Study On The Dynamic Course Of The Surface Subsidence And The Model Based On Theory Of Key Rock Stratum

The first Importance technological problem of coal mining under railway ,surface structure and water body is predicting and controlling the surface subsidence due to underground mining. The way of predicting the surface subsidence based on the theory of the probability integral is only obtained the static subsidence index such as the amount of subsidence ,incline and curvature at present. But this model is not described the whole surface subsidence course. The degree of the damage to building and structure not only is determined to the final surface subsidence due to underground mining but only the surface subsidence velocity and acceleration especially to the structure sensitive to the deformation just like railway , telecommunication line and mountain coast. So, the research of the dynamic course of the surface subsidence due to underground mining is profound theoretical and practical significance. The object of study in this paper is the rock stratum movement and surface subsidence up the long-wall mining coal face. Through the way of the field observation, numerical analysis mining, theoretical analysis, mathematical modeling and test by observation data, studied the dynamic course of the surface subsidence due to underground mining,obtain the following conclusion.1) A function model of the subsidence, incline and curvature is set up suited to the condition of mining coal by long-wall face. The parameter a and b determine the subsidence basin range and the parameter wmax and d determine the depth of the subsidence and the shape of the subsidence curve of the section of the basin in this model. This model can fit well the observation data. It is more advanced than the negative index function and hyperbolic tangent because of the function is brief and the parameter is obtained easily.2) The viewpoint in this paper is the suface subsidence is detemined by bend of the rock stratum near by the surface when the ratio of depth of embedment and thickness of the coal seam is very large up long-wall mining coal face. This key rock stratum is controlled the surface subsidence. The size of the surface subsidence is far below the rock thick. So the bend is fit for the theory of the flexible sheet.3) A surface subsidence basin model due to underground mining is seted up used the theory of the key stratum and elasticity sheet and inferd the formular of the parameter d and the excursion of the maximum dot on the y axis of the steep coal seam in this paper. 4) By analyzing the dynamic course of the surface subsidence due to underground mining coal, the conclusion has been drawn that the w-t curve of the ground subsidence appears S-shaped. So the time function which can describe the subsidence course of the ground must fit not only the w-t curve but also the v-t curve and the a-t curve. Time functions which are usually used to fit the w-t curve of the foundation or roadbed settlement now such as the exponential time function, the hyperbolic time function, the Gompertz time function, the Logistic time function and the Weibull time function. Studying the w-t curve, v-t curve and a-t curve of these time functions finds that these times function is not feasible for describing the dynamic course of the ground subsidence due to underground mining.5) By adding a constant parameter k to the Knothe time function, a new time function model has been set up. The velocity and acceleration worked out from this new time function model is in accordance with the dynamic process of the surface subsidence. In this new model the parameter c decides how long the subsidence would continue; and the parameter k decides the path of the subsidence on the axis of time.6) The time parameter t is replance by the space parameter l of the mining face moving and the speed parameter v0 when the coal minging face is moving with a constant speed and the begin parameter l0 the surface subsidence.7) Use the FLAC^3D to simulate the mining coal course because of the advantage of the FLAC^3D for simulating the large deformation event of rock and soil engineering mechanics. The exploit extent is the most less than the size of computational model. The conclusion is obtain that the curve of the subsidence and velocity with the iteration steps is accord with the improved knothe time function for surface subsidence due to underground mining.8) Because of the subsidence of the point on the surface is independent on the space and time, so the model of the whole dynamic subsidence model can be set up by combining the improved knothe time function model with the section function of the surface subsidence basin or the basin model.This new subsidence dynamic model fits well the curve of the observation data of some coal mine. The dynamic model can describe the courve of the subsidence, incline and curvature when the curve of the section is certain.