节理剪切过程中两翼微凸体接触规律及剪应力模型研究

Contact law of two wing asperities in the process of joint shear and shear stress model

为了探究节理剪切过程中微凸体接触规律,对张拉型节理面进行了三维扫描与直剪试验。通过三维点云追踪技术对节理面剪切过程中微凸体接触面积和接触角度进行了统计分析,基于微凸体接触规律建立了剪应力模型。在此过程中,得到如下结论:(1)剪切过程中,随着剪切位移的增大,接触面积逐渐减小,接触点由散落式分布转化为集中式分布,单个接触点面积逐渐增大,接触点数量逐渐减少,法向应力对接触面积影响显著,法向应力越大,接触面积越大。(2)在剪应力峰值前,上部岩块中大多数相互接触的微凸体处于“爬坡”状态,在剪应力峰值以后出现部分接触微凸体处于“背离”状态。剪应力峰值以前绝大多数接触的微凸体能够提供阻抗剪切的力,而在峰后存在部分微凸体无法提供阻抗剪切的力。(3)接触角近似呈现正态分布,随着剪切位移的增大,接触角的平均值呈现先增大后减小的规律。(4)对模型进行验证,结果表明,模型不仅能够描述不同法向应力条件下节理面的抗剪强度,而且能够反映剪应力-剪切位移的关系,证明了模型的合理性,为准确预测节理面抗剪强度提供了一种新的计算方法。

In order to explore the contact law of asperities in the joint during shearing process, three-dimensional scanning and direct shear tests were carried out on the tensile joint surface. The contact area and contact angle of asperities in the joint surface shearing process were analyzed by 3D point cloud tracking technology, and a shear stress model was established based on the contact law of asperities. In this process, the following conclusions were obtained: 1) In the shear process, with the increase of shear displacement,the contact area gradually decreases, and the contact points change from scattered distribution to centralized distribution. The area of a single contact point gradually increases, and the number of contact points gradually decreases. Normal stress has a significant impact on the contact area. The larger the normal stress, the larger the contact area. 2) Before the peak value of shear stress, most of the contacting asperities in the upper rock block are in a “climbing” state, and after the peak value of shear stress, some contacting asperities are in a “deviating” state. Before the peak of shear stress, most of the asperities contacted can provide shear resistance,while after the peak, some asperities cannot provide shear resistance. 3) The contact angle approximately presents a normal distribution and the average contact angle first increases and then decreases with the increase of shear displacement. 4) The verification results of the model in this paper show that the model can not only describe the shear strength of joint surface under different normal stress conditions, but also reflect the relationship between shear stress and shear displacement, which proves the rationality of the model. The model in this paper provides a new calculation method for accurately predicting the shear strength of joint surface.