FIGURE 2 Mortar block sample preparation process (a) Material
preparation, (b) Mixing, (c) Pouring into the mold and
vibrating/smoothing, (d) Curing, (e) Demolding, (f) Measuring dimensions
2.3 Interfacial sample
After naturally air-drying the soil samples collected on site and
passing them through a 2mm sieve, they were thoroughly mixed to ensure
homogeneity. The initial water content was determined using the
oven-drying method, and then a certain amount of water was added to
achieve wet soil samples with water contents of 10%, 13%, and 16%.
These samples were placed in sealed bags and allowed to stand for 24
hours to ensure uniform water content distribution. A mortar block was
placed on the lower side of the sample mold, and wet soil with a
compaction of 95% was weighed and compacted in three layers into the
mold until level with the top edge of the mold box. The size of the test
sample was 100mm×100mm×50mm (Figure 3a). The test sample consisted of
two layers, with the mortar block being 25mm tall, and the soil layer on
top and the mortar block below. This configuration placed the shearing
interface exactly in the middle and aligned with the upper and lower
shear box interfaces of the direct shear apparatus, enabling better
study of the mechanical properties of the interface during the shearing
process. After preparing the direct shear samples, they were wrapped in
plastic wrap, and the bottom and sides were further wrapped with
insulating material and placed in a constant temperature chamber (Figure
3b). The temperature of the chamber was adjusted to the target test
temperature and maintained for 24 hours to complete the freezing of the
direct shear samples.