The Numerical Simulation On Optimization Of Stope Room And Pillar Sizes In Level 435 Of Dahongshan Copper Mine, China

The mining methods of Dahongshan copper mine on level 435 at present are sublevel open stoping with subsequent filling. The principles of stope design point out that the maximum span of roof generally do not exceed 36m, the thickness of level pillar(top and bottom) 10m, the thickness of pillar between stopes 5m and the thickness of interlayer 14m. While in the actual production process, the span of some stopes is more than 36m and roof falling happen frequently. Therefore for the sake of ensuring the stability, it is needed for us to adjust the dimension of stope and study the distribution of stress in rock mass around the stope. Meanwhile, on level 435, the distance between I2 and I3 ore body with a high grade is short. If we leave the interlayer of 14m according to the design requirements which are high grade of Ib and I2 ore body, it will obviously cause resources and economic losses so that we should consider to recycle that part as far as possible. In order to decrease the ore losses, it is better to reduce the thickness of interlayer as far as possible. Through numerical simulation, it is found that remaining point pillar in the middle of the stope in different sizes would reduce the span and increase the stability of the stope. Meanwhile the influence of interlayer thickness changing on stress distribution has also investigated.Numerical simulations with finite element method are adopted to finish the work of this paper. Analyzing has been performed with a 2-D finite element model, on the values and ratios between the horizontal component Q and the vertical component P (coefficientλ) of initial stress in rock mass obtained by different authors in Dahongshan copper mine and Dahongshan iron mine. Most possibly values of initial stress in rock mass and the coefficientλhave been obtained by comparison the result of 2-D finite element model and the stability condition of rock mass.A large number of numerical simulation models have also been established to simulate the stope room with different spans and different sizes and thickness of interlayer, as well as different pillar heights and thicknesses. Analyzing is then conducted on stress distribution and stope stability. Main conclusions are obtained as follows:(1) The report from measurement results of one units point out that the valueλ, the ratio between horizontal component and vertical one of the initial stress in rock mass, are among 0.56-15.68. While the report from measurement result of another unit shows that the value ofλare 0.71-0.92 along the direction of major principal stress and 1.19～1.37 along the direction of least principal stress. Analyzing result by comparison stress values in the rock mass and the rock strength show that the real value ofλin rock mass, would not more than 1.5 and value ofλx=0.82 andλz=1.3 are reasonable. (2)With the reducing of the interlayer thickness, the value of the tensile stress in the rock mass of interlayer increases and the distribution range of the tensile stress also expands. When the thickness of interlayer increases to over 14m, the safety coefficient also increases, though not significantly. Therefore it is reasonable to keep the thickness 14m. (3)The main factors influencing the stability of interlayer rock mass are the strength of rock itself and the stope span. Under the present condition, the span is unfavorable to exceed 36m. (4) A wide range of tensile stress exists in the roof rock of the middle part of the stope, and whether there is a point pillar, it has great influence on the distribution of tensile stress in the roof as well as roof stability. When there is a point pillar, the stability of the roof will be greatly improved. Therefore, in case that the span is more than 40m and the room area is more than 2000m2, it is necessary to add point pillar in the stope. (5) Under the possible condition that the thickness of ore is comparatively small or the ore in the interlayer is rich, it is also feasible to add point pillar for decreasing the thickness of the pillar so as to increase resource recovery even though the room span is not much large. (6) The stability of the pillar is not only concerned with the thickness, but also concerned with the height. Hence, under the condition that the ore thickness as well as pillar height are relatively small, it is better to reduce the thickness of the pillar appropriately so as to improve resource recovery. For example, when the height of pillar is less than 15m, it may make the pillar thickness 5m. (7) In some stopes, the shape is trapezoidal and the length of the stope on one side is more than 50m, which make a large span on local position, large mount of supplying ore and time extension. In order to deal with this situation, it is considered to establish some temporary pillar where there is a comparative large span in the process of excavation. The temporary pillar will not be exploded until other part of the stope being exploded and finishing the supply ore. And then conduct the process of high strength for supplying ore, sealing and filling. Hence, the time of large roof exposing will be much shorter, which is good for the roof stability. In order to ensure that the temporary pillar rock will not occur obviously deformation damage and explode successfully in later steps, the pillar size should be large enough and the sectional area should be more than 200m2. Meanwhile the ratio of height and thickness is unfavorable to exceed 2-2.5.