Abstract
Fracturing roofs to maintain entry (FRME) is a novel longwall mining method, which has been widely used in China, leading a new mining revolution. In order to research the change law of side abutment pressure and movement law of overlying strata when using the FRME, a new abutment pressure monitoring device, namely, the flexible detection unit (FDU), is developed and is applied in the field. The monitoring results show that compared with the head entry (also called the non-splitting entry), the peak value of the lateral abutment pressure in the tail entry (also termed the splitting entry) is reduced by 17.2% on average, and the fluctuation degree becomes smaller. Then, finite difference software FLAC3D is used to simulate the stress change of the solid coal on both sides of the panel. The simulation results show that the side abutment pressure of the tail entry decreases obviously, which is consistent with the measured results. Comprehensive analysis points out that after splitting and cutting the roof, the fissures can change the motion state of the overlying strata, causing the weight of the overburden borne by the solid coal to reduce; therefore, the side abutment pressure is mitigated.
Highlights
The technology of gob-side entry retaining (GER) has been widely utilized worldwide since it was put forward in 1950s [1,2]
The results further indicated that the constant resistance large deformation (CRLD) bolts had the characteristics of high support resistance, large elongation, absorbing energy, and negative Poisson’s ratio effect
In order to discuss and investigate the evolution laws of the side abutment stress in the tail entry and head entry and the influence of the fracture and movement of overlying strata on gateway stability after using the Fracturing roofs to maintain entry (FRME), 12 sets of the flexible detection unit (FDU) were installed in the solid coal of the head entry and tail entry of 100 m in front of the coalface to monitor the changes of coal mass stress, independently
Summary
The technology of gob-side entry retaining (GER) has been widely utilized worldwide since it was put forward in 1950s [1,2]. Many experts and scholars have conducted research on FRME, obtaining a series of rich results He et al [9] invented an energy-absorbing bolt with large elongation and high constant resistance. Fan et al [15] set up a mechanical model of the FRME and studied the vertical stress and displacement of the coal wall under different heights and angles of the roof cutting through UDEC software. He believed that the FRME could reduce the vertical stress and stress fluctuation of gateway roof He et al [6] investigated the loads monitoring of hydraulic support at different positions on the panel of thick coal seams. Its main technical specifications are as follows: the measurement range is up to 60 MPa, the length 500 mm, the Energies 2021, 14, 475
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