Study Of The New Method Disposing Gently Inclined Abandoned Stope And Ground Pressure Control At The Stope

In the present thesis, according to the practical condition of Dongtongyu Gold Mine, a new method that dilapidating the mine roof by cutting grooves through controlled explosion in disposing the mining abandoned-stope is put forth, and a new theory of designing the pillar in hard-rock mine, which can be used to control the stope pressure is brought forward. The main work and conclusions are as follows.(1) The formulas of roof cutting location have been deduced from strength theory of materials, in which the roof is assumed as rock-beam. The mechanical characteristics of the roof at abandoned stope have been analyzed. The results show that cutting roof nearby 966m level is reasonable when only the ore above 866m level is mined, which can make the pressure distribute again in roof toward that is benefit to safety production. Second roof cutting should be performed nearby 796.7m level if ore is mined continuously to 780m level. The calculating formulas can only be used for continuous and regular abandoned stope, otherwise large deviation of cutting position occurs,for instance, the deviation of analytic result for the second cutting position(796.7m) is larger.(2) Two dimensional software of finite element analysis (NFAS) improved from NCAP-2D has been applied to analyze the stress-characteristics of the roof in Dongtongyu Gold Mine. The calculation element amount i. e. 500 of NCAP-2D is raised to 3000~5000. NFAS can generate grid automatically, deal with several boundary loads, and export freely the graphs of the grid information and calculation results by typewriter. The results show that cutting roof nearby 866m and 966m level is reasonable if ore above 750m level is mined entirely, and the roof stress will distribute again toward that is benefit to safety production and obvious surface subsidence and rock movement can be prevented.(3)On the basis of the conclusions from literatures and theoretical analysis, a new method that dilapidating the mine roof by cutting grooves through controlled explosion has been put forward. The most tensile roof of the abandoned-stope is grooved with certain width along all strike through controlled explosion so that the caving will happen earlier here and cause caved rock and caved roof to touch upper roof as far as possible. As a result, the abandoned stope is transfigured and separated from lower mining system, the hidden dangerof large scale roof sudden falling is eliminated, and the roof stress distribute again toward that is benefit to safety production. This method can also weaken the shock wave in air resulted by roof uncontrolled caving. To fully use the abandoned-stope, decrease the speed of refuse rock throwing onto hillside and prevent the deluge of the refuse and soil, mining wastes is programmatically threw into steeply inclined abandoned stope and simply hurled in the disposed and the gently inclined abandoned stope.(4)The formulas of roof cutting depth has been deduced from the damage and fracture theory, and the formulas of roof cutting width has been deduced from air dynamics of underground mining. Combining these formulas with the roof cutting location, the theoretical system of formulas for dilapidating mine roof by cutting grooves through controlled explosion has been composed.(5)The formulas for the pillar space have been deduced from strength theory of materials. Combining the classical theory of rock mechanics and the newly appearing pillar strength theory of hard-rock mine with the pillar space, new theory of designing te pillar in hard-rock mine has been brought forward. The theory has been applied in Dongtongyu Gold Mine in order to control stope pressure.(6)The tests and some experiments of the present thesis have been applied and fulfilled in Dongtongyu Gold Mine, which has brought enormous direct economic efficiency (more than 34 million Chinese Yuan) and great social significance. It is suitable to be applied in gently inclined and horizontal hard-rock mine.(7) In the present thesis, the effect of roof cutting is monitored and evaluated by acoustic emission over a long period of time. It is economic, convenient and efficient. The use of this method extends the scope of applying AE.