# Creep Properties and Creep Modelling of Guilin Red Clay
## 2 Materials and Methods
### Triaxial Shear Test Method and Results  
A triaxial shear test was performed according to the \"Standard for geotechnical testing method (GB/T50123-2019)\". According to the moisture content and dry density in Table 1, to make a sample (Figure 3 left), the sample production was completed after reaching the pump saturation requirement. Then, the sample was loaded into the test apparatus for the \(B\) test (\(B=\Delta u/\Delta\sigma_{3}\), where \(\Delta u\) is the pore pressure change and \(\Delta\sigma_{3}\) is the cell pressure change). When \(B\) > 0.95, the sample was fully saturated, and conversely, the sample was saturated with the counter pressure of the sample until a value of \(B\) > 0.95 was reached. The saturated samples were subjected to consolidated undrained shear tests at cell pressures of 100 kPa, 200 kPa, 300 kPa, and 400 kPa, respectively, at a shear rate of 0.08 mm/min, and  
Figure 1: Grain size distribution curve of red clay.  
Figure 2: Triaxial test equipment: 1, cell pressure and back pressure controller; 2, axial pressure controller; 3, pressure chamber; 4, data collector; and 5, computer control systems.  
the test procedure is shown in Figure 3. The stress-strain curves obtained from the triaxial shear tests are shown in Figure 4.  
It can be seen from Figure 4 that a large deformation occurs after applying deviatoric stress in the initial stage of shear. This is due to the existence of large pores and microscopic pores between soil particles and soil particles inside the sample These pores are connected with each other, which makes the pore water flow phenomenon occur inside, and this kind of structure easily causes the sample to produce a large deformation after applying deviatoric stress. As the axial load increases, the soil particles are gradually compacted; if the soil skeleton is to be further compacted, the axial stress required per unit strain gradually increases, and the ability of the sample to withstand external loads increases. However, during the deformation of the sample, structural fractures occurred, which resulted in a weakening of the connectivity between the soil particles and a weakening of the cementation capacity of the red clay. This structural damage affected the shear resistance of the red clay, causing the stress-strain curve to gradually flatten.  
From Figure 4, it can be seen that when the red clay is subjected to consolidated undrained shear, the stress-strain curve shows a continuous hardening type. The destructive deviatoric stress is taken as the deviatoric stress corresponding to an axial strain of 15%, the cell pressures are 100 kPa, 200 kPa, 300 kPa, and 400 kPa, respectively, and  
Figure 4: Triaxial shear stress–strain diagram of red clay.  
Figure 3: Triaxial test sample and test process (1. triaxial sample; 2. sample being sheared; and 3. shear damage of the sample).  
the deviatoric stresses required for the destruction of the samples are 287 kPa, 431 kPa, 542 kPa, and 662 kPa, respectively. From the stress-strain curves, it can be seen that as the cell pressure increases, the deviatoric stress required to damage the sample in shear increases. At 400 kPa, the deviatoric stress required to destroy the sample is approximately 2.3 times greater than at 100 kPa. The destructive deviatoric stress obtained from the triaxial test was plotted on Mohr's stress circle with the common tangent line, as shown in Figure 5, which indicates that the cohesion and angle of internal friction of the red clay are 57.20 kPa and 22.47\({}^{\circ}\), respectively.