Rapid reduction in the shear resistance and permeability of the weak layer in the evolution of water-rock weathering

• Published in: Engineering geology 2022-03, Vol.299, p.106545, Article 106545
• Main Authors: Wei, Tao, Chen, Guoqing, Wu, Lei, Liu, Fangzhou
• Format: Article
• Language: English
• Subjects: Dry-wet cycle; Mudstone granules; Permeability; Shear resistance; Weak layer
• ISSN: 0013-7952; 1872-6917
• DOI: 10.1016/j.enggeo.2022.106545

The activation of landslides and shallow faults is related to the shear behavior of weak layers during groundwater infiltration. Regarding the water sensitivity of the weak layer in the weathering process, shear softening for weak layers that relies more on damage properties and water content than the requirements of shear displacement and normal stress for quartz grains remains enigmatic. Here, we present the reduction characteristics of the shear resistance and permeability of mudstone granules considering weathering through a dry-wet cycle. Within a shear displacement of 20 mm, the shear mode of the weathered mudstone granules transformed from strain hardening to strain softening when switching from dry to wet conditions. Correspondingly, the permeability perpendicular to the shear zone decreased 10– 45 times with increasing normal stress according to postshear measurements but was not observed for unweathered mudstone and weathered sandstone samples. This was attributed to the insufficient particle crushing of debris in the shear band and low content of fine particles in the macropores. Because weathered particles developed more micropores, the addition of water resulted in clay mineral separation and generated mud that filled the macropores. Thus, the sealing and lubrication effect of the mud rapidly decreased the porosity and shear resistance of the weak layer with increasing particle roundness and uniformity. This transformation mechanism within a limited displacement reveals the effect of water and weathering on the rapid shear softening of weak layers, which helps understand landslide occurrence and shallow fault activation. •Strain-softening for the wet weak layer is appeared within a shear displacement of 20 mm.•10– 45 times permeability reduction is found for wet specimens with increasing normal stress.•Rapid argillization of the weak layer explains the activation of landslides and shallow faults.