Optimization of Stope Sidewall Controlled Blasting Parameters for High-Stress Fan-Shaped Medium-Depth Hole
At present,most of the fan-shaped hole stope blasting is difficult to achieve direct control of the sidewalls,and fan-shaped holes due to the special characteristics of its own structure can not be avoided to cause a certain amount of over-excavation or under-excavation.Aiming at the problem of controlling the sidewalls of the blasting of fan-shaped holes in the stope,a concept of constructing the fan-shaped holes close to the sidewalls into vertical parallel holes for controlling the sidewalls was proposed.Sidewall controlled blasting technology generally utilizes air-uncoupled charge structures to achieve.The model parameters of four groups of parallel boreholes under the uncoupling coefficient and spacing matching were obtained by theoretical calculation.The numerical simulation was carried out by LS-DYNA,and the blasting crack propagation of the four groups of models without in-situ stress and in different directions of in-situ stress was compared.The stress conditions of the three schemes are different.In scheme 1,four models are numerically simulated under the condition of no ground stress.In scheme 2,when the direction of the maximum horizontal stress is the same as that of the stope layout,30 MPa is loaded in the X direction and 60 MPa in the Y direction.In scheme 3,when the direction of maximum horizontal stress is perpendicular to the direction of stope layout,60 MPa is loaded in X direction and 30 MPa is loaded in Y direction.After analyzing the blasting crack propagation and blasting effect,it is found that high geostress promotes the propagation of blasting cracks in the direction of the maximum stress.When the stope is arranged parallel to the direction of maximum horizontal stress,the propagation of blasting cracks in the rock between the lines of the blast holes is promoted,which is beneficial to the breaking of rock.The propagation of blasting cracks in the rock between the blast hole and the surrounding rock will be restricted,which is beneficial to the protection of the sidewalls.When the stope is arranged vertically along the direction of the maximum horizontal stress,the propagation of blasting cracks in the rock is promoted,which is not beneficial to the protection of the sidewalls.Therefore,the direction of the stope layout should be the same as the direction of the maximum horizontal principal stresses.Statistics on the four models of excavation area damage rock,the uncoupling coefficient of 1.65,neighboring parallel hole spacing of 1.1 m is the most reasonable.Industrial experiments were carried out in the test stope,using the optimized blasting parameters for blasting,and the sidewalls were smooth and stable after the stope was mined,which verified the reasonableness of the blasting scheme.
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