## 2 Materials and Methods  
### Materials and Specim Preparation  
The granite residual soils studied in this research were sampled from a foundation pit in Shenzhen city, Guangdong province, China. With a warm and humid climate, Shenzhen is a typical area of distribution of granite residual soils. To obtain undisturbed samples of high quality, a hand-carved block sampling method [52] was adopted. First, block samples with dimensions of about 30 \(\times\) 30 \(\times\) 30 cm\({}^{3}\) were obtained using spades and knives. After that, soil samples were sealed immediately with plastic wrap and placed in wooden boxes padded with foam. Finally, the samples were transported to the storage room with a constant temperature of 20 \({}^{\circ}\)C and relative humidity of 98%. The fundamental physical properties of the granite residual soil were determined in a laboratory and are shown in Table 1. The natural water content, liquid limit, and plastic limit of the soil were 26.7%, 58.9%, and 27.3%, respectively. The mineral composition of the soil was obtained by X-ray diffraction analysis and the result is presented in Table 2. It can be seen that the soil studied mainly consisted of quartz and kaolinite. The grain size distribution curve of the soil was determined according to ASTM standard D422-63, 2007 [53]. As shown in Figure 2, the proportion of soil particles with grain size larger than 1 mm reached 32.4%, while the proportion of soil particles with grain size smaller than 0.075 mm was 48.7%. Soil particles with intermediate grain size are relatively few. This is consistent with the typical grading characteristics of granite residual soils [30]. Based on the position of the soil in the well-known Casagrande plasticity chart, as shown in Figure 3, the granite residual soil used in this study can be classified as clay with high plasticity.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \begin{tabular}{c} **Density** \\ \(\rho\) **(g/cm\({}^{3}\))** \\ \end{tabular} & \begin{tabular}{c} **Water Content** \\ \end{tabular} & \begin{tabular}{c} **Void Ratio \(e\)** \\ \end{tabular} & \begin{tabular}{c} **Specific** \\ **Gravity \(G_{s}\)** \\ \end{tabular} & \
\begin{tabular}{c} **Hydroatic** \\ **Conductivity K (cm/s)** \\ \end{tabular} &
\begin{tabular}{c} **Afterberg Limits (\%)** \\ \end{tabular} \\ \hline \(1.98\) & 26.7 & 0.74 & 2.72 & \(1.79\times 10^{-4}\) & 58.9 & 27.3 & 31.6 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Physical parameters of the granite residual soil.  
Before testing, triaxial specimens of 50 mm in diameter and 100 mm in height were carefully trimmed from the block samples. The procedures of specimen preparation are as follows: first, in order to minimize the disturbance caused by trimming, a wire cutting machine was used to cut the original block sample into 18 blocks of smaller size. During this stage, the plastic wrap was kept confined to the block samples so they would not break into pieces; secondly, the smaller blocks were trimmed by hand with a knife and saw, to obtain nearly cylindrical specimens. Finally, with the help of a split cylinder mold, cylindrical specimens with required dimensions were obtained.