Fig. 6 Particle size distributions of a sheared specimen (left)
corresponding to each layer of a cross-section (right).
3.3 Micropore increases for the weathered mudstone
granules
The ESEM images in Fig. 7 suggest that the microstructure of the
mudstone samples varied with the number of dry-wet cycles. At low
magnifications (200 μm and 500 μm), mudstone_0 had no significant
microstructure at the particle boundaries, which was the same as that
observed in the interior of the particles. The mineral arrangement was
relatively consistent according to the homogeneous grayscale, indicating
a lower surface roughness for mudstone_0 than for the weathered
particles. After the dry-wet cycling treatment, several micropores of
approximately 80 μm were found at the particle boundaries in
mudstone_3. Many more micropores (approximately 50~300
μm) were observed from the boundary to the inside of the particles in
mudstone_6, due to the further development of water-rock interactions.
Analogously, at the high magnification (mineral scale), there was almost
an absence of cracks and micropores in mudstone_0, while the direction
of mineral arrangement was fairly consistent. This kind of homogeneity
demonstrated that the mudstone samples without dry-wet treatment were
undamaged. On the other hand, the mineral distribution of the weathered
granules was disordered, resulting in a higher roughness than that
observed for mudstone_0. Thus, the damage feature from the boundary to
the inside of particles may be based on the micropore evolution process
during dry-wet cycling (Fig. 7).