Filling Pillar Width And Roof Subsidence In Tiaoshuihe Phosphorite Mine

Stability of filling strip pillar had great influence in safety in mining,plastic zone width and gob width of filling strip pillar was closely related to its stability.Because Tiaoshuihe phosphate mine was located in a mountain area,the cost of filling materials was high,part tailing strips displacement filling mining method was chosen,the ratio between filling areas and mining areas was required to be less than 0.5.In order to choose suitable filling material,filling width and gob width,this paper would research plastic zone width,core zone width,gob width and roof subsidence through theoretical calculations and numerical analysis.Those were the major results:（1）Considering intermediate principal stress and pillar weight,sided pillar plastic zone width formula under limited state was derived by DP yield criteria and striped pillar ultimate strength.According to theoretical calculations and numerical analysis,DP3 criteria was more conservation than MC criteria,which means it was safer in practice（2）Because stress changes on the top of pillar core zone was approximate to quadratic curve hypothesis and the plastic zone stress curve was a straight line,the relation between core central stress and the pillar ultimate strength was gotten.then the formula between pillar width and gob width on both sides was derived based on stress balance principle.（3）The order of roof sinking was:Ph₂ phosphate pillar compression→bearing strata first compression→filling strip pillar compression→bearing strata second compression,with the development of strip mining,overburden subsidence ultimately form a wave-shaped curve.So the key strata theory was used to judge key strata,then the roof subsidence was calculated through bearing rock compression and striped pillar compression theory.（4）Compared to numerical analysis,according to the theoretical formula between plastic zone width,core zone width and gob width,the best lime-sand ratio is1:5,filling pillar width is 14m,gob width is 14m,then the roof subsidence is 92.3mm,which could ensure mining safety and save filling material.