Stability Analysis Of Old Empty Area After Shallow Multi-Coal Mining And Study On Grouting Filling Treatment Technology

Under the background of accelerating expansion of urbanization in China,It is inevitable to use the underlying goaf site as the foundation of the building.Taking the stability of the ground surface of the goaf formed by the mining of multiple coal seams in the Mentougou mining area in Beijing as the research background,comprehensively using numerical simulation,on-site monitoring and theoretical analysis methods,the vertical stress,surface movement and deformation laws of slice mining of the old goaf mining(faced with the risk of illegal mining)are studied.And putting forward the prevention and control technology of grouting to fill the goaf,so that it can improve the stability of surface buildings.The main conclusions are as follows:Geophysical prospecting shows that there are still signs of illegal mining in the construction land.Numerical simulation analyzes the surrounding rock structure and stress field of the stope after mining,and obtains the relationship between the depth of influence of buildings in the old goaf and the caving fissure zone,which has verified the possibility of secondary "activation" in the goaf.In the rock Brazil splitting experiment,the ultimate load-bearing capacity,tensile strength,and speed of crack propagation of coal,mudstone and sandstone increased sequentially,and the propagation time of the through crack in the test piece decreases sequentially.The rougher the coal and rock mass,the better the stability of the overlying rock structure in the goaf.The stability of the sample of the rock mass is controlled by the local weakened area under the combined action of internal and external factors,and it does not start from the traditional point of failure.When the inclination angle of the interlayer of the rock mass is 45-60°,the method of increasing the confining pressure has a better suppression effect on the weakening of the strength and stiffness of the rock specimen.The transitional conditions of the two failure modes of the overburden are deduced,and with the help of the Mohr-Coulomb strength criterion,the overburden strata is divided into four deformation stages:elastic state?compression-shear failure?tension-shear failure?tensile failure.The calculation formulas for the elastic limit bending moment,plastic limit bending moment and the step distance of the collapse of each rock beam of each rock beam of the overlying rock strata in the mined-out area are deduced.The influence of mining again conditions on the stability of the goaf construction site is studied.The moving basin formed by the surface subsidence curve of the inclined observation line is flat-bottomed,and the moving basin formed by the surface subsidence curve of the strike observation line is sharp.However,the maximum value of the horizontal movement of the surface appeared near the open-off cut of the coal seam and the stopping line of the coal seam.By comparing the water-binder ratio,fly ash content,solidification rate,curing age,setting time and other factors and indicators,it is determined that the fly ash content is 70%,and the water-binder ratio is 1:1.2 or 1:1.5.Optimal proportion of filling material in proportion position,determine the strain condition as the judgment condition of the deformation localization of the filling body specimen.The theoretical calculation formula of the actual filling volume is deduced,and the pumping system is constructed.When the load size and location of the proposed building above the goaf are the same,the residual subsidence of the curved subsidence zone of the goaf is not only greater than the residual subsidence of the fractured zone but also greater than the residual subsidence of the caving zone of the goaf,the bending sinking zone is most affected by the load,and the residual subsidence of the inner edge of the building foundation is greater than the outer edge.After filling,the building foundation of the underlying goaf is basically in a relatively stable state.When the mining disturbance and the energy input for the activation of the goaf exceed the energy that the building can withstand,the building will generate damage and plastic dissipation energy,and exchange energy with the outside to ensure the building system not to be destroyed.The paper has 113 pictures,20tables and 132 references...