Abstract: To investigate the meso-damage evolution characteristics of rock under different drying-wetting cycles, a series of drying-wetting cycle experiments was conduct on saturated argillaceous sandstone from a slope in Three Gorges Reservoir. Low field nuclear magnetic resonance(NMR) was used to test the damage behaviors of the sandstone subjected to drying-wetting cycle. The amplitude of NMR T2 spectrum significantly changed under the influence of the drying-wetting cycle. With increasing drying-wetting cycles, the peak stress of argillaceous sandstone decreased exponentially, and the T2 spectrum area and porosity showed exponential increase. The internal pore of rock increased gradually, and the pore size increased, finally small cracks coalesced and extended gradually. The final cracks distribution of MRI of specimen were similar to the SEM ones under different wetting-drying cycles. The gray value distribution of the pixels in MRI coincided with logarithmic Gauss distribution, and the expectation of the distributions was gradually saturated with drying-wetting cycles. As the number of cycles increased, the mechanical parameters gradually decreased, and the decrease of peak stress was positively correlated with the increase of porosity.

Key words: argillaceous sandstone, drying-wetting cycle, nuclear magnetic resonance (NMR), magnetic resonance imaging (MRI)