Abstract
In this study, based on the mining of the 13210 working face in the Yima coal mine of the Gengcun village, China, a simplified mechanical model for the analysis of dynamic destabilization of the overlying strata during underground mining was constructed. The numerical simulation was used to analyze the stress patterns in the advanced abutments of the tunnel face and the characteristics of dynamic failures in the overlying strata. Furthermore, similitude experiments were conducted to study the process of stress release and deformation in the overlying strata, and to analyze the effects of overburden destabilization on the ground surface settlement. The theoretical analysis indicated that if the geometric parameters of a working face are fully determined, a stiffness ratio no greater than 1 is required for dynamic destabilization to occur. The numerical simulation results show that the stress in the overlying strata decreases with a decrease in distance from the tunnel face. The stresses in the advanced abutments initially increase with an increase in distance from the tunnel face, followed by a decrease in stress, and an eventual stabilization of the stress levels; this corresponds to the existence of a “stress build-up zone,” “stress reduction zone,” and “native rock stress zone.” In similitude experiments, it was observed that a “pseudoplastic beam” state arises after the local stresses of the overlying strata have been completely released, and the “trapezoidal” fractures begin to form at stress concentrations. If the excavation of the working face continues to progress, the area of collapse expands upward, thereby increasing the areas of the fracture and densification zones. Owing to the nonuniform settlement of the overlying strata and the continuous development of bed-separating cracks, secondary fractures will be generated on both sides of the working face, which increase the severity of the ground surface settlement.
Highlights
In recent years, problems caused by underground mining, such as surface subsidence, rock burst failures in the working face, and overlying strata fractures, have become increasingly prominent [1]
Ese research works generally include theoretical analyses, numerical calculations, and experimental studies. e theoretical studies on mining subsidence helped develop the masonry beam theory [2], key strata theory [3, 4], and supporting plate theory [5]. e numerical approaches may be generally divided into two categories. e first category pertains to methods based on continuum mechanics, for example, the finite element method (FEM), finite difference method (FDM), boundary element method (BEM), and element-free method (EFM). e second category of methods is based on discontinuum mechanics, which includes the discrete element method (DEM) and discontinuous deformation analysis (DDA) [6,7,8]
The FEM and FDM are highly effective methods for simulating the properties of a material in continuum states. These methods are incapable of simulating the process in which a material changes from a continuous to discontinuous state, and they cannot reveal the dynamics of a material in a discontinuous state. e block-discrete element method (B-DEM) and granular DEM have certain advantages in the simulation of noncontinuum dynamics; it is still difficult to simulate the continuous deformation processes of a material using these methods [9]
Summary
Problems caused by underground mining, such as surface subsidence, rock burst failures in the working face, and overlying strata fractures, have become increasingly prominent [1]. We constructed a mechanical model for the analysis of dynamic failures in a working face, in the presence of disturbances caused by underground mining, based on the effects of working face excavation on the stress states of the overlying strata. This model was used to provide the criterion for the dynamic failures in the overburden of the working face. The dynamics of stress transfers and failures in the overburden during mining process were obtained via a comprehensive analysis of the results obtained from our theoretical analyses, numerical calculations, and similitude experiments
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