3 Results

3.1 Shear resistance

The direct shear results shown in Fig. 3 demonstrate that the peak shear stress of mudstone granules decreased with an increasing number of dry-wet cycles when tested under both dry and wet conditions. Notably, the variation in the original direct shear data was smoothed with the fast Fourier transform method. Strain hardening behavior was observed for the dry specimens: the shear stress increased rapidly and remained constant near the peak strength without significantly decreasing with increasing shear displacement. Although a wide normal stress range from 200 kPa to 1400 kPa was applied, dependance of the strain softening behavior on the normal stress observed in Ma et al. (2019) was not revealed within 20 mm of shear displacement. With increasing weathering intensity, the drop in the peak shear stress of the dry specimens increased at a higher normal stress. Compared with the mudstone, the sandstone exhibited a greater reduction in the peak shear stress between different normal stresses in the strain hardening curves after 6 dry-wet cycles (Fig. 3 d).