Experimental Study on Anisotropic Deformation Behavior and Microstructure Evolution of Red-Bed Mudstone

A detailed exploration about the development of the microscopic behavior of red-bed mudstones and exploration of their anisotropic deformation mechanisms in-depth can help to optimize the improvement of red-bed subgrade. To discuss the effects of single immersion and dynamic wetting-drying cycles, the Aramis system was used to monitor the mudstone deformation, whose results were compared with results of conventional deformation tests; the patterns of moisture migration was analyzed. Variations in mineral compositions, particle orientation and pore characteristics during cycles were investigated. The results show that after encountering water, red-bed mudstones swelled in axial and shrank in radial; the swelling first started around the initial fissures. During wetting-drying cycles, the decrease of equivalent montmorillonite content leads to the weakening of water absorption capacity and deformation capacity of the red-bed mudstone from the sixth wetting-drying cycle; moisture migration causes a directional shift of mudstone particles towards the direction of moisture migration, which triggers anisotropy of the red-bed mudstone deformation; moreover, wetting-drying cycles lead to the increase of pores and fissures inside the red-bed mudstone, with a more complex morphology and the increase of scattered detrital particles, which are the main reasons for the continuous deformation of the red-bed mudstone.