Stability analysis of stope retention pillars in broken rock conditions

After a proper engineering geological evaluation with rock mechanics rating(RMR) method,Q system and geological strength index(GSI),the mechanical parameters of rock masses were obtained by the extended Hoek-Brown failure criterion.According to the pillar layout of Baiyang ore section,a formula of pillar load was derived,and some parameters for calculating the pillar strength were also determined.The pillar instability mechanisms were respectively analyzed in view of main failure modes.Orthogonal design was introduced to optimization of the stope structure parameter.On this basis,the three-dimensional numerical simulation of each mining program was carried out.The sensitivity of influencing factors for pillar stability was assessed using the method of orthogonal range analysis.The practice shows that the stability of retention pillars can be safeguarded when the stope height is controlled in the range of 3.5 to 4.5 m,the stope width less than 5 m,and the pillar diameter not less than 3.5 m.