Rapid reduction in the shear resistance and permeability of soft
interlayers within a limited shear displacement under water weathering
The activation of landslides and shallow faults is related to the shear
behavior of soft interlayers during groundwater infiltration. Regarding
the water sensitivity of clay minerals, the shear behavior of soft
interlayers may rely more on weathering and water content than the
requirement of shear displacement and normal stress for quartz grains.
Here, we present the reduction characteristics of the shear resistance
and permeability of mudstone granules considering weathering under
dry-wet cycling. Within a shear displacement of 20 mm, the shear mode
transformation of the weathered mudstone granules from strain hardening
to strain softening was revealed from dry to wet conditions. However,
this transition was not observed for unweathered mudstone and weathered
sandstone samples. Correspondingly, the permeability perpendicular to
the shear zone reduced 10~45 times with increasing
normal stress according to post-shear measurements. Because weathered
particles exhibited more micropores, the addition of water resulted in
mineral separation and generated mud that filled the specimen pores.
Thus, the sealing and lubrication effect of the mud decreased the
porosity and shear resistance of the soft interlayer, along with
increasing particle roundness. This rapid transformation mechanism
within a limited displacement reveals the effect of water softening and
weathering on the shear behavior of soft interlayers, which helps to
understand landslide occurrence and shallow fault activation.