The purpose of this paper is to solve the problem that deep and close-distance cavern and roadway group were easily affected by the adjacent chamber or roadway excavation disturbance and low stability and significant deformation of surrounding rock occurred. The stability and control technology of surrounding rock in the main shaft and auxiliary shaft system has been analyzed by the adjacent chamber and roadway group of −850 m level in Qujiang Mine, China, as an engineering background. Firstly, the numerical calculation of the excavation chamber was, respectively, carried out in different ways with the propagation theory of the excavation disturbance wave. The results show that the interaction of adjacent chamber excavation was more intense. When excavated at the same time, there is a large increase in the movement of the sides and the roof-floor of the chamber and roadway. Then, the mechanism of interaction between low-high stress and excavation disturbance was considered, the corresponding control principles were provided, and a set of critical technologies and equipment were designed according to the deformation characteristics of the large deformation soft surrounding rock. Finally, the comprehensive control method was put forward with the water pump house as an example, that is, anchor, metal net, grouting, combined anchor cable and large-diameter anchor cable. And the related support parameters were determined by the internal damage of the surrounding rock chamber. The numerical simulation results show that the surrounding rock deformation of the chamber and roadway reduced with the revised support program, which the expansion of the rock mass loose circle prevented effectively. The site test shows that the convergence rate of surrounding rock with the improved support was less than 0.2 mm/d, and the rock deformation of chamber and roadway suppressed significantly.
The selection of the support scheme for deep-buried and large-span chambers has been a severe problem in underground engineering. To further study the mechanical mechanism of large deformation, based on the repair engineering of the chambers of Pingdingshan No.6 mine in China, the field investigation, laboratory test, numerical simulation, and theoretical analysis were studied. The surrounding rock of the central substation chamber (CSC) and the main pumping chamber (MPC) were classified according to the rock mass rating (RMR) classification method, and the main factors affecting the stability of the surrounding rock of the chambers were revealed. A prediction model of mechanical parameters of the surrounding rock was established based on the Hoek-Brown failure criterion. Additionally, the prediction results were used in FLAC3D to further analyze the failure of the original support scheme, and the feasibility of the restoration plan was proposed. Six key points of support technology for this kind of chamber were put forward. Comprehensive support and repair scheme, including “bolt, metal mesh, shotcrete, grouting, anchor cable, and combined anchor cable,” was put forward. The engineering practice indicated that the deformation rate was less than 0.7 mm/d, which was beneficial to the long-term stability of CSC and MPC. The implementation of this restoration project can provide a reference for other similar projects.
After a gas drainage event causes different degrees of initial porosity in the coal seam, the heterogeneity of the coal mass becomes much more obvious. In this paper, soft coal testing samples with different degrees of heterogeneity were prepared first by a new special experimental research method using hydrogen peroxide in an alkaline medium to generate oxygen. Then, a series of mechanical tests on the soft coal mass samples were carried out under multiple factor coupling conditions of different heterogeneities and confining pressures. The results show that with a low strength, the ductility failure characteristic and a kind of rheology similar to that for soft rock flow were reflected for the soft coal; i.e., the stress-strain curve of the coal mass had no apparent peak strain and residual strength. An interesting phenomenon was found in the test process: there was an upwardly convex critical phase, called the brittle-ductile failure transition critical phase, for the heterogeneous soft coal mass between the initial elastic compression phase and the ductile failure transition phase in the stress-strain curve of the coal mass. An evolution of the brittle-ductile modulus coefficient of the soft coal was developed to analyze the effect of the internal factor (degree of heterogeneity) and external factors (confining pressure) on the transition state of the brittle-ductile failure of soft coal. Further analysis shows that the internal factor (heterogeneity) was also one of the essential factors causing the brittle-ductile transition of soft coal.
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