Mine-by试验洞开挖过程中围岩应力路径与破坏模式分析

Analysis of stress path and failure mode of surrounding rock during Mine-by test tunnel excavation

地下洞室开挖过程中,围岩经历了复杂的应力路径,正确刻画围岩的应力路径及其影响是岩石地下工程中亟待解决的关键科学问题。基于起裂判据(CIC)、扰动应力比(n=σ_3/σ_1)和Lode参数等力学表征指标,采用FLAC^(3D)对Mine-by试验洞掌子面掘进过程中围岩的复杂应力路径和破坏模式进行探讨。研究表明:围岩应力场的扰动主要集中在掌子面前后一倍洞径范围内,围岩损伤受掌子面附近高度集中的偏应力和应力主轴旋转支配;随掌子面掘进,围岩顶部和底部偏应力集中程度加大,应力比n逐渐降低,逐步形成V型剥落,而隧洞边墙部位逐渐卸荷,损伤破裂转变为拉应力控制;原位岩体的应力路径涉及应力主轴旋转效应,远比实验室的单调加载路径复杂,Mine-by试验洞开挖过程中,在掌子面的顶部和底部,围岩大主应力方向几乎没有转动,而中主应力和小主应力旋转一定角度(35.2°)后回到初始方向,由于中主应力超过了岩体起裂强度(CIC>1),其方向的旋转加剧了围岩的损伤程度。相关认识和结论具有一定的理论和工程意义。

During the underground excavation, the stresses in surrounding rock follow the complex paths. It is a key issue to describe the stress path and its effect on the surrounding rock correctly in underground engineering. The complex stress paths and failure modes of surrounding rock during Mine-by test tunnel excavation are discussed based on three parameters including the crack initial criterion（C/C）, the stress ratio n = σ3/σ1 and the lode parameter. It is shown that the disturbance of stress field is mainly concentrated near the excavation face within the scope of the tunnel diameter and the damage of surrounding rock is controlled by the highlyconcentrated deviatoric stress and stress axis rotation. As the excavation face advances, the deviatoric stress concentration increases and the stress ratio reduces at the top and the bottom of the surrounding rock, where a v-shaped spalling has been formed gradually. The surrounding rock of the tunnel wall unloads gradually, and the damage is changed to be controlled by the tensile stress. The stress path of in-situ rock is more complex than that in laboratory because of the effect of stress rotation. During the excavation of Mine-by test tunnel, the rotation of the major principal stress direction is hardly changed at the top and the bottom of surrounding rock, and the intermediate principal stress and minor principal stress rotate 35.2 degrees before returning to the initial direction. Since the intermediate principal stress has exceeded the rock mass crack initiation strength（CIC〉 1）, the stress rotation aggravates the damage degree of surrounding rock.