Experimental study on the damage and failure mechanism of freeze-thaw filled fractured sandstone under uniaxial compression

In order to study the uniaxial compression damage and fracture mechanism of filled fractured sandstone under different freeze-thaw cycles, the uniaxial compression test of filling fractured sandstone under different freeze-thaw cycles, uniaxial compression tests of filled fractured sandstone under different freeze-thaw cycles were carried out. This was achieved by combining indoor macroscopic and microscopic tests with acoustic emission(AE), nuclear magnetic resonance(NMR) and CT scanning technology, and the macroscopic and microscopic fracture mechanisms were analyzed. The results show that with the increase of freeze-thaw cycles, the particle spalling at the edge of sandstone is intensified, the mass in a dry state increases first and then decreases, and the loss of longitudinal wave velocity is obvious. The uniaxial compression stress-strain curve is divided into five stages. The peak strength and elastic modulus show a linear decreasing trend with the increase of freeze-thaw cycles. The acoustic emission ringing count shows a change rule of ' low activity-local activity-advanced activity ‘, and the events are concentrated in the middle of the sample and around the crack. The T2 spectrum of nuclear magnetic resonance shifted to the right, the proportion of micropores gradually decreased, and macropores and ultra-macropores appeared, showing a ‘micropore shrinkage-micropore increase-macropore expansion ' chain damage process. The research results can provide scientific support for the evaluation of rock mass engineering stability in cold regions.