## 3 Results and Discussion
### Determination of Optimal PHW Dosage  
Additional LSDS tests were conducted for the sake of determining the optimal %PHW to be added, in which the %PHW of 1.0 was considered while preparing the loess-PHW mixture specimens at \(\omega\) equal to 14%, 18% and 22%, respectively. The results of the LSDS tests are summarised in Table 4. The \(\phi\)' value was the highest as the %PHW was 0.6. Higher \(\phi\)' value was found as well at the %PHW of 1.0. It is noted that the \(\phi\)' value for the specimens at \(\omega=14\%\) increased from 22\({}^{\circ}\) to 29.3\({}^{\circ}\) as the %PHW increased from 0.45 to 0.6. Then the \(\phi\)' value decreased to 20.3\({}^{\circ}\) as the %PHW further increased to 0.75. The \(\phi\)' value, however, increased to 25.1\({}^{\circ}\) as the %PHW was ultimately increased to 1.0. Similar tendency could also be observed for the specimens at \(\omega=18\%\) and 22%, respectively. It is evident that the optimal PHW dosage derived from this study was within a range of 0.55-0.65 considering specimen homogenisation and testing reliability. The main cause to as well lead to the increase in the \(\phi\)' value at the %PHW \(>\) 0.8 was investigated by means of a simple test where the height of PHW (h\({}_{\text{PHW}}\)) in the shear box was measured under different normal pressures, hence allowing a back-analysis of the height of loess (h\({}_{\text{loess}}\)) in the shear box. Figure 11 shows the variation of h\({}_{\text{loess}}\), \(\gamma_{\text{d}}\) and \(\phi\)' as the function of %PHWs added (i.e., 0.45, 0.6, 0.75 and 1.0) for the loess-PHW mixture specimens prepared at \(\omega=14\%\), 18% and 22%, respectively. The \(\gamma_{\text{d}}\) values of loess were very close to their maximum of 15.6 kN/m\({}^{3}\) from the Proctor curve (not shown) at %PHW of 0.8-1.0. This phenomenon was most likely ascribed to the densified loess resulting from a high %PHW added. It seemed that the shearing behaviour was governed by the amount of added PHW at %PHW \(<\)0.8 and that it, in turn, was governed by the densification effect as the %PHW was \(>\)0.8. To sum it up, the densification effect led to higher \(\phi\)' value at %PHW of 0.8-1.0, and this study identified the optimal PHW dosage to be 0.55-0.65 taking into account specimen homogenisation and testing reliability. The impact of the amount of water added would be discussed later in this paper.  
Figure 10: Comparison of relative horizontal displacement (RHD) at failure between SSDS and LSDS for three different water contents.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**LSDS**} \\ \cline{2-3}
**Specimen no.** & \(\Phi^{\prime}\) & \(\Phi^{\prime}\) & \(\mathbf{R^{2}}\) & \(\mathbf{Yd}\) \\  & **(\(\mathbf{c}^{\prime}\))** & **(\(\mathbf{kN/m^{3}}\))** \\ \hline LS14-0 & 31.0 & 0.965 & 13.72 \\ \hline LS14-0.45 & 22.0 & 0.942 & 14.07 \\ \hline LS14-0.6 & 29.3 & 0.999 & 14.20 \\ \hline LS14-0.75 & 20.3 & 0.961 & 14.32 \\ \hline LS14-1 & 25.1 & 0.995 & 14.53 \\ \hline LS18-0 & 20.1 & 0.977 & 13.72 \\ \hline LS18-0.45 & 22.4 & 0.906 & 14.09 \\ \hline LS18-0.6 & 28.1 & 0.966 & 14.21 \\ \hline LS18-0.75 & 22.2 & 0.976 & 14.35 \\ \hline LS18-1 & 27.1 & 0.995 & 14.56 \\ \hline LS22-0 & 22.7 & 0.987 & 13.72 \\ \hline LS22-0.45 & 16.3 & 0.930 & 14.10 \\ \hline LS22-0.6 & 22.2 & 0.999 & 14.23 \\ \hline LS22-0.75 & 15.3 & 0.990 & 14.37 \\ \hline LS22-1 & 17.8 & 0.807 & 14.59 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Effect of PHW dosage on the improvement of friction angle \(\phi^{\prime}\) measured in LSDS tests.  
Figure 11: _Cont._