FIGURE 3 Sample preparation and size (a) Interfacial sample, (b) Constant temperature process

2.4 Testing Device

Due to the strong water-heat sensitivity of frozen soil, a constant normal stiffness direct shear apparatus (Figure 4) was used to conduct interfacial characteristics research in order to better control the experimental temperature. The direct shear apparatus was first installed in a thermostat with a temperature control accuracy of ±0.2℃, and then the thermostat was placed in a freezer with a temperature control accuracy of ±0.5℃. This two-level temperature control system achieved good temperature control accuracy.