Roof stability in deep rock tunnels
Roof stability in deep rock tunnels
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DOI：
10.1016/j.ijrmms.2019.104139
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发表时间：
2019-12-01
影响因子：
7.2
通讯作者：
Michalowski, Radoslaw L.
中科院分区：
文献类型：
--
作者：
Park, Dowon;Michalowski, Radoslaw L.
提出了一种基于极限分析运动学方法的隧道顶板稳定性定量评价方法。考虑了矩形(平顶)和圆形两种截面的长隧道。岩石受Hoek-Brown强度包络和正态流动规则的约束，并假定在破坏时提供足够的延性，从而使塑性定理适用。崩塌机制中的崩塌块体与静止的岩石之间有一条变形带将其与静止的岩石隔开，在其宽度上具有很大的速度梯度。根据机构的运动容许性要求和与相应的稳定性度量相一致的优化过程，确定了临界机构中块的形状。首先计算了隧道稳定所需的稳定数和支承压力。虽然在岩石工程中较少使用，但已发展出一种估算安全系数的方法，安全系数的定义是由Hoek-Brown准则确定的岩石剪切强度与强度要求的比率。奇怪的是，对于平顶隧道，这种安全系数的定义等于取决于单轴抗压强度和隧道尺寸的无量纲组与稳定数的比率。这种等效性不适用于具有有限曲率天花板的隧道。毫不奇怪，所有衡量隧道顶板稳定性的指标都强烈依赖于描述岩石质量的地质强度指数。
A method is presented addressing quantitative assessment of tunnel roof stability, based on the kinematic approach of limit analysis. Long tunnels with both rectangular (flat-ceiling) and circular cross-sections are considered. The rock is governed by the Hoek-Brown strength envelope and the normality flow rule, and it is assumed to provide enough ductility at failure, making plasticity theorems applicable. A failing block in the collapse mechanism is separated from the stationary rock by a deformation band with a large gradient of velocity across its width. The shape of the block in the critical mechanism is found from the requirement of the mechanism's kinematic admissibility and an optimization procedure consistent with respective measures of stability. The stability number and the supporting pressure needed for tunnel stability are calculated first. Although less commonly used in rock engineering, a procedure is developed for estimating the factor of safety, defined as the ratio of the rock shear strength determined from the Hoek-Brown criterion to the demand on the strength. Curiously, for flat-ceiling tunnels, such definition of the factor of safety yields results equivalent to the ratio of a dimensionless group dependent on the uniaxial compressive strength and the size of the tunnel to the stability number. Such an equivalency does not hold for tunnels with ceilings of finite curvature. Not surprisingly, all measures of tunnel roof stability are strongly dependent on the Geological Strength Index that describes the quality of the rock.