Research on failure criteria and collapse height of roadway roof strata based on energy accumulation and dissipation characteristics

Roof collapse is a form of rock failure driven by energy release. The rectangular elastic thin plate (RETP) model, widely used in coal mining engineering research, reflects the law of the movement of overlying strata of a coal seam. The stress distribution regularity of each delamination can be analyzed using the theoretical model of RETPs. In this study, a new method for determining both the height of the caving zone and the damaged area of the roadway roof is developed based on the energy evolution law. The damaged area and the oval-shaped boundary of each stratum are determined using the damage criterion deduced by calculating the strain energy of the elementary volume. As a case study, the collapse height was obtained by accumulating the thickness of damaged strata, and the length of bolts was increased from 2.2 m to 2.8 m, effectively preventing the reoccurrence of a roof collapse for the No. 30102 working face in Nanliang Coal Mine. In addition, the vertical boundary of the caved zone can be outlined by connecting and fitting the end vertexes of the minor axis in the oval-shaped damaged area of the RETPs. The supporting angle of the bolts in two side walls of the roadway was decreased from 75 degrees to 70 degrees. This method was verified and applied in a roof collapse investigation by determining the length and drilling angle of the anchor rod and anchor cable required to develop reasonable support schemes. The results of this research can be used for ensuring safety in coal mining and subway or tunnel construction in China.