Research On Disturbance Characteristic Of Floor Strata In Goaf Above The Confined Aquifer

With the exhaustion of coal resource in the superficial part, the coal mining develops to the deep. Simultaneously, as the pressure of the groundwater increases,the number of coal mine suffered from the confined groundwater grows. It is well known that the high pressure groundwater environment in the underground work place not only rising the cost of the mine drainage, but also inducing the water burst accident. Therefore, it is significant to control the groundwater influence in the underground work place efficiently so as to ensure the human safety and achieve the mine safety production. The safety prediction of coal seam mining under pressure is an important precondition to control the groundwater effectively, it is feasible to judge the possibility of roof strata failure by the disturbed value of the floor strata, then analysis the safety of the coal mining; The disturbance regularity of floor strata could be gained by reliable computational methods, and simulated to obtain the disturbance regularity of floor strata in the goaf of different conditions, it provides the basis of measures development to improve the geological environment of floor strata effectively and the unnecessary investment waste could be avoided.Scholars of domestic and abroad has been carried on the study of the prediction of coal seam mining under pressure for years, they proposed several computational methods to analysis the safety of mining under pressure, these methods are meaningful to the prediction of the water burst possibility of the floor strata in the goaf, however, these studies dispose the pressure of the floor strata in the goaf as uniform or linear distribution, they did not consider the development process of the roof strata “Vertical three zones” and the influence of roadway rib supporting to the distribution of floor in the goaf. In the condition of external force in different hypothesis, the disturbance regularity of floor strata would change; it leads to the inaccuracy of the prediction of the coal seam mining safety. Therefore, the disturbance regularity of floor strata in goaf needs to be carried out under no uniform loading patternsThis thesis applies the theoretical analysis, field trial, numerical simulation and other methods to study the disturb law of floor strata systematically, obtains researchresults as follow:(1) In the influence of mining, there are two kinds of condition that the floor water proof strata affected by the roof strata: when the thickness of floor water proof strata and pressure of artesian water are bigger, the pressure of the floor strata by caving zone and fractured zone have small impact on the incremental deformation of the floor in the goaf. The maximum of the deformation value of floor water proof strata in the goaf is increased as the working face advance. Until the weight of the bending subsidence zone starts to influence on the surface of floor in the goaf, the maximum value of the floor water proof strata begins to decrease. When the thickness of floor water proof strata and pressure of artesian water are smaller, the pressure of the floor strata by caving zone and fractured zone have great impact on the incremental deformation of the floor in the goaf. After the first weighting, the maximum of the deformation value of floor water proof strata in the goaf begin to decrease. Therefore, it is necessary to consider the character of roof caving in the mining process, and analysis the thickness of floor water proof strata and pressure of artesian water synthetically.(2)Applying the FLAC3 D numerical simulation software based on the continuous medium, the thesis constructs the mathematical and physical models, by comparing of the results between the field test and numerical simulation, tests the correctness the model; according to the result of the numerical simulation of the floor strata, the law of floor distribution in the goaf with the mining influence was obtained.(3)Using the communicating principle, the thesis develops the “Point elevation dynamic measure device in hidden project”, it could measure the disturbed value of floor strata when there is no reference level; combined with the condition of field, the thesis analyses the affect of negative factors to the measure results, the measure error mainly roots in the variation of temperature between the testing roadway and goaf; the thesis exerts the device to measure the disturbed value of floor strata in vertical direction in the goaf, gets the disturbed curve of the floor strata in the goaf as the mining of working face.(4) The law of disturbed value of floor strata in the rear of goaf is that it increases firstly and then decreases. At the beginning of mining face, the disturbedvalue upward of the floor strata in the goaf increases, and the maximum value locates at the central area in the rear of goaf; the disturbed value decreases gradually and distribute as a fan, the disturbed value are smaller in the area of working face and roadway. When the mining distance of working face is longer, although the unloading area of floor in the goaf gradually increases as the mining continue, the floor strata of the rear goaf are suppressed by the fallen rock mass and the disturbed value decreases;however, with the supporting of the working face and roadway, the surface pressure of the floor strata of the front goaf are lower; meanwhile, the maximum of disturbed value locates in the area relative to the middle of the front goaf, the isoline of the disturbed value is elliptical, the value decreases at the edge of the goaf. When the disturbed value of floor water proof strata in the front of the goaf achieves the maximum, the value would not change significantly.