循环剪切荷载作用下岩石节理变形特性试验研究

Experimental study of deformation behavior of rock joints under cyclic shear loading

以水泥砂浆为相似材料,制备3种岩壁强度、5种起伏角度的锯齿型节理试样;利用试验设备,进行了在4种法向应力下的循环剪切试验。根据试验结果,结合循环剪切试验特点,定义剪胀角来表征节理循环剪切的法向变形特性,以及剪切刚度来表征节理循环剪切的切向变形特性。基于不同起伏角、不同强度等级和不同法向应力下的节理试样循环剪切试验结果,分析了循环剪切过程中剪胀角和剪切刚度的变化规律;并利用不同条件下的试验结果,对比分析初始起伏角度、法向应力、岩壁强度对节理循环剪切变形特性的影响规律。研究发现:剪胀角、剪切刚度均随着剪切循环次数的增加而呈现先快、后慢的降低趋势,并且中低起伏角度节理的剪胀角、剪切刚度的降低趋势随着初始起伏角度、法向应力的增加而加快,随着岩壁强度增加而变慢,高起伏角度节理的剪胀角、剪切刚度的降低趋势基本保持不变。

Using cement-mortar as similar material, joint specimen with three joint wall strengths and five asperity angles are prepared. Then a series of cyclic shear tests are performed at four normal stresses on the cyclic shear test apparatus. Based on the test results and loading characteristics, the dilation angle and shear stiffness are defined. The normal deformation of joints under cyclic shear is characterized by dilation angle, and the tangential deformation is characterized by shear stiffness. Based on a variety of cyclic shear test results, the relationships between dilation angle and shear stiffness with shear cycles are analyzed. By comparing the results of different experimental conditions, the effects of initial asperity angles, joint wall strength and normal stress on the joint deformation properties are also analyzed. Research discovers that, the dilation angle and shear stiffness all appear a first quick back slow downward trend with the increase of cycle number. For the joint specimens with low and medium asperity angles, downward trend for dilation angle and shear stiffness shows an accelerating tendency with the increase of initial asperity angles and normal stress; but show a decelerating tendency with the increase of joint wall strengths. For the joint specimens with higher asperity angles, the downward trend for dilation angle and shear stiffness keep mainly unchanged.