Fig. 5 Permeability coefficient of the sheared specimen under different
normal stresses.
As shown in the cross-sections of the sheared specimen in Fig. 6, a
visual distinction between the dry and wet samples was observed, where
mudstone_3 presented more interparticle pores than mudstone_6.
Although the crushing character of the shear band was found in the
particle size distribution, where the content of the 2~1
mm grain size in the middle of the specimen was higher than those in the
upper and lower parts. The dry specimen showed limited fragmentation
under shearing and compression, which was reflected in the absence of a
thin crushing zone after the ring shear tests (Fukuoka et al., 2007;
Kimura et al., 2018). Therefore, the confined water could flow through
the macropores and across the shearing zone easily. In contrast, the
macropores of the wet specimen were filled with mud and almost
disappeared. The particle content finer than 2~5 mm was
increased throughout the specimen of mudstone_6 under wet conditions
and a normal stress of 800 kPa. Similarly, extensive crushing in the
middle part of mudstone_6 was revealed via the further increase of
finer particle content, resulting in the strain softening behavior of
weathered mudstone granules under wet conditions. The difference in the
finer particle content between the dry and wet conditions supported the
variation in the macropores observed in the cross-sections.