Repeated swelling-shrinking behaviors of red-bed mudstone poses a potential threat to high-speed railways. Through swelling test and dry-wet cycle test, the deformation law of mudstone samples was discussed. Using X-ray CT scanning, MIP and BET technology, the inner relationship between deformation and structural characteristics were clarified. The results showed that the surface of sample was chipped and peeled off after two cycles. During the dehumidification, the mudstone has undergone three stages of shrinkage adjustment, accelerated shrinkage and stable shrinkage. Uneven tensile stress caused by evaporation of water molecules in the initial stage of drying delayed the shrinkage. Initial water content was opposite to the changes of stable strain after water immersion and residual strain after dehydration, while it was positively correlated with environmental temperature. Porosity and connectivity keep increasing with the continuous cycle, and the number appeared to gradually descend from the two ends to the middle in space. Successive drying and wetting promoted a wider range of diameter-length ratio by the swelling of hydrophilic minerals and uneven shrinkage stress. Spatial orientation also transitioned to the polar angle. Specifically, the structure evolved from the layered shape to the tree-like and net-like in order. Microscopic scale mainly included uniform flat pores and wedge-shaped capillary pores, ranging from 10 to 80 Å. The number of cycles didn’t affect the morphology of micropores, but only caused volume and specific surface area to enlarge. The existence of clays generated irreversible deformation of micropores and initiated the gradual extension. This work will provide key data and necessary methods for the geohazard problems.

Taking the dolomite with anhydrite interlayer at the bottom of Huangcaoshan Tunnel in Shanghai-Wuhan-Chengdu high-speed railway as the research object, the wetting deterioration and uniaxial compression tests were performed to study the influence of different interlayer orientations on the hygroscopic deterioration characteristics of rock and to analyze the process of rock deterioration. The wetting cracking and deformation characteristics of dolomite with interlayer in different directions were analyzed respectively from the time effect of rock micro-expansion and the change of ultrasonic longitudinal wave velocity, and the uniaxial compression evolution process of samples with different moisture absorption conditions and interlayer directions was analyzed respectively from the aspects of crack volume strain and energy dissipation. The results show that the direction of interlayer had a significant effect on the wetting and deterioration of the rock. The sample with vertical interlayer cracked obviously during wetting, resulting in volume expansion along the axial and radial directions of the sample; However, the sample with horizontal interlayer had almost only axial volume expansion, and the expansion rate was small. After the rock was wet and deteriorated, the propagation velocity of ultrasonic longitudinal wave in the rock decreased, and the decrease amplitude in the sample with vertical interlayer was greater than that in the sample with horizontal interlayer. After rock wetting, its uniaxial compressive strength, crack initiation level, expansion level, and the threshold value of elastic strain energy density for failure decreased, while the radial peak strain, the energy conversion rate of dissipation increased, and the plastic characteristics of the sample were enhanced, and the sample with vertical interlayer changed significantly compared with the sample with horizontal interlayer.