Experimental and numerical investigation of energy dissipation of roadways with thick soft roofs in underground coal mines

The roadway deformation process is closely associated with the accumulation and dissipation of energy. Understanding the characteristics of energy dissipation in surrounding rock is critical to revealing the development process and the disaster mechanisms of the roof accidents in underground coal mines. This paper presents a triaxial compression experiment to analyze energy characteristics of mudstone taken from Huangyanhui Coal Mine. A numerical study is performed to study the energy distribution under different roof strengths. The results suggest that the instability of the roadway is an irreversible energy dissipation process with high nonlinearity and complexity. The roadway support principle, based on the energy balance theory, is proposed to explain the energy distribution. The safety control of roadways with thick and soft roofs should consider the following three aspects: (a) optimize the layout of the roadway, avoid placing it in the stress concentration zone, and reduce the strain energy of the surrounding rock accumulation from the source; (b) improve the ability of the supporting structure to adapt to the deformation of the surrounding rock and avoid the failure of the supporting structure because of excessive force; and (c) set weak structures in the surrounding rock, that dissipate part of the energy, thus reducing the load acting on the support. The results of field application monitoring show that roadway severe deformation was effectively controlled using pressure relief boreholes (PRB), and the average floor heave speed of the roadway decreased from the original 2.0 to 0.98 mm/d. Therefore, PRB provides a new approach for roadway control.