Abstract
Because of the large deformation of surrounding rock mass and the different deformation characteristics of roadways with different cross-sectional areas, it is difficult to determine the means of support of roadways and the hole-sealing depth of extraction boreholes, which will cause serious roadway deformation and reduce the gas drainage rate. In order to solve these problems, this paper studies the evolution law of the zone of rock loosening around the roadway at four different cross-sectional areas (15 m2, 20 m2, 25 m2, 30 m2) by means of the acoustic field tests and numerical simulation. The results revealed three key points: first, the zone of rock loosening around the roadway is symmetrically distributed around the center of the roadway, and its shape is approximately that of a “butterfly.” Second, field tests results indicate that the rock loose zone of 1302 North floor mining roadway is in the range of 2.3–2.4 m on the side of the roadway and is 2.7–2.9 m on the central auxiliary transportation roadway. The simulation results show that the rock loose zone of 1302 North floor mining roadway is 2.5 m on the side of the roadway and is 3.0 m on the central auxiliary transportation roadway. The simulation results under four different section areas matched the field test results well, and the range of the surrounding rock loosening zone increases with the increased cross-sectional area. Third, the loose zone at the top corner and side of the roadway has a linear relationship with the cross-sectional area, and the loose zone at the bottom corner of the roadway does not change significantly with the cross-sectional area. These results have significance for determining the cross-sectional area of mine roadways in the same geological conditions, the sealing depth of the borehole, and the surrounding rock support.
Highlights
During the process of roadway excavation, the original stress equilibrium state of surrounding coal and rock mass is destroyed, and the surrounding rock mass changes from the original state of three-dimensional stress equilibrium to a two-dimensional stress state, resulting in an increase of tangential stress and a decrease of radial stress [1]
If the value of concentrated stress exceeds the strength of rock after falling, the surrounding rock will break, and this will gradually extend from the periphery to deeper layers, until reaching another new state of three-dimensional stress equilibrium [2]
We conducted the acoustic field tests to study the evolution law of the zone of rock loosening around the roadway under different cross-sectional areas
Summary
During the process of roadway excavation, the original stress equilibrium state of surrounding coal and rock mass is destroyed, and the surrounding rock mass changes from the original state of three-dimensional stress equilibrium to a two-dimensional stress state, resulting in an increase of tangential stress and a decrease of radial stress [1]. If the value of concentrated stress exceeds the strength of rock after falling, the surrounding rock will break, and this will gradually extend from the periphery to deeper layers, until reaching another new state of three-dimensional stress equilibrium [2]. During this process, a range of damage and looseness is initiated in the surrounding rock this is called the roadway-surrounding rock loosening zone. The determination of the reasonable sealing depth and distance of gas drainage boreholes is closely related to the size of the zone of rock loosening. It is important to Geofluids determine the distribution law of the zone of rock loosening for improving the efficiency of gas drainage, maintaining the stability of the surrounding rock, preventing accidental coal and gas outbursts and deformation of the surrounding rock, and ensuring the safe production of the coal mine [3]
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