砂岩卸围压变形过程中渗透特性与声发射试验研究

 利用岩石伺服试验系统，对江西红砂岩岩样进行气体渗透三轴试验及声发射监测，研究在常规加载、峰前卸围压和峰后卸围压3种应力路径下，岩样变形破坏过程中的渗透规律和声发射特征。试验结果表明：(1) 随着有效围压的增大，岩石岩样的应力峰值逐渐增大，岩样的应力峰值对有效围压很敏感。(2) 常规加载时，渗透率在岩石屈服前呈现略微下降的趋势，屈服后迅速增长，峰后应变软化阶段有小幅回落；峰前和峰后卸围压时，在卸载之前渗透规律与常规加载时相同，卸载后渗透率均呈急剧增长的趋势，增幅也较大，其中峰前卸围压后渗透率增幅最大。(3) 在相同加载方式下，围压的增大不影响渗透率曲线的发展趋势，只影响渗透率在各阶段量值的大小。(4) 常规加载时，岩石声发射活动在屈服前比较平静，屈服后声发射活动非常活跃，峰后应变软化阶段声发射活动再次趋于平静；峰前卸围压不久后，声发射活动异常活跃、密集，能量数相对值较大并有明显峰值；峰后卸围压过程与常规加载过程中声发射规律相似。(5) 岩样的破坏过程中，随围压增大，脆性减弱、延性增强，在同一围压水平下，峰前卸围压破碎程度最高，脆性最强。(6) 岩石扩容点与渗透率最小值所对应的轴向应变值十分接近，体应变和渗透率随轴向应变的变化趋势对应较好，声发射活动的密集阶段均发生在体积膨胀之后，渗透率、声发射、应力及(体)应变之间存在一定对应关系。

EXPERIMENTAL STUDY OF PERMEABILITY AND ACOUSTIC EMISSION CHARACTERISTICS OF SANDSTONE DURING PROCESSES OF UNLOADING CONFINING PRESSURE AND DEFORMATION

Triaxial compression tests and acoustic emission(AE) monitoring were carried out for Jiangxi red sandstone using servo-controlled rock mechanical test system；its permeability was tested with gas at the same time. The rock permeability rules and AE characteristics under the failure processes of three types of stress paths，i.e. conventional triaxial compression，unloading confining pressure at the pre-peak and post-peak strength，were studied. The experimental results indicate that：(1) The peak strength of rock samples increases gradually with the increase of effective confining pressure，which means that the peak strength is sensitive to effective confining pressure. (2) In conventional triaxial compression test，the permeability curves fall slightly before yield and then increase dramatically after yield and suffer a slight pullback at the post-peak strain softening stage. The permeability trends before unloading of confining pressure at the pre-peak and post-peak strength are basically the same as that under conventional triaxial compression process. The curves both grow more rapidly after unloading. (3) Under the same loading path，changes of confining pressure only affect the relative values of permeability during all stages，but not affect the trends of the curves. (4) In conventional triaxial compression test，AE activity is relatively quiet prior to yield，and begins to liven up after yield then tends to be quiet again at the post-peak strain softening stage. Shortly after unloading of confining pressure at the pre-peak strength，AE activity appears extremely active and dense. The strength of signal is relative higher and reaches an obvious peak value. The AE law in the test process of unloading confining pressure at the post-peak strength is similar to that in the process of conventional triaxial compression test. (5) With the increase of confining pressure，rock appears more ductility and less brittleness in failure process. At the same confining pressure，rock presents most brittleness and reaches highest broken degree. (6) The dilatancy points of rock samples are close to the minimums of permeability. There is a well corresponding between volumetric strain and permeability with axial strain. The intensive stages of AE activity emerge after dilatancy. It is shown that there are some links among permeability，AE，stress and (volumetric) strain.