Rapid reduction in the
shear resistance and permeability of soft interlayers within a limited
shear displacement under water weathering
Guoqing Chen*1; Tao Wei1; Lei
Wu1; Fangzhou Liu2
1. State Key Laboratory of Geohazard Prevention and Geoenvironment
Protection, Chengdu University of Technology, Chengdu, China ; 2.
Department of Civil and Environment Engineering, University of Alberta,
Edmonton, Canada
Abstract: 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.
Key words: Weathered soft interlayer;
mudstone granules; shear behavior;
permeability; dry-wet cycle.