Analysis Of Cumulative Damage Under Dynamic Loading And Safe Thickness Of Roof Underlying Mined-Out Areas

Reasonable assess the roof stability of the mined-out areas under Open-pit mine, and revealed the roof deformation damage characteristic of the mined-out areas under multi condition, for Open-pit mine safety production provide important fundamental basis is the critical technical problem of engineering practice urgently to be solved. At present the roof of the mined-out areas under Open-pit mine falling and collapse still holds high proportion. The main reasons for roof falling and collapse is the outside construction load disturbance causes the roof damage evolution and the Open-pit mine step down excavation causes roof thickness insufficient, so research in the roof safety thickness of mined-out areas under dynamic load and cumulative damage effect, for avoiding the falling and collapse cause production accident bring potential safety hazard for normal operation of open-pit mine has the important theoretical and practical value. This present paper main research results were summarized as follows:(1) Based on Reissner thick plate theory, combine the engineering practical situation, see the roof of Mined-out area as thick plate and see the Mechanical construction loading as the dynamic load. With the tensile strength of roof strata as control index, derived the calculation formula of the roof of Mined-out area under dynamic load and revealed changing rule of the deformation and tensile stress under different thick span ratio. And analysis the creep characteristics of goaf roof under the low stress conditions.(2) The three-dimensional engineering geological model and computation model was built using FLAC^3D, apply the the Mechanical construction load on the surface of the mined-out regions of different elevation, Then the roof of mined-out areas and pillar damage failure regions were analysed, stress concentration degree, and the ranges of principal stress were discussed, and the failure mode of room-and-pillar mining and roof stability criterion are put forward also. Through these monitoring displacement curves, the deformation and failure process and its damage evolution of the roof in mined-out areas were revealed under mechanical construction loading.(3) Based on blasting vibration velocity obtained by site monitoring, the continuous and equal-time-interval blasting vibrations as normal incidence were exerted for three times on the surface of the mined-out regions. Then the roof of mined-out areas and surrounding rock damage failure cumulative effects were analysed, stress concentration degree, and the ranges of principal stress were discussed also. Through the monitoring displacement curves, the dynamic deformation response characteristic and progressive displacement cumulative effect of the mined-out area and surrounding rock were revealed under repeated blasting vibrations.