节理玄武岩体弹性波频散效应研究

DISPERSION EFFECT OF ELASTIC WAVE IN JOINTED BASALTS

以裂隙为例,将岩体裂隙作为内边界处理,构造符合内边界条件的格林函数,结合边界积分方法研究岩体内部裂纹、孔洞等不连续结构面对弹性波的散射。与室内试验结果和现场测试结果进行对比,结果表明:基于模型计算的波速与现场测试结果吻合较好,但与室内试验结果有较大差异。这种差异主要是室内试验和现场测试中岩体所处的应力状态、边界条件等因素的差别造成的。进一步探讨节理岩体的细观结构对频散效应的影响,结果表明随着裂隙长度的增加和孔隙度的增大,频散效应越显著;改变裂隙和入射弹性波相对方向,频散效应亦发生相应变化。其结果对现场声波和地震波的测试具有很好的指导意义。

The jointed basalt is a kind of complicated material with large numbers of complex structures such as micro-cracks, micro-holes at the meso scale, and with non-uniformity and non-continuity properties at the macro scale, which leads to complexity of propagation rules of elastic wave in them. The analytical method based on the continuity can not be used to fully deal with those. In the present paper, for the study of mesostructure of rock on the law of wave propagation, cracks are taken for example and treated as inner boundaries. Based on the Green＇s function method, considering the introduction of suitable inner boundary conditions, and combined with method of boundary integral, the scattering of elastic wave is studied. Wave velocities of elastic wave predicted by the dispersion equation are compared to the results of laboratory experimental and in-situ test results, which show that the theoretical results in the present model are consistent well with in-situ test results; however, there is a wide gap with the results of laboratory experiment, which may be due to the differences between the environment of indoor experiment and in-situ test such as the stress state of rock samples, temperature and other factors. Furthermore, the mesostructures factors of the jointed basalt influencing on the dispersion effect are discussed, which results that the dispersion effect is strengthened with the increase in porosity and crack length in a certain range; all those results are guidance for in-situ test of acoustic and seismic wave.