Physical simulation of upper protective coal layer mining with different coal seam inclinations

Abstract

Protective coal layer (PCL) mining is a preferred regional method for preventing coal and gas outbursts; stress‐relief of PCL mining is the prerequisite of pressure‐relief gas drainage. In order to study the stress‐relief effect of PCL mining on protected coal seams and determine the protection scope of PCL mining under different inclinations, this paper uses physical simulations to study the stress‐relief law and deformation characteristics of the strata during upper PCL mining with a gentle inclination (25°), an intermediate inclination (45°), and a steep inclination (65°). The results show that as the coal seam dip increases, the degree of deformation and failure of the overburden strata gradually decreases, the severe subsidence and expansion area of the overburden strata tends to gradually develop in the uphill direction of the working face, and the floor strata underlying the protective seam significantly expand toward the goaf. However, the absolute value of the upward movement of the floor strata is much smaller than that of the roof strata; and the greater the dip angle, the greater the ratio of floor displacement to roof subsidence. The stress‐relief curve of the protected layer is approximately U‐shaped. As the inclination of the coal seam increases, the stress‐relief range decreases gradually. The maximum relief‐stress and the stress release coefficient of the protected layer initially increase and then decrease. The stress concentration coefficient of the protected coal seam initially increases first and then decreases in both uphill and downhill of the working face in the PCL. As the inclination increases, the stress‐relief angle of the downhill boundary initially increases and then decreases, while the stress‐relief angle of the uphill boundary decreases gradually. Our research results provide guidance for the delimitation of the protected scope of PCLs with different dip angles.

Variation law of roof stress and permeability enhancement effect of repeated hydraulic fracturing in low‐permeability coal seam

“…According to similarity theory, when studying the stress and strain of materials, the test model and material should be geometrically similar to the research object, and the bulk density and stress should be similar. [28][29][30][31] 1. Geometric similarity When conducting simulation experiments, the geometric dimensions of the experimental model and the prototype should be similar:…”

Mechanisms and Applications of Pressure Relief by Roof Cutting of a Deep-Buried Roadway near Goafs

“…To delve into the mechanism of pressure relief by roof cutting for an RNG, firstly, the overlying rock structure and migration law of the adjacent roadway should be studied to find the source of the high stress in the surrounding rock of the roadway; meanwhile, a physical simulation experiment is an effective method to study the structure and migration law of overburdened rock [23][24][25]. Therefore, in this paper, based on the mechanical roadway of the 121,302 working face in the Kouzidong coal mine, through physical similarity simulation, the overburdened structure and migration law of the RNG are studied.…”

Stress Distribution and Gas Concentration Evolution during Protective Coal Seam Mining

“…e deformation would tend to decrease as the distance increases and hence the crack initiation and propagation would be limited. Fang et al [17] investigated the effect of the dip angle on the stress relief and deformation of the coal seam during the extraction of the protective coal seam and they concluded that as the dip angle increases, the deformation and damage in the overlying coal seam tend to decrease. Qin et al [18] believed the computational fluid dynamics (CFD) is the optimized method for coal seam gas drainage design.…”