# Strain Rate Effect on Artificially Cemented Clay with Fully Developed and Developing Structure
## 4 Discussion  
According to the aforementioned test results, the strain-rate-dependent behaviour of clay, especially with bond structures, was found to be influenced by the presence and patterns of bond structures, inherent viscosity, local drainage during shear plane formation, and roughness of the shear plane. Table 2 summarises previous investigations on the effect of the rate of triaxial shearing on the strength of different types of soil with various soil structure statuses. The positive rate effect on the strength of the OACK observed in this study is in good agreement with the results of previous studies. Figure 6: Negative rate effect of YACK during post-peak shearing stage. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & & & & & & **Rate Effect** & & \\
**Type of Soil** & **Soil Structure Status** & **Shearing Procedure** & **Shear Rate** & **Pre-Peak/Small** & **Post-Peak/Large** & **Mechanism** & **Reference** \\  & & & & & & **Strain** & & \\ \hline \multirow{2}{*}{Belfast day} & OC Undisturbed & Triaxial & 0.05-0.5-5 & Positive & Positive & Shear viscosity & [PERSON] et al. [8] \\  & & SPS & & & & & \\  & & Triaxial & 0.15-1.5-15 & Positive & Positive & Shear viscosity & [PERSON] \& Yin [34] \\  & & NC + OC Recon. & & CRS & & & & \\  & OC Undisturbed & Triaxial & 0.2-2.20 & Positive & Positive & Shear viscosity and smaller excess & [PERSON] \& [PERSON] [53] \\  & & SPS & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\ \hline \end{tabular}
\end{table} 
Table 2: Rate effect of clay soils under triaxial shearing. Since the shear behaviour was dominated by different factors during the pre-peak and post-peak shear stages, after the formation of the shear band on the specimen, it is worth comparing it with the shear behaviour under ring shear. Table 3 summarises previous studies on the rate effect of cohesive soils on residual strength. The reasons for the negative effect observed in the present study during the pre-peak stage are similar, i.e., partially/locally drained, resulting in a 'denser' soil status. The Scanning Electron Microscope (S-4800, manufactured by Hitachi, Tokyo, Japan) tests have been carried out in order to investigate the microstructure of pure kaolin and cemented kaolin. The samples were collected from the shear band area of the specimens after triaxial shearing. The results indicate that the incorporation of cement leads to the formation of a flocculated and aggregated structure, which consequently results in an increase in both the pore size and particle size. Figure 7a clearly illustrates the platy nature of the kaolin particles, with their orientations being randomly distributed. Figure 7b shows the SEM images of the ACK specimens under low confining stress; the platy particles were loosely stacked with larger pores, showing lower compaction, less fragmentation, and no preferred orientation. These characteristics indicate a relatively brittle and sliding shear. In contrast, Figure 7c shows that high pressure leads to tighter particle packing, reduced porosity, increased fragmentation, and slight particle alignment along the shear direction. The shear patterns are more frictional. Additionally, the pore structures evolve from dispersed and larger pores under low pressure to compressed microcracks and sealed pores under high pressure, thereby reducing the permeability.