论文部分内容阅读
裂缝的演化与空间展布规律是影响泥岩盖层密闭效果的关键因素。为研究泥岩失稳破坏过程中裂纹的萌生、扩展和汇集贯通等演化规律,针对龙马溪组泥岩进行了单轴压缩下的同步CT扫描试验,通过裂纹面积的变化特征及裂纹结构的分形特性,探讨了不同加载水平下裂纹的演化规律,从细观尺度揭示了泥岩裂纹演化与宏观变形特性的关系。研究结果表明:泥岩CT图像灰度频率及裂纹面积的变化均可反映裂纹的演化特征。荷载水平(即当前荷载与峰值荷载之比)为0~20%时,裂纹面积迅速增加,裂纹开始萌生,但由于受到闭合效应的抑制,相对并不活跃;荷载水平(当前荷载与峰值荷载之比)为20%~65%时,裂纹面积变化不大,裂纹萌生效应和闭合效应同时进行,且作用大致相抵,泥岩进入稳定承压阶段;荷载水平为65%~85%时,裂纹面积陡然增加,裂纹进入扩展及汇集贯通阶段,而荷载水平为65%时的突然跳跃,表明裂纹从萌生闭合到扩展过渡具有突发性和瞬时性。随着荷载的继续增加,泥岩内部结构呈复杂化、混乱化的变化趋势,且裂纹从外向内逐渐贯通。裂纹分形维数呈现的增长―下降―再增长―再下降的波状变化规律,是裂纹萌生、闭合、扩展和归并等相互转化的结果。
The evolution of fractures and the law of spatial distribution are the key factors that affect the sealing effect of mudstone caprock. In order to study the evolution of crack initiation, propagation and coalescence in the process of instability of mudstone, a synchrotron CT scanning experiment was carried out on the mudstone of Longmaxi Formation under uniaxial compression. According to the variation of crack area and the fractal characteristics of crack structure, The evolution of cracks under different loading levels was discussed. The relationship between the evolution of cracked mudstone and macro-deformation was revealed from the meso-scale. The results show that both the gray frequency of CT images and the change of crack area reflect the evolution of cracks. When the load level (ie, the ratio of current load to peak load) is 0-20%, the crack area increases rapidly and the crack initiation begins. However, the crack initiation is relatively inactive due to the suppression of the closure effect. The load level (current load vs. peak load The ratio of cracks is small, the crack initiation and closure effects occur at the same time, and the effect is roughly offset, and the mudstone enters the stable pressure stage. When the loading level is 65% -85%, the crack area is abrupt Increase, the crack enters into the expansion and pooling through stage, and the sudden jump when the load level is 65%, which shows that the crack has the characteristics of suddenness and instantaneous transition from initiation to expansion. With the increase of load, the internal structure of mudstone shows a complex and chaotic trend, and the cracks gradually penetrate from the outside to the inside. Crack fractal dimension presented growth-decline-re-growth-and then decline of the wavy changes, the crack initiation, closure, expansion and merger and other mutual transformation results.