Plain language summary
The shear strength and shear-induced permeability variation of soft
interlayers are significant for occurrence of landslide and activation
of shallow fault. Their properties are related to the shear rate and
displacement, effective normal stress and water content, particle size
distribution and mineral composition. Different from the hard grains as
quartz, the sensitivity of mudstone to water induces the layered rock
mass fracturing and softening into finer fragments. Although with a wide
range of particle size distribution, rapid reduction of shear strength
and permeability for the soft interlayer when encountered water has
triggered catastrophic landslides disaster. How this softening behavior
happening is practical significance. Here, we present that the weathered
mudstone granules tend to transform into mud in wet conditions due to
the increment of micropore after long-term weathering of water. Within a
limited shear displacement, wet granules could trigger the reduction of
shear strength and permeability, which deepens our understanding of soft
interlayers in slope stability and fault activation when groundwater
infiltrates.