Analysis Of The Influence Of Tectonic Comress Stress Over Coal-mining-induced Subsidence

The pattern of tectonic stress of China is controlled by the dynamic process of surrounding lithosphere plates. The regional tectonic stress field of China can be roughly divided into two areas, East China Stress Area (A) and West China Stress Area (B). Coal mining areas in China mainly distribute in Northeast Stress Subarea (A11), North China Stress Subarea (A12), South China Stress Subarea (A20) and Xinjiang Stress Subare(aB10). In some coal mining areas horizontal tectonic stress is bigger than vertical gravity, therefore the forecast value of coal-mining-induced subsidence would markedly warp actual situation if tectonic stress were ignored.The control function of tectonic compress stress on coal-mining-induced subsidence is studied in this thesis by means of theoretical analysis, numerical test and similar material simulation, based on the geological and caving conditions in typical coal mining areas.The result of numerical test indicates that when the tectonic compress stress is less than the critical failure stress of overlaying rock layres, it can mitigate coal-mining-induced subsidence. Under the action of compress stress the deformations of the floor of coal seam and working increase with workface advancing continually, whereas only under the action of the gravity of overburden although the floor of coal seam and working deform also with workface advancing, the deformation extent is smaller than that under the action of compress stress .The result of similar material simulation test proved that the ground environment damage induced by coal caving appears later and lower-grade under the condition of compress stress than that there is not tectonic stress. So tectonic compress stress has the function of restraining coal-mining-induced subsidence. Under the two stress conditions mentioned above, the ultimate shapes of subsidence basin on surface and profile and filling ratio of a gob are all different. A longer hanging rock beam and a bowl-shapeed basin may form under the the condition of tectonic compress stress, whenas the hanging rock beam would be shorter and the subsidence curve would be"V"shape if there were no tectonic stress.Studying the influence of the relationship between the strike of long axes of a gob and the direction of the maximum principal tectonic stress over coal-mining subsidence, it is discovered that in coal mining areas there existing higher tectonic stress the stress concentration degree and deformation extent within wall rock nearby a gob increase evidently with the angle between the strike of the long axes of a gob and the direction of the maximum principal tectonic stress changes from 0°to 90°. Therefore, sufficient attention should be paid to the azimuth of horizontal tectonic stress so as to make the strike of long axes of a gob parallel with the maximum principal tectonic stress when a workface is designed.