黏土半巷道围岩模型过巷道轴线平面破坏过程实验观测

Experimental Observation of Failure Processes of Clay Semi-models of the Tunnel Surrounding Rock at the Plane Going Through the Tunnel Axis

为了观测过巷道轴线平面上应变局部化带及裂纹的发展演化规律,开展了黏土半巷道围岩模型三轴压缩实验研究。半巷道围岩模型的观测表面处于平面应变状态,且分步开挖巷道。在每次巷道开挖之前,对半巷道围岩模型卸荷。每次巷道开挖之后,再对半巷道围岩模型加荷。采用数字图像相关方法观测了观测表面的最大剪切应变场,并统计了裂纹面积百分比随纵向应变的演化规律。得到以下结论:当纵向应变较高时,在半巷道围岩模型的观测表面上,出现了由巷道两帮或两帮与掌子面交点处发展出的应变局部化带;另外,还出现了距离巷道表面较远的应变局部化带。由此可以推出,垂直于巷道轴线平面上将会出现分区破裂化。裂纹面积百分比随纵向应变的增加而增加;随着阈值(可识别的裂纹面积的最小值)的增加,裂纹面积百分比降低,但降低的速度越来越慢。剪裂纹主要位于巷道的两帮;拉裂纹遍布各处,呈现一定的等间距性。

To observe the evolution of strain localization bands and cracks of the tunnel surrounding rock at the plane going through the tunnel axis,experimental studies of clay semi-models of the tunnel surrounding rock in triaxial compression have been conducted. The measured surface of the semi-model was in a plane strain condition and the tunnel was excavated in stages. Before an excavation step,the semi-model was unloaded. After an excavation step,the semi-model was reloaded. The maximum shear strain of the measured surface was obtained by use of the digital image correlation method. The statistical analysis of percentages of cracking areas with an increase of longitudinal strain was conducted. The results show that when the longitudinal strain reached a certain value,strain localization bands originated from both sides of the tunnel or originated from intersection points of two sides of the tunnel. In addition,some strain localization bands far away from the tunnel surface were observed. Therefore,the zonal disintegration of the tunnel surrounding rock at planes orthogonal to the tunnel axis would emerge. Percentages of cracking areas increased with an increase of longitudinal strain. With an increase of the threshold value(the minimum identifiable cracking area),percentages of the cracking areas decreased,and the decreasing velocity slowed down. Shear cracks were located mainly at both sides of the tunnel,while tensile cracks were scattered,whose spacing was approximately identical to some extent.