Moisture-absorbing expansion and cracking characteristics of central Sichuan red-bed mudstone based on digital speckle correlation method

Using self-absorption tests combined with the digital speckle correlation method (DSCM), we investigated the evolution of the deformation field, expansion anisotropy, full-field strain, crack development, and deformation mechanisms in mudstone. During the early moisture-absorbing stage, the displacement field was uneven, accompanied by crack initiation and propagation. By the end of moisture absorption, the horizontal displacement exhibited an approximately 45° zonal pattern along the x-axis, while vertical displacement showed a horizontal zonal distribution. The anisotropy degree of the expansion rate over time mirrored the water absorption curve of mudstone. A three-piecewise linear model was developed to fit the relationship between expansion rate anisotropy and water absorption. Throughout moisture absorption, the average linear strain variation followed the water absorption trend, with the final mean linear strain significantly decreasing as sample height increased. The maximum ε_xx occurred at the crack tip, and the strain localization band distribution indicated crack development. The maximum ε_yy aligned with mid-span theory, showing zero vertical displacement. Deformation of mudstone during moisture absorption involved both pore water adsorption and the expansion of clay minerals within the matrix. This study introduces a novel method for examining the hygroscopic expansion and cracking behavior of red-bed mudstone, providing crucial insights into disaster mechanisms and engineering stability in red-bed regions.