Abstract: A combined model of surrounding rock and backfill was designed to simulate the failure evolution of backfilled mining stope. Cyclic loading and unloading tests were conducted on model specimens of three different rocks (marble, granite, and basalt) by using RLW-3000 microcomputer-controlled shear creep test machine under varying lateral pressure; VIC-3D non-contact full-field strain measurement system was employed to simultaneously monitor the damage process and failure of the combined model. Analysis result demonstrates that backfill enhances the integrity and strength of surrounding rock; the combined model undergone a volume dilatation process. The stress-strain curves of the loading and unloading in every cyclic loading process are non-coincident, forming plastic hysteresis loops which becomes more remarkable with the increase of rock’s softness. Strain field approximates uniform field under low cyclic load, while changes between non-uniform field of loading and uniform field of unloading under the condition of high load, exhibiting features of strain localization. Tensile strain firstly appeared in the region of backfill body of low strength, and gradually moves towards two sides of surrounding rock with the climbing of loading. The deformation and failure of backfill body and surrounding rock are asynchronous in spatial-temporal evolution with different failure modes. The failure mode varies with surrounding rock type: rock of low strength exhibits shear failure, and rock of high strength, tensile failure. The results suggest that the evolution of strain field could well reflect the fracture process of the combined model of surrounding rock and backfill.

Key words: filling body, surrounding rock, strain field, combined model, cyclic loading and unloading, fracture mechanism