# Strain Rate Effect on Artificially Cemented Clay with Fully Developed and Developing Structure
## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Type of Soil** & **Soil Structure** & **Shearing** & **Shear Rate** & **Rate Effect on** & & \\
**Status** & **Procedure** & **(mm/min)** & **Residual** & **Mechanism** & **Reference** \\ \hline Kaolin clay & Recon. & Ring shear & 0.013-0.13-1.12- & Positive & & Shear viscosity; sliding to turbulent shear with a higher rate & [PERSON] et al. [22] \\ Claystone & Recon. & Ring shear & 0.05-0.92-10- & -400-600 & Negative & Soils with transitional shear & \\ Amber clay & Recon. & Ring shear & 12-60-120-300 & Negative & Healing, broken bonds restoration at a lower rate & Gratchev \& Sassa [26] \\ Brown clay & Recon. & Ring shear & 12-60-120-300 & Negative & Healing, broken bonds restoration at a lower rate & \\ Kaolin clay & Recon. & Direct shear & 3.6-36-360 & Negative & Larger excess PWP with a higher rate & [PERSON] et al. [19] \\ Kaolin clay & Recon. & Ring shear & 0.09-0.6-1-11.1 & Positive & & & \\ Kaolin clay & Recon. & -74\% & Ring shear & 0.002-0.6-1-120 & Positive & & \\ landslide & Recon. & -74\% & Ring shear & 0.002-0.6-1-120 & Positive & & \\ Kaolin clay & Recon. & -74\% & Ring shear & 0.02-0.1-0.2-1-10 & Positive & & \\ Kaolin clay & Recon. & -74\% & -74\% & -74\% & -74\% & -74\% & -74\% \\ Kaolin clay & Recon. & -74\% & -74\% & -74\% & -74\% & -74\% & -74\% \\ Kaolin clay & Recon. & -74\% & -74\% & -74\% & -74\% & -74\% & -74\% \\ Kaolin clay & Recon. & -74\% & -74\% & -74\% & -74\% & -74\% & -74\% \\ Kaolin clay & Recon. & -74\% & -74\% & -74\% & -74\% & -74\% & -74\% \\ Kaolin + & Recon. & -74\% & -74\% & -74\% & -74\% & -74\% & -74\% \\ Bentonite clay & -74\% & -74\% & -74\% & -74\% & -74\% & -74\% & -74\% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Rate effect of 11 clay soils under ring shearing. Furthermore, it is worth mentioning that two types of stick-slip (SS) shear patterns were observed during the entire undrained shear process, i.e., random SS during pre-peak stage for both YACK and OACK samples, and intense SS during the post-peak stage for YACK samples. Figure 8a,b show the stress-strain curves of both YACK and OACK during the pre-peak stage in undrained shearing. The'saw-tooth' shape disturbance of the stress-strain curves was only present when the critical threshold strain rate associated with the confining stress was reached. For a low confining stress of 100 kPa, the critical rate was found to be as low as 0.01%/h, while for a higher confining stress of 600 kPa, the critical rate could be 0.1%/h. Additionally, the fluctuation of stresses was quite regular in OACK, whose bond structure was completely developed. The intensity of the fluctuation increased as the axial strain approached the peak. In contrast, in YACK, the fluctuations were more random, occurring both in the vertical (stress) axis and the horizontal (strain) axis. This randomness indicates the immature nature of the cementitious bonds in YACK; in other words, the bonds were simultaneously gaining strength due to curing and losing strength due to shearing, resulting in a coupling between the slow rate of shearing and the curing time effects. Figure 9a shows the stress-strain curve of YACK during the post-peak stage of undrained shearing. According to the theory of stick-slip, under the same shear rate and roughness of the shear plane, the stick-slip effect could be manifested by the normal force on the sliding shear plane, which could be quantified by the bandwidth of the saw-tooth- shaped shear stress curve. The results indicated bandwidth values of 3.1 kPa, 4.4 kPa, 7.9 kPa, and 9.2 kPa under confining stresses 100 kPa and 600 kPa, respectively. It  
Figure 8: Stick-slip shear pattern observed in the pre-peak shearing stage of both YACK and OACK: (**a**) shearing at a low confining stress of 100 kPa; (**b**) shearing at a high confining stress of 600 kPa.