,对某地区圆形洞室的脆性破坏与岩爆活动作了粗略评估,认为考虑非圆形洞室几何因素所产生的应力集中及其它因素后,发生弱岩爆是可能的.评估结果和现场试验洞的情况以及挪威峽谷地区Heggura公路隧洞的现场经验较为一致.

According to the ground stress level of a project in China and the stress states in the cavern wall before and after supporting, the AE characteristics and failure mechanism of a granite from the site of that project have been studied experimentally. The results show that biaxial and triaxial compressions with σ_2≤15.5 MPa and σ_3≤0.5 MPa do not increase rock strength significantly and thus the uniaxial compressive strength of rock can be used in place of its biaxial and triaxial strengths. In comparison with uniaxial compression, a low lateral pressure or constraint can make the mode of failure of the granite transform towards a 'sub-clastic mode' under triaxial compression. Based on comparisons of the strength, deformation andAE characteristics of this granite, this paper has presented the concepts of the 'limit line for brittle fracture warning', the 'limit line for brittle rupture' and the 'limit line for ultimate failure' etc. which can characterize the strain development and the failure process. In addition, the critical stress conditions corresponding to various rupture states have also been given in Fig. 4 in the paper. The evolution of tensile strain and different rupture states of the studied granite are compared with Russense rockburst classification. On such a basis, the brittle rupture and rockburst activity of a circular cavern in a project in China are evaluated in accordance with the ground stress values actually measured there. It is believed that the first class rockburst, i. e., weak rockburst activity, is possible. This evaluation is fairly consistent with the actual situation in a test adit of that project and with the field experience of Heggurahigh way tunnel in the Norway Canyon region.