# Static Properties of Kaolinite Samples from Different Structures and the Influence of Strain Rate
## 4 Determination of Strain Rate and Experimental Details
### Effects of Strain Rate on the Static Properties with Different Structures  
As shown in Figure 11a, when the strain rate increases, the response speed of the pore pressure decreases. The pore pressure response curves at strain rates of 0.012 and 0.005%/min were similar, indicating that the pore pressure of the flocculated samples could fully respond at a strain rate of 0.012%/min. Figure 11b shows the development of pore pressure with axial strain under different strain rates for the dispersed samples at an effective confining pressure of 200 kPa. The overall pattern is similar to that of the flocculated samples. The pore pressures of the dispersed samples also fully responded at a strain rate of 0.012%/min. Compared with the flocculated samples, the pore pressure response of the dispersed samples was much slower at a strain rate of 1%/min. In the triaxial undrained shear tests, the pore water pressure is typically measured from the base, as shown in Figure 4. The permeability coefficient of the dispersed sample in vertical direction is much smaller than that of the flocculated sample. A shear rate of 1%/min is too high for the dispersed sample, when the stain rate is too fast, the pore pressure at the top of the sample cannot diffuse to the bottom quickly. In this case, the pore water pressure measured at the bottom cannot represent the actual pore pressure of the sample. The strain rate has a major impact on the development of pore pressure in the clay. A lower strain rate provided sufficient time for the diffusion of pore pressure throughout the sample, preventing an uneven distribution of water content in the sample. In this case, the pore pressure measured at the instrument base reflected the true pore pressure of the sample. When the strain rate was 0.012%/min, the pore pressure of both the flocculated and dispersed samples fully responded, which also indicates that the pore pressure measured under the three standard strain rates was close to the true pore pressure. Figure 12 shows the deviatoric stress-axial-strain curves for the flocculated and dispersed samples under different strain rates. For the flocculated samples, the corresponding peak deviatoric stresses under strain rates of 0.005, 0.012, 0.05, and 1%/min is 115.64 kPa, 120.53 kPa, 123.62 kPa, and 127.70 kPa, respectively. At the same axial strain, the deviatoric stress increased as the strain rate increased. The peak deviatoric stress at a strain rate of 1%/min is approximately 10% higher than that at a strain rate of 0.005%/min. The initial development of the deviatoric stress in the dispersed samples was faster than that in the  
Figure 10: Repetitive test outcomes. flocculated samples. For the dispersed samples, the corresponding peak deviatoric stresses under strain rates of 0.005, 0.012, 0.05, and 1%/min is 120.20 kPa, 122.27 kPa, 126.47 kPa, and 96.47 kPa, respectively. It can be observed that the faster the strain rate, the smaller the axial strain value required to reach the peak deviatoric stress. The peak deviatoric stress at the strain rate of 0.05%/min was approximately 5% higher than that at the strain rate of 0.005%/min. Similarly to the flocculated samples, the peak deviatoric stress in the dispersed specimens increased with the strain rate. Figure 11: Pore pressure–axial-strain relationships: (**a**) flocculated and (**b**) dispersed samples. Figure 12: Cont. It is worth noting that when the strain rate was 1%/min, the peak deviatoric stress of the dispersed structure specimens decreased. A strain rate of 1%/min is too high for the dispersed sample, and under this strain rate, the pore pressure does not have sufficient time to transmit. This phenomenon was also observed by [PERSON] et al. [9] and [PERSON] et al. [32] who suggested that the postponed dissipation of excess pore water pressure under rapid shear conditions, which cause peak stress ratio would decrease with increasing strain rate. Based on SEM images, MIP tests, it was evident that the dispersed samples had small and closed pores.