Characteristics of crack network catastrophe in highly weathered mudstone under hydro-mechanical disturbance: a cross-scale damage constitutive framework.

To thoroughly investigate the patterns of crack development and the mechanisms of degradation damage in shallow, highly weathered mudstone subjected to repeated dry-wet cycles, a series of laboratory tests were conducted. Initially, the progression of surface cracks on the specimens was documented through fixed-point photography. Image processing techniques using ImageJ software were employed, with crack ratio and fractal dimension as evaluation indices, to quantitatively analyze the relationship between fracture development and the dry-wet effect at both macro and mesoscales. Secondly, stress-strain characteristics of mudstone under different numbers of dry-wet cycles were obtained through direct shear tests. Mesoscopic parameters, crack ratio and fractal dimension, were introduced to establish a damage constitutive model for mudstone under the coupled action of dry-wet cycles and loading. The results indicate that both cohesion and internal friction angle exhibit a stepwise degradation pattern with increasing dry-wet cycles. After 9 cycles, the loss rate of cohesion is significantly higher than that of the internal friction angle. Both crack ratio and fractal dimension increase with the number of dry-wet cycles but decrease with increasing compaction degree. After 3 dry-wet cycles, the basic skeletal structure of the cracks has been preliminarily formed, gradually developing into a reticulated crack network. The stress-strain characteristics can be roughly divided into elastic deformation, elastoplastic deformation, and plastic deformation stages. Furthermore, the stress state of mudstone gradually transitions from strain hardening to strain softening with increasing dry-wet cycles. The established meso-damage constitutive model demonstrates a strong correlation with experimental data, effectively capturing the deformation and failure processes of shallow, highly weathered mudstone subjected to dry-wet cycles. Notably, the model exhibits the highest fitting accuracy under low-stress conditions, underscoring its robust applicability in characterizing the deformation and failure characteristics of shallow weathered mudstone in such environments.The research findings provide theoretical references for the optimal design of reinforcement for shallow weathered mudstone cut slopes in practical engineering.