# Static Properties of Kaolinite Samples from Different Structures and the Influence of Strain Rate
## 4 Determination of Strain Rate and Experimental Details  
As mentioned previously, the selection of the strain rate has a major impact on the shear strength of the clay. Additional research is needed to determine the strain rate when comparing the effects of structure on the [PERSON] properties of kaolin clay. In the past, various scholars have chosen varying strain rates. [PERSON] and [PERSON] [28] suggested that the minimum duration for shearing clay should be 2 h. [PERSON] and [PERSON] [25] proposed a method to determine the strain rate, with the shear time varying depending on drainage conditions based on Equation (1). The method used to determine shear time under undrained conditions is shown in Equation (2). The strain rate was calculated as the estimated failure strain divided by the shear time (Equation (3)). Other internationally recognised standards for determining strain rate include the American Society for Testing and Materials (ASTM, 2015) [29] and British standards (BS, 1990) [30]. The formulae for calculating the strain rate based on these two standards are listed in Table 3. Combining these strain rate calculation formulas reported in previous studies, this study integrated the Germaine and [PERSON] formula, ASTM 2015 and BS 1990 standards to determine the strain rate of the flocculated and dispersed samples. In Equations (1)-(5), \(\dot{\epsilon}\) represents the strain rate, \(t_{\text{f}}\) is the shear time, \(\epsilon_{\text{f}}\) is the estimated failure strain, and \(t_{\text{x}}\) is the time required for the \(x\%\) consolidation stage (e.g., \(t_{50}\) is the time required for the 50% consolidation stage). F is a parameter related to the drainage conditions during the consolidation process. In this test, the consolidation drainage conditions were radial drainage and one end; the F-value of F is 1.8. [PERSON] and [PERSON] [31] suggest that the pore pressure can adequately respond to the strain rates determined by the ASTM and BS standards. \[t_{\text{f}}=16\times t_{100}\;(\text{drainage conditions}) \tag{1}\]  
\[t_{\text{f}}=2\times t_{100}\;(\text{undrained conditions}) \tag{2}\]  
\[\dot{\epsilon}=\frac{\epsilon_{\text{f}}}{t_{\text{f}}} \tag{3}\]  
[PERSON] [21] stated that for flocculated structure samples, the deviatoric stress value remained essentially unchanged and stable after the strain reached 5%, whereas for dispersed structure samples, strain softening occurred when the strain exceeded 5%; therefore, the failure strain was estimated to be 5%. Figure 7 shows the relationship between the drained volume and time during the isotropic consolidation stage for the flocculated and dispersed structure samples under an effective confining pressure of 200 kPa. Based on these findings, \(t_{100}\) and \(t_{50}\) were obtained, and the strain rate results under different standards are summarised in Table 4. The strain rates determined by the three standards for the flocculated structure samples ranged from 0.011% to 0.013%, 0.005%, and 0.0056% for the dispersed structure samples. The strain rate values determined by the three standards are very close; the strain rates for the flocculated and dispersed structure samples were found to be 0.012%/min and 0.005%/min, respectively. Referencing the strain rate choices of other scholars, we ultimately adopted four strain rates: 0.005, 0.012, 0.05, and 1%/min. Cylindrical specimens (Diameter = 50 mm; High = 100 mm) extracted from the core of the reconstituted sediment were used for the triaxial undrained shear test. After it was placed on the pedestal, the specimen was circulated with de-aired water from the bottom to the top, followed by the application of back pressure. Only when the Skempton pore pressure coefficient is greater than 0.96 can the sample be considered saturated.