Abstract:
Based on the engineering background of lining structure subjected to cyclic dynamic disturbance and freeze-thaw (F-T) cycle during tunnel excavation in cold area, the cyclic impact compression tests of F-T damaged concrete-sandstone combination were carried out. The effects of rock layer thickness ratio and F-T cycles on the pore size distribution, stress wave shape, peak stress, deformation and failure characteristics and micro-morphology of composite were studied. In addition, a composite damage variable, which could consider the effects of F-T cycle and cyclic impact, was defined based on the variation of longitudinal wave velocity in the present study. Results showed that with the increase of rock layer thickness ratio, the number of micropores decreased while the number of medium pores increased significantly, meanwhile, both the number of anti-cyclic impact times and the peak stress increased gradually. With the increase of cyclic impact times, both theincrease of F-T cycles, the failure mode of the composite specimen gradually evolved from single main crack to multiple cracks, the internal damage of rock and concrete layers was intensified, and both the number and size of micro-cracks and pores in concrete layer were obviously higher than that in rock layer. Obvious intergranular cracks and transgranular cracks were observed in rock layers, however, no obvious damage occurred at the interface of the above two materials. The damage thresholds of concrete, sandstone and concrete-sandstone composite specimens increased gradually with the increase of F-T cycles.