水力耦合下岩石的声发射特征试验研究

EXPERIMENTAL STUDY ON ACOUSTIC EMISSION CHARACTERISTICS OF ROCK CONCERNING HYDROMECHANICAL COUPLING

在单轴压缩条件下,分别讨论了4种岩石在考虑渗流和不考虑渗流条件下的声发射特征。研究表明:在低应力阶段,岩石几乎没有声发射活动,渗流对声发射活动无影响;一般在达到其强度的60%～80%左右、临近破坏时,声发射活动才显著增加;加渗流和卸渗流的瞬间均产生较大的声发射事件,从稳定渗流到卸渗流一般接收不到明显的声发射信号;岩体破坏的声发射过程分为4个部分,即初始区、剧烈区、下降区和沉寂区;在破坏时,声发射信号的主频分布较宽,其中不加渗流时低频成分所占的比例超过了50%,坚硬岩石主频的最大值较破坏前、后急剧增大;加渗流或长期浸泡(130h左右)时低频成分所占的比例超过了60%～80%,软化岩石主频的最大值较破坏前后变化不大;岩石的声发射主频与岩石的强度有关,强度越高,主频也越宽;随着应力的增加,有些岩石的声发射主频最大值有增大的趋势。

Acoustic emission（AE） tests are performed on rock samples under uniaxial compression with and without seepage flow, respectively; and four kinds of rock＇s AE characteristics are identified and analyzed. Results of the AE tests show that, at lower stress levels, almost no AE occurs in the rock and the seepage flow has little effect on AE activities. However, when the compressive stress reaches to the value of 60% - 80% of rock strength, the AE activities increase remarkably. Drastic AE events occur at the moment when the seepage flow is loaded or unloaded and almost no AE signals are able to be received when the seepage flow is unloaded in steady state. Rock breakage process can be divided into four phases according to its AE characteristics, that is, beginning phase, tempestuous phase, drop phase and dreary phase. During rock breakage, dominant frequency of rock AE is broader than that of intact rock, where the percentage of low frequencies exceeds 50% without seepage flow through the rock. Comparing the dominant frequency of hard rock＇s AE to those before and after its breakage, the maximal dominant frequency during breakage increases remarkably. However, the percentage of low frequencies exceeds 60% - 80% for rocks with seepage flow through them or marinated for a long time（about 130 h）, and the maximal dominant frequency of intenerated rock does not change significantly. Furthermore, the dominant frequency of rock AE varies with the rock strength; the larger the strength is, the broader the dominant frequency is. With the increase of the compressive stress, the maximal dominant frequency exhibits an increasing trend for some kinds of rocks.