Study On The Stability Of Mine-out Area Close To The Xiaolangdi Reservoir

In this thesis, the mined-out areas of Xin'an mine, around the flood areas of the Xiaolangdi reservoir was considered the background for our model. The stability of overlying strata influenced by mined-out areas under dipping, scouring and dissolution by the reservoir water, and the laws of face movement & deformation and destruction were studied.After testing the mechanical characteristics of coal and rock in saturation within the reservoir area, the mechanical parameters of surrounding rock in saturation, and the relation curves between shear strength of coal samples with various water contents and vertical stress were obtained, which provided data for the similar material simulation and numerical analysis of mined-out areas in the reservoir area.Considering a mined-out area in wangjiagou village of Xin'an County to be the prototypical condition, the similar material simulation has developed a hydrodynamic simulating coal-seam mining system to simulate the laws of movement & deformation of overlying strata with different mining scales, and the surrounding rock reactivation of the mined-out area, which would take place when the mined-out area was under scouring and dissolution repeatedly, and the granules from sidewall and safety pillar were washed away. To achieve accurate displacement observation, the digital camera was used, and a fine deformation displacement analyzing software (named CPAnalysis) was developed to do processing work after data collection. The fractal geometry theory was applied to analyze the rock fracture developing differences of the three-zone in goaf after the first roof collapse, as well as in the second activation of roof surrounding rock. Moreover, the correlative relationship between the subsidence coefficient and fractal dimensions of overlying strata was established.The stability of overlying strata in the mined-out areas in wangjiagou village was studied by numerical simulation. Based on the face topography and accumulation conditions of the underground mined-out areas in wangjiagou village, using the automatic defined functions of FLAC3D, a 3D calculating model was set up. The movement of both overlying strata and surface before and after impounding was simulated, and the strata movement & deformation laws of mined-out areas under seepage were acquired.Based on the cusp catastrophe theory, the stability of mined-out areas in various forms and energy release mechanism when the stability was losing were analyzed. The mined-out areas close to the xiaolangdi reservoir area were assorted. The ones supported by narrow coal (rock) pillars were simplified into mechanics model in dissymmetric mining. While the ones whose spans were almost equal and also supported by narrow coal (rock) pillars were simplified into mechanics model in symmetric mining. Besides, the ones with broad coal pillar supports were simplified into mechanics model in strip-pillar mining. Based on simplified mined-out areas considering the roof, coal pillar and bottom of the model as a system, and bring in water weakening functions, the stability of mined-out areas under penetration and softening effect was studied.