围压对巷道围岩应力分布及松动圈的影响

Effect of Confining Pressure on Distributions of Horizontal and Vertical Stresses around Rectangular Roadway and Broken Rock Zone

使用FLAC模拟了巷道底板下方的一列单元(36个)不同围压时水平应力(与圆巷环向应力类似)及垂直应力(与径向应力类似)的分布规律。在峰值强度之前及之后,岩石的本构模型分别取为线弹性及莫尔库仑剪破坏与拉破坏复合的应变软化模型。水平应力是连续的,其峰值位于弹性区,这是由于单元在屈服之后,在叠代(为了达到平衡状态)过程中发生了应变软化。在塑性区,水平及垂直应力均是上凹的。当水平应力达到峰值之后,水平应力是上凹的,垂直应力是上凸的。距离巷道底板的距离越远,垂直应力越大。随着围压的增加,水平应力的峰值近似线性增加;垂直应力的峰值与围压的偏差增加,这意味着剪切应力也增加。当围压较低时,松动圈的外边界近似为圆形,应变软化区类似圆环。当围压较高时,松动圈的外边界为矩形,应变软化区为薄壁矩形。随着围压的增加,松动圈的厚度增大,而应变软化区的尺寸不改变。

Using FLAC, a column of thirty six elements closer to the vertically symmetric axis of plane strain model and below the floor of the roadway is monitored to obtain the distributions of horizontal stress （ similar to the hoop stress around a circular roadway） and the vertical stress （ similar to the radial stress） at different confining pressures. In elastic stage, the adopted constitutive relation of rock was linear elastic; in strain-softening stage, a composite Mohr-Coulomb criterion with tension cut-off and a post - peak linear constitutive relation were adopted. The horizontal stress is continuous and its peak falls into elastic zone since the yielded element undergoes strain-softening behavior in the process of iteration to achieve the equilibrium. The horizontal and vertical stresses are concave upward in plastic zone. When the horizontal stress reaches its peak, the horizontal stress is concave upward, while the vertical stress is convex upward. The vertical stress is higher at the place far from the roadway. The peak of horizontal stress linearly increases with confining pressure. At higher confining pressures, the difference between the peak of vertical stress and the confining pressure is apparent owing to higher tangential stress. At lower confining pressures, the external surface of broken rock zone （ BRZ ） around the rectangular roadway is like a circular and the strain-softening zone （SSZ） is like a cirque. At higher confining pressures, the external surface of BRZ is like a rectangle and SSZ is llke a thin-waUed rectangle. With increase of confining pressure, the thickness of BRZ increases. Confining pressure does not influence the thickness of SSZ.