Study On Roof Damage Rule Of Underground Goaf

There are a large number of underground goafs left by mining operations,and their existence poses significant harm.The instability of the overlying rock in the goaf has been a research hotspot in the field of geotechnical and mining engineering.Studying the damage and failure law of the roof in underground goafs is of practical significance to control goaf stability and surface subsidence.Aiming at the problem of roof damage and failure law in underground goafs,according to the theory of elastic thin plate,the uniaxial press is used to carry out continuous loading and periodic loading on the roof model of underground goafs,and the acoustic emission test system is used to study the acoustic emission activity characteristics in the process of roof damage and failure in goaf,finally,the finite difference numerical simulation of roof damage process in goaf under continuous loading and periodic loading is carried out.The following conclusions are obtained :(1)Through the study of continuous loading experiments on the roof of the underground goaf,it was concluded that the roof of the goaf experienced three stages:compaction,linear elastic deformation,and failure deformation under continuous load.The macroscopic failure of the roof of the goaf occurred in the third stage,and the cracks generated in the central area of the roof gradually spread to the side walls and the top angle.(2)Through the study of periodic loading experiments on the roof of the underground goaf,it was concluded that the roof of the goaf under periodic load experienced three stages of initial failure deformation,stable failure deformation,and accelerated failure deformation.The deformation rates of the three stages were high speed,low speed,and high speed,respectively.Cracks were generated in the corner of the roof and gradually spread to both sides,and the roof eventually collapsed as a whole.(3)Through the study of acoustic emission monitoring experiment of roof failure in underground goaf,the results of acoustic emission monitoring are in line with the law of roof damage and failure in goaf under continuous load and periodic load.The obvious Felicity effect appears in the roof of goaf during the periodic loading process,the Felicity ratio can be used to judge the severity of the damage to the roof of goaf.A cusp catastrophe model was established to characterize the damage degree by cumulative acoustic emission energy count,the cumulative acoustic emission energy count experienced a relatively gentle initial stage,a stable stage and a steep rise instability stage,and the damage mutation point appeared in the early stage of the instability stage.(4)Through the study of numerical simulations of underground goaf roof stability,the change of internal stress of the goaf roof in the process of continuous and periodic loading was analyzed.The performance of roof stress concentration was consistent with the physical model experiment of the goaf.The roof of the goaf is prone to two failure modes: tensile failure from the central area or expansion from both ends to overall collapse.In practical engineering,the roof control of goaf should take corresponding supporting measures in the center and both ends of the roof.