巷道开挖应力旋转路径下弱胶结软岩剪应力–应变及非共轴特性研究

The shear stress strain characteristics of weakly cemented soft rock under roadway excavation stress path and its non-coaxial characteristics

为探究巷道开挖引起的主应力旋转路径演化规律及其诱发的岩体变形问题,以弱胶结软岩巷道为工程背景,建立弱胶结软岩巷道开挖扰动数值计算模型,研究巷道开挖诱发的围岩主应力大小和方向演化规律,确定开挖扰动旋转应力路径试验加载状态参数。开展弱胶结软岩空心扭剪试验,研究9种开挖扰动应力旋转路径下弱胶结软岩剪应力–应变–掘进距离空间曲线特征及(σ_(z)-σ_(θ))-2τ_(zθ)应力平面内的非共轴角变化规律。结果表明:随着巷道开挖,监测面位置巷道围岩底板、顶板和两帮的主应力大小和方向均发生显著变化,特别是在巷道2D范围内,发生了强烈的主应力方向旋转和应力量值突变。开挖扰动应力路径下巷道围岩剪应力–应变曲线呈现“V”,“Z”,“N”型发展形式。开挖扰动引起的主应力旋转造成了弱胶结软岩应变增量方向和应力方向的非共轴性,巷道底板、顶板和两帮扰动应力路径作用下,弱胶结软岩非共轴角最大值分别为52.8°,-22.3°和30.6°。研究成果将有助于揭示巷道开挖卸荷引起的主应力旋转路径下岩体非共轴塑性变形演化机制,提高地下工程设计水平以及灾害防治能力。

To investigate the evolution law of principal stress rotation path caused by tunnel excavation and the resulting deformation in rock masses,a numerical model has been developed to explore the evolution of principal stress rotation paths and resultant rock mass deformations due to tunnel excavation,with a focus on weakly cemented soft rock tunnels.This model examines the changes in magnitude and direction of principal stresses surrounding the tunnel,induced by the excavation process.Parameters for loading states in excavation-disturbed rotational stress path experiments are determined through this investigation.Nine kinds of excavation disturbance stress rotation paths tests were conduct by using hollow torsional shear tests on weakly cemented soft rock.The spatial curve characteristics of shear stress-strain excavation distance law and non-coaxial angle variation in the stress(σ_(z)-σ_(θ))-2τ_(zθ)plane was researched.Significant changes were observed in the magnitude and direction of principal stresses in the surrounding rock of the tunnel,including its floor,roof,and sidewalls,as excavation progressed.Particularly within the 2D range of the tunnel,strong stress rotation and abrupt stress magnitude changes occurred.Shear stressstrain curves at monitoring points in the surrounding rock,influenced by excavation disturbance stress,were observed to develop in patterns resembling V,Z or N shapes.Excavation disturbance in weakly cemented soft rock induced principal stress rotation,resulting in a non-coaxial angle between strain increment and stress directions.The non-coaxial angles peaked at 52.8°,-22.3°and 30.6°for the tunnel floor,roof and sidewalls,respectively,influenced by stress path variations.This research results light on the non-coaxial plastic deformation in rock masses,a result of principal stress rotation from tunnel excavation.The design level and disaster prevention capability of underground engineering are enhanced.