Mechanism Research On Shear Fracture Of The Combined Model Of Backfill Body And Surrounding Rock

According to the actual condition of the filling mine, the combined model of backfill body and surrounding rock was designed. The failure process of the combined model under shear loading was studied by using VIC-3D non-contact full field strain measurement system, infrared monitoring system, acoustic emission(AE) system, rapidly photographing and some other monitoring systems. Shear fracture evolution characteristics of the combined model under different cement sand ratio of backfill body and different normal stress were discussed. The main results were as follows:Through the analysis of the shear strength and deformation characteristics of different test conditions, indicated that with the increasing of normal stress, the peak stress of shear fracture was larger, the shear strain value was smaller. The Failure of the combined model was mostly presented goose fracture mode. Firstly, cracks were produced on both sides of the surro unding rock of the mining field, and then, with the increasing of the load, the cracks extended to the surrounding rock of the active pressure surface and the surrounding rock of passive compression surface.Based on infrared radiation effecting of co mbined model under shear load, the evolution characteristics of the model surface average infrared radiation temperature(AIRT) and infrared thermal image with different cement sand ratio of backfill body and different normal stress were studied. The research shows that with the decreasing of the cement sand ratio of backfill body, the changing range of AIRT of the combined model was decreased and the abnormal high temperature precursor of infrared thermography of the combined model was more obvious. With the increasing of stress, the changing range of AIRT of the combined model was increased and the abnormal high temperature precursor of infrared thermography of the combined model was more obvious.Through analyzing of the AE characteristics of the model of different test conditions, the change law of the AE event and AE energy and the characteristics of the distribution evolution of AE source in the shear rupture process were researched. With the increasing of cement sand ratio, the larger and the more lag of the peak value of the AE event rate was, the later appeared of the AE energy peak. With the increasing of normal stress, the larger of the peak value of the AE event rate was, and the longer duration of peak value of the AE event rate was, the larger the AE energy was. The appearance of the peak of the AE event rate and the peak of the AE energy was important precursor information of model failure. The AE source space locating point was first generated in the surrounding rock of the passive compression direction, and then expanded to the symmetry direction, and gradually spread to the shear zone.Based on fractal geometry theory, the fractal characteristics of the AE source space locating points were studied. The damage fractal dimension calculation program was written, damage fractal dimension of each stress stage were calculated. The change of the stage fractal dimension corresponded well to the formation and expansion process of the internal micro cracks in space of the model. At the early stage, the stage fractal dimension increased with the increasing of the stress, and the dimension of the stage fractal dimension appeared near peak stress. The cumulative fractal dimension increased with the increasing of the stress. In the prediction of the failure of rock mass, slowing down of the stage of fractal dimension and slowing down of the rising speed of the cumulative fractal dimension all can be precursor information.