大型洞室群高边墙位移预测和围岩稳定性判别方法

STUDY ON PREDICTION OF HIGH WALL DISPLACEMENT AND STABILITY JUDGING METHOD OF SURROUNDING ROCK FOR LARGE CAVERN GROUPS

以二滩地下厂房群的结构形式为主要背景,考虑4种基本因素,经过大量的数值分析算例,拟合出一个可预测地下厂房高边墙关键点位移的推算式。所考虑的基本因素为岩体变形模量、洞室埋深、主厂房高度和水平初始地应力测压系数。在岩体参数中已隐含着配套的岩体强度参数。首先,采用国际上通用的FLAC3D软件进行准三维大量围岩稳定性分析计算,通过拟合得到预测位移的推算式为二阶代数方程,可迅速推算出边墙关键点的弹塑性和弹性位移值。然后,对国内已建成或在建的8个地下工程运用该推算式对关键点的位移值进行推算,并将结果和这些工程的数值分析值进行对比。结果表明,二者相符较好,从而说明该推算式的有效性。之后,又提出3种用于判定围岩稳定性的方法。建议采用普适性较好的弹塑性位移和弹性位移的比值判别方法。运用该判别方法对上述8个地下工程的围岩稳定性状态进行判断。同时,在大量算例总结基础上,对不同埋深给出相对位移比θ的临界预警值θc,并拟合出临界预警值随埋深变化的线性方程式。在考虑一定的安全系数后,将上述8个地下工程边墙位移比kθ与相应的临界预警值θc进行对比。最后,认为该8个地下工程中有4个稳定性差,建议需考虑施加长锚索加固以保证工程的稳定性。从该4个地下工程的实际设计来看,这些地下工程都已采用长锚索加固高边墙的方案,说明所提出的判别方法是有效的。

Taking the structural form of underground opening group of Ertan Project as the major background, and considering four basic factors, an expression that can predict the displacements of the key points on the high side walls of the underground houses is proposed through a great number of numerical analysis. Those basic factors include the deformation moduli of rocks, buried depths of openings, heights of major houses and lateral pressure coefficient of initial horizontal geostress component. The rock mass parameters have the implication of the matched strength indices of rock mass. The commonly used FLAC3D software is employed to conduct a great number of quasi 3D calculations about rocks stability. Using the second-order algebraic equations obtained through fitting that can predict displacements of high wall, both elastoplastic and elastic displacements of the key points on the side walls can be obtained rapidly. Then, the paper uses the above-mentioned equations to calculate the displacements of the key points of eight underground projects that have been completed or are being under construction or designing. Meanwhile, the calculation results are compared with the values from numerical analysis performed by former authors. The results show a good accordance between them, which indicates the effective nature of the above equations. Afterwards, three methods to judge whether surrounding rocks are stable, are put forward. The paper suggests that more commonly applicable method in-between them-the ratio of elastoplatic and elastic displacements is introduced as the main judging criterion. By using this criterion, the judgment on above-mentioned eight projects＇ surrounding rocks stability is carded out. On the basis of numbers of calculation results, the critical early warning value θc of the specific value of the above displacement ratio at different depths is given; and the linear equation to describe the relation between critical value and depth is also fitted. Considering a certain safety factor, the comparisons between the displacement ratio kO of side walls of the eight projects and corresponding critical value θc are made. Finally, the paper points out that the four projects among those eight are somewhat instable. So it is suggested that long cables should be used to reinforce the surrounding rocks to ensure the stability of these four projects. As a matter of fact, those four projects have introduced the reinforcing scheme by prestressed cables to support their high side walls already, showing that the proposed judging criterion is effective.