No abstract

Red-bed soft rock in the drawdown area on bank slopes of landslide easily disintegrates upon exposure to water, and its properties experience comprehensive deterioration, which will cause bank slope instability. To better study disintegration mechanism of the red-bed soft rock, a series of laboratory tests were conducted in this paper to investigate the disintegration characteristics, durability and hydrogeochemical process of red-bed argillaceous siltstone under drying-wetting cyclic conditions. Experimental results showed that, with increasing number of drying-wetting cycles, red-bed argillaceous siltstone gradually disintegrated, from initial appearing the cracks on the surface of the samples to large particles gradually breaking up into small fragments. Significant changes in grain size distribution, and the durability index of the samples progressively decreased. Microstructural analysis showed that the size and distribution of pores and cracks in the sample surface significantly increased, such that the sample surface became disordered and complicated. Notable changed in concentrations of ions in the soaking solutions indicated continuous mineral dissolution and loss during the cyclic drying-wetting. Based on the results obtained from the experiment, it is concluded that the disintegration of samples undergoing drying-wetting cycles was the result of the synergistic action of water and temperature. To be specific, the dissolution of calcite, albite, gypsum, montmorillonite and kaolinite during the wetting procedure, which promotes the decrease in mineral content and increases in pores and cracks. The increases in temperature and the dehydration shrinkage of sample during the drying procedure accelerated the disintegration of the samples.

The red-bed rocks were chosen and studied by using uniaxial compressive experiment and scanning electron microscopy to investigate the effect of drying-wetting (D-W) cycles on the mechanical properties and microstructural characteristics of red-bed rock. Additionally, the energy mechanism of specimens subjected to drying-wetting cycles was also explained. Experimental results showed that, the stress-strain could be divided into four characteristic stages in the compression failure process. After subjecting to cycles of D-W, the stress-strain curve gradually changed from softening to hardening. At the same time, uniaxial compression strength (UCS) and elastic modulus dropped obviously, while Poisson’s ratio gradually raised. Microstructural analysis results indicated that the microstructure of the specimen surface was no longer dense and uniform, and the porosity of tested specimens significantly increased with D-W cycles increasing. As the porosity grew, UCS and elastic modulus gradually declined. According to the first law of thermodynamics, the process of rock failure was an event of energy transfer and conversion. As the number of D-W cycles increased, the energy density of specimens all present linear fell. From the perspective of the theory of energy dissipation, the dissipated energy was essential for rock failure, and closely related to the strength of the specimen. With D-W cycles increasing, the specimens were more prone to failure, and the dissipated energy required for failure decreased gradually.