Studies Of Stability And Control For The Mined-out Stopes Group At A Gypsum Mine In Hebei Province

Experimental analytical, theory analysis and numerical methods were used to study the stability and control for the mined-out stops at a gypsum mine in Hebei province.The main research work and achieved results are as follows.(1) RMT-150 B rock mechanics testing system and DHZ-1 point load tester were used to measure the mechnical properties of gypsum ore body, roof and floor; and, when the mudy gypsum ore sample was soaked with water, its compresive strength would drop to 20-30% of the dry sample.(2) FLAC3 D was used to model the stability of the mined-out stops at the mine. The results indicated that most of the mined-out stops were stable, that failure happened in a few mined-out stops and that a few pillars have very strong vertiacl stresses.(3) The height of the transmisive fracture belt in the roof of the mined-out stope under the river was analysed and calculated.The thickness of the impermeable layer was about27.2m and the surface water will not be transmissed into the mined-out stopes.(4) Safety factor method was used to analyze the stability of the pillars. The measures for controling the stability of the mined-out stops were proposed by using the analytical results for pillar stability, numerical results and the calculation results for the height of the transmisive fracture belt. Three brick pillars, each with a cross sectional area of 2×2 m2, have to be constructed on the central line along the strike of mined-out stops C2, B6 and B8. The spacing between the brick pillars is 8m.(5) In the subsequent mining operation, room and pillar mining method has to be used,the span of the room has to be between 8-10 m, and the span of the continous pillar on the two sides of the transport tunnel has to be larger than 4m.