| Exploiting protective layer is a preferred and effective regional prevention measure for controlling coal and gas outburst. Its key issues were the location of the effective protection region of protected layer and the effective extraction of pressure-relief methane gas. Due to the particularity of pressure-relief law in exploiting steep-incline upper-protective layer with a bow pseudo-incline technique (SULBPT), the application of the traditional locating method of protection region by referring to the reference values of in exploiting SULBPT could not be carried out. Withal, in this paper, regarded the SULBPT at Donglin coal mine as the project background for this study, the discrimination criterion and locating method for the protection region of SULBPT was investigated by incorporating the experimental study, the theory analysis and the numerical calculation; According to the practical investigation results of the protection region of SULBPT, the rationality and reliability of the theory analysis was checked. Based on it, an optimization designing and an effect monitoring on extracting pressure-relief gas of SULBPT was carried out by utilizing the effect"pressure-relief to strengthen permeability". These conclusion and results can be drawn that:①The basic physical-mechanics parameters of surround coal/rock and the dynamic changing laws of permeability in the coal with low permeability at investigation area are confirmed by the compression test, the tensile test, the shear test and the experiment of methane gas flow in coal with coal-gas burst hazard and low permeability under action of triaxial stresses, respectively. The test results show that the equivalent pore pressure coefficient increases approximate linearly with the increasing pore gas pressure and decreases approximate linearly with the increasing bulk stress; the Klinkenberg effect of methane gas flow in low permeability coal is especially prominent, and the Klinkenberg coefficient and the absolute permeability are relating to a power function meanwhile the absolute permeability and bulk stress is relating to a quadratic polynomial function.②Based on the unstable theory of coal and gas outburst, the dynamic unstable model coupled solid deformation and gas flow in coal and gas outburst under finite deformation is founded. Based on it, the ultimate methane gas pressure of coal seam at the investigation area is gotten. ③A discrimination criterion found on ultimate methane gas pressure for protection region of exploiting protective layer was put forward, that was the protected layer area, whose remaining pressure was less than its ultimate methane gas pressure, were discriminated as the effective protection region for exploiting protective layer. The results show that this discrimination criterion reflects the effect of stress, methane gas pressure and the structure of coal on the coal and gas outburst.④Based on the theory of pressure-relief gas flow leak in exploiting protective layer, the dynamic model of pressure-relief gas flow leak in exploiting upper-protective layer coupled solid deformation and gas flow is founded; The distribution laws of gas pressure of protected layer after exploiting upper-protective layer are obtained by solving this model. The research results show that this model reflects the effect of the changing law of effective stress, the dynamic changing of porous rate and permeability of coal with low permeability, the delaying process of gas desorption and the common action mechanism of coalbed methane gas flow and diffuse on the pressure-relief gas flow leak.⑤The locating method of protection region in exploiting protective layer based on the discrimination criterion of ultimate methane gas pressure is developed. This method can preferably reflect the condition of gas flow leak and coal deformation of protected layer in exploiting protective layer; Aimed at the Donglin coal mine, the effective protection region of SULBPT is located by the discrimination criterion of ultimate methane gas pressure and coalbed deformation. The theoretical calculation results show that the strike pressure-relief angles of the upper, middle and downside of the working face of protective layer located by the discrimination criterion of ultimate methane gas pressure have little difference, the strike pressure-relief angles of protection region of SULBPT decrease from superficial to deep and are among 43.2 degree to 40.7 degree; The pressure-relief angles located by the discrimination criterion found on ultimate methane gas pressure and coalbed deformation are closer and the back'results are larger than the former.⑥The protection region for exploiting protective layer at investigation area were tested by the practical investigation experiment of SULBPT. The investigation results show that either the pore gas flux or the gas pressure of protected layer go through the pressure-relief process for two times along with the exploitation of working face of protective layer and that the strike pressure relief angle along the oblique working face of the protective layer is 43.5 to 53.6 degrees and the underside of SULBPT has a pressure relief angle of 78.7 degree. The practical test values and theoretical values of the protection region of SULBPT are closer and the theoretical values are safer, which show that it was reasonable and reliable for the theoretical calculation method put forward by this paper.⑦An optimization designing method on extracting pressure-relief gas of protected layer, that the arrange parameters of extracting were determined by analyzing the moving characteristic of downside pressure-relief rock mass and the law of pressure-relief gas flow in SULBPT, utilizing the effect"pressure-relief to strengthen permeability"in exploting protective layer and integrating the practical condition of investigation area, was put forward. The monitoring results on pressure-relief gas extracting show that the average extracting rate of pressure-relief gas is reach to 50% by using the optimized extracting arrange parameters designed by this paper.
|
PDF Full Text Request