Liu Bo, Chen Yifan, Lin Hang, Cao Rihong, Zhang Shengwen
School of Resources and Safety Engineering, Central South University, Changsha 410083, China.
Materials (Basel). 2023 Jan 31;16(3):1233. doi: 10.3390/ma16031233.
As a composite material, the stability of rock mass is usually controlled by a joint. During the process of excavation, the normal stress of the joint decreases continuously, and then the shear strength of the joint decreases, which may eventually lead to the instability and failure of rock mass. Previous studies have mainly focused on the shear behavior of joints under constant normal stress, but have rarely considered the unloading of normal stress. In this paper, a direct shear test of joints with different roughness was carried out, in which the shear stress remained unchanged while the normal stress decreased. The strength characteristics of joints were explored, and the deformation and acoustic emission-counting characteristics of joints were analyzed by digital image correlation (DIC) techniques and acoustic emission (AE). A new method for predicting the instability of joints under normal unloading was proposed based on the evolution law of normal deformation energy (U), tangential deformation energy (U) and total deformation energy (U). The results show the following: (1) The unloading amount of normal stress was enlarged for greater initial normal stress and roughness, while it decreased with an increase in initial shear stress. (2) AE events reached their maximum when the normal stress was equal to the failure normal stress, and the -value fluctuated more frequently in stable development periods under normal unloading conditions. (3) U would change with the loading and unloading of stress, and this may be used to predict the unloading instability of rock mass using the abrupt change of U.
作为一种复合材料，岩体的稳定性通常受节理控制。在开挖过程中，节理的法向应力不断减小，进而节理的抗剪强度降低，最终可能导致岩体失稳破坏。以往的研究主要集中在恒定法向应力下节理的剪切行为，而很少考虑法向应力的卸荷情况。本文进行了不同粗糙度节理的直剪试验，试验过程中法向应力减小而剪应力保持不变。探讨了节理的强度特性，并采用数字图像相关（DIC）技术和声发射（AE）分析了节理的变形和声发射计数特性。基于法向变形能（U）、切向变形能（U）和总变形能（U）的演化规律，提出了一种预测法向卸荷条件下节理失稳的新方法。结果表明：（1）法向应力卸荷量随初始法向应力和粗糙度的增大而增大，随初始剪应力的增大而减小。（2）法向应力等于破坏法向应力时声发射事件达到最大值，在法向卸荷条件下稳定发展阶段b值波动更为频繁。（3）U会随应力的加卸荷而变化，利用U的突变可用于预测岩体的卸荷失稳。
