重复剪切作用下节理强度和形貌特征劣化规律

Degradation laws of joint strength and micro-morphology under repeated shear tests

为了分析重复剪切作用下节理面剪切力学特性及微观形貌特征劣化规律,制备了单节理砂岩试样,考虑4种法向应力分别进行了6次重复剪切试验。研究结果发现:(1)在重复剪切作用下,节理面剪应力–剪切变形曲线变化特征明显,经过2~3次剪切,不再出现明显峰值,剪切硬化现象明显,残余抗剪强度逐渐趋于稳定;(2)随着重复剪切次数增加,节理面的抗剪强度劣化趋势明显,呈先陡后缓的劣化趋势,前2次剪切的劣化幅度占总劣化值的65%以上,而且法向应力越大,抗剪强度劣化幅度和劣化速度越大;(3)在重复剪切作用下,节理面上相互咬合的微凸起和凹陷部分发生切齿、磨损和填充,节理面的凹凸起伏程度逐渐减小,使得其形貌特征参数及粗糙度系数逐渐降低,进而导致其剪切力学特性逐渐劣化;(4)建立了重复剪切作用下节理面粗糙度系数劣化方程,结合N.Barton提出的结构面抗剪强度经验公式,建立了考虑重复剪切作用的节理面抗剪强度计算公式,结果表明计算值与试验值吻合的较好。

In order to analyze the degradation laws of shear mechanics properties and micro-morphology of joint planes under repeated shear tests, single joint sandstone specimens are prepared and six times of repeated shear tests are carried out respectively considering four kinds of normal stresses. The results show that:(1) During the repeated shearing process, the shear stress-shear deformation curve changes obviously. After 2 or 3 times of shear tests, there is no obvious peak shear strength and the shear hardening phenomenon is obvious, and the residual shear strength is gradually stabilized.(2) With the increase times of repeated shearing, the shear strength of the joint planes are deteriorated obviously. The deterioration trend is fast in the first place and then become slow. The degradation rate of the first two times of shear tests is more than 65% of the total deterioration value. In addition, the greater the stress, the greater and fast the shear strength degradation rate.(3) Under the repeated shearing effect, the occlusive micro-embossment and depression begin to incise, wear and fill with each other on the joint plane, and the concavo-convex fluctuation of the joint plane gradually decreases, thus makes the morphological parameters and roughness coefficient gradually decrease, and then it leads to the gradual deterioration of shear mechanics properties.(4) The deterioration equation for roughness coefficient under repeated shearing is established. Combining with N. Barton’s empirical formula for shear strength of structural planes, the formula for calculating the shear strength considering the repeated shearing effect is established. The results show that the calculated values agree well with the experimental ones.