Abstract：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 carried out. On the basis of numbers of calculation results，the critical early warning value 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 of side walls of the eight projects and corresponding critical value 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.
