Design principles and key technologies of gob side entry retaining by roof pre-fracturing

Abstract

This study investigates gob side entry retaining by means of roof pre-fracturing. Based on short cantilever beam theory, the entry roof was pre-fractured from gob roof via orientated blasting. The gob gangue was then blocked and used as one side wall of the retained entry. The blasting hole length relied on site geological conditions, and a design method was formulated. Yieldable cable bolt anchored into stable overlaying strata is one key technique to stabilise the entry roof under double dynamic pressure. For the gangue management I-steel and retractable U-steel formed frameworks were investigated with regards to varying seam thicknesses. A real-time remote monitoring system was developed and used to investigate surrounding rock mass deformation of the proposed retaining method and to provide early warning for mining safety. We present two working cases to show the applicability of the retaining method under different geological conditions. Field monitoring reveals that the periodic weighting loads decreased at the working face after roof blasting. The entry roof and gangue wall became stable after the working face passed a certain distance. Our proposed mining method provides an innovative approach for mining safety and economy.