Distribution pattern of overburden void ratio induced by mining in goaf areas and corresponding zoning-based control measures

In response to the pressing need for surface land resource utilization and engineering safety associated with large-scale coal mining in China, the study is based on the formation and spatial distribution of goafs in a mine located in Jiaozuo. A combined approach of numerical simulation, theoretical analysis, borehole detection, and physical exploration was adopted to analyze the development and spatial distribution characteristics of overburden fractures induced by mining in the goaf areas. The fractal analysis method was introduced to construct a void ratio analysis model for the mining-affected region, examining the spatial distribution and evolution of overburden void ratios. Based on the current conditions of the goaf areas in the study region, a multi-segment treatment scheme and engineering control methods for different segments were proposed. The study indicates that, as the working face progresses, the fractures exhibit an overall “upward-forward-stable” evolution pattern, accompanied by periodic changes of opening, closing, and compaction. In the early stages of mining, the fractal dimension of the overburden exhibits a rapid increase (with an increment of 10.9%). The complexity of the fracture network shows a significant positive correlation with the fractal dimension, and the interlayer significantly affects the fractal dimension. The fractal dimension on the side of the goaf opening decreases from 1.7 to 1.3, while the side of the working face remains around 1.3. During the full mining stage, the distribution presents a “八” shape, revealing the synergistic evolutionary mechanism of high-position fracture closure and low-position compaction. A void ratio extraction model based on fractal image features is proposed, along with a quantitative expression formula for the void ratio. This model realizes the coupling expression of fracture geometric complexity and void characteristics. Based on the regional differences in void ratio distribution, the area is divided into structural fracture zones and compaction fracture zones, with void ratios of 0.75, 0.62, and 0.25, respectively. This provides a basis for graded management in different regions. The simulation results are in high agreement with field borehole and geophysical data, verifying the reliability of the model. Based on the residual cavities and fracture zoning characteristics of the collapse zone, a multi-stage grouting treatment method based on the fractal-porosity synergistic identification approach is proposed, achieving precise grouting in multiple stages and the penetration and diffusion of the grout in different fracture types. The research findings have significant guiding implications for the management of similar mined-out areas as construction sites.