Abstract
Fractures caused by mining are the main form of water inrush disaster. However, the temporal and spatial development characteristics of fractures of the rock mass due to mining are not clearly understood at present. In this paper, two geometric parameters, namely, fractal dimension and fracture entropy, are proposed to determine the spatial and temporal states of rock mass fractures caused by mining. The spatial and temporal structure characteristics of fractures in the rock mass due to mining are simulated with physical scale model testing based on digital image processing technology. A spatiotemporal model is created to examine the spatial and temporal patterns of hot and cold spots of the fractures based on a Geographic Information System (GIS). Results indicate that the fractal dimensions and entropy of the fractures network in the rock mass increase and decrease with the progression of mining, respectively, which can be examined in three stages. When the fractal dimension of the fractures in rock mass rapidly increases, the conductive fracture zone has a saddle shape. The fracture entropy of fracture has periodic characteristics in the advancing direction of the panel, which reflects the characteristics of periodic weighting. The fractal dimension and fracture entropy of fractures of the rock mass increase with time, and the rock mass system undergoes a process of increasing entropy. When the fractal dimension and fracture entropy of the fractures increase, the spatiotemporal state of fractures in rock mass caused by mining is initiated. When the fractal dimension and fracture entropy of the fractures decrease, the spatiotemporal state of fractures in rock mass is closed.
Highlights
There are many micro and macro primary fractures in a rock mass, such as joints, bedding and faults
In order to verify the universality of the criteria for determining the spatiotemporal state of rock mass fractures due to mining, the Mann–Kendall test was used to determine the trend in the spatiotemporal changes of the fractal dimension and fracture entropy of the rock mass fractures due to mining; z was determined to be 3.94
This indicates that the fractal dimension and fracture entropy of the rock mass strata increased with time, and the rock mass system underwent a process of increasing entropy
Summary
There are many micro and macro primary fractures in a rock mass, such as joints, bedding and faults. Coal seams have significant impacts on the rock mass especially when they are mined, because mining may cause fracturing of the rock mass, which can cause water and gas leakage [1,2]. Fractures will destroy the stability of the rock mass and even lead to water and sand inrushing, damage to groundwater resources, coal seam gas disasters, mining damage and surface environmental damage [3,4]. The study of fractal changes of the rock fracture network is of great significance to ensure safe mining under aquifers and to realize cleaner production in mines
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