Fig. 4 Shear strength parameters (cohesion c and internal
friction angle φ ) of the four kinds of samples. Note:c pd/φ pd representsc and φ at the peak strength of dry samples.c pw/φ pw representsc and φ at the peak strength of wet samples.c rw/φ rw representsc and φ at the residual strength of wet samples.
3.2 Permeability of sheared
specimens
The permeability coefficient of the sheared specimen in Fig. 5 revealed
negative correlations between the permeability and normal stress, and
the permeability and number of dry-wet cycles. A linear reduction in the
permeability coefficient with increasing normal stress was found for all
the mudstone specimens, although the weathered specimens in dry
conditions presented a considerable fluctuation, which may be attributed
to the heterogeneity of particles. Under the softening impact of water,
the permeability coefficient of weathered mudstone granules decreased
sharply with increasing normal stress when compared to the results of
mudstone_0 and was close to 1.0×10-5 cm/s. The
permeability difference between the dry and wet conditions of the
weathered samples varied from 10 to 45 times with increasing normal
stress at a limited shear displacement of 20 mm. Under the wet
condition, a small reduction in the permeability of mudstone_0 was
observed, but its permeability was still lower than that of most dry
specimens. By fitting the data in a linear relation, the reduction in
the slope from dry to wet conditions demonstrated that the change in
permeability induced by the increasing normal stress was decreasing. The
influence of weathering intensity on permeability was lower for
mudstone_3 and mudstone_6 because of the decreasing discrepancy under
wet conditions, while this trend was not apparent in dry conditions. Due
to the low cohesion of the samples, the permeability of the sandstone
was higher than that of the mudstone, so it was more difficult to obtain
the mudstone results under the same test conditions. Thus, the
difference in the permeability coefficient controlled by lithology was
not discussed in this study.