Abstract
Ordovician limestone water on the floor is a serious threat to the safety of coal mine production in the Weibei coalfield, and prediction of the floor failure depth is the key for evaluating the mining conditions under pressure. This paper combines the hydrogeological conditions of the no. 5 coal seam and uses the FLAC3D program to determine the floor failure depth under two-factor (mining depth and width) and multifactor (mining depth, width, and height) conditions via numerical calculations and analysis. We obtain the fitting formula for the floor failure depth and analyze the influence of various factors on it. The results show that when the mining width does not exceed 200 m, the mining width has the greatest influence on the floor failure depth, followed by mining depth and mining height. In this paper, the working face floor failure depths measured values of 18 flat seams in China are taken as samples for comparison with the values calculated via empirical formulas and fitting formulas, and the maximum and minimum absolute errors and relative errors are analyzed. The nonlinear fitting regression formulas offered in this paper are found to provide strong predictive value, high accuracy, and a relatively small error range. The reliability and rationality of the models are further verified, thus providing a reference for future mining operations under safe aquifer water pressure conditions in the Weibei coalfield.
Highlights
With the gradual depletion of mining resources in shallow coal seams in China, the mining depth has gradually increased
According to the simulation results, it is found that the floor failure depth increases nonlinearly with increasing mining face width when the coal seam depth is fixed, but when the mining width increases to 140 m, the failure degree of the roof and floor increases greatly
To address the difficulty of predicting the no. 5 coal seam floor failure depth in the Chenghe mining area under safe aquifer water pressure conditions, this paper studies the floor failure depth trends based on a comprehensive column diagram and both physical and mechanical properties and draws the following conclusions: (1) The FLAC3D finite difference program and numerical simulation method are used to simulate the failure range of the floor plastic zone in the coal seam during mining
Summary
With the gradual depletion of mining resources in shallow coal seams in China, the mining depth has gradually increased. The first method is to depressurize the aquifer by releasing large amounts of confined water. This method causes pollution and waste of groundwater resources in the surrounding areas. The other method makes full use of the self-characteristics of the floor aquifuge to prevent the confined water from bursting into the working face or goaf [2]. When the support pressure from coal seam mining exceeds the ultimate strength of the floor rock mass, the floor will produce a failure zone with a certain depth [3, 4], which reduces the thickness of the effective aquifuge and increases the risk of water inrush. Determining the floor failure range is the key to preventing and controlling mine water disasters
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