Location selection and combined support of external staggered roadway with staggered mining

This study proposes a layout scheme for external staggered roadway and builds a mechanical model for unconventional coal pillars with staggered positions as a solution to the waste of resources caused by the large coal pillar size between the sections of 1301 fully mechanized top coal caving face and the difficulty in supporting the roadway in Xinjulong Coal Mine. We analyzed the stress environment and characteristics of the extreme equilibrium zone of unconventional coal pillars using the limit equilibrium theory. For the bottom roadway, the reasonable horizontal staggered distance in the lower section is set at 3.0 meters after considering its stress environment at different horizontal offset conditions and the distribution of elastic strain energy density of the section coal pillars. Meanwhile, we proposed a joint support scheme for adjacent roadways between sections. We simulated and verified the original support scheme and the joint support scheme in actual geological conditions during the mining stage of the continuous working face. Results show that the joint support scheme for adjacent roadways between sections outperforms the original support scheme. The peak stress of the joint support scheme reduced from 80 MPa to 64 MPa, with a reduction rate of 20 %, indicating that the it is more effective in controlling the surrounding rock of the roadway. Moreover, the unit reserved area of coal pillars in the section was 111.5 m2, which is a 34.4 % reduction from 170 m2 in the original support scheme. This study offers implications for reducing the reserved size of coal pillars in fewer sections and improving the coal recovery rate.