## 3 Results
### Shear Strengths of Loess and Paleosol Samples and Their Strength Parameters  
In line with the Chinese National Standards (CNS) GB/T50123-2019 [37], the peak strength on the shear stress-shear displacement curve is defined as the shear strength. For curve without a peak value, the shear stress at the point where the shear displacement is equal to 20% of samples' height (e.g., 5 mm of shear displacement) is defined as the shear strength. Figure 4 exhibits their shear strength envelopes with different moisture contents. The shear strength decreases as the normal stress decreases and the initial moisture content increases. For loess samples, when the normal stress is 200 kPa, the increase in the initial water content clearly reduces the shear strength (199.2 kPa at 11% and 106.2 kPa at 33%,  
Figure 3: Curves of shear stress versus shear displacement for paleosol samples.  
respectively). This means water has a weakening effect on the shear strength of loess. When the initial moisture content rises from 11% to 21%, the shear strength at 200 kPa of normal stress decreases from 199.2 kPa to 134.6 kPa, with a reduction magnitude of 32.4%, whereas it is 21.1% when the initial moisture content increases from 21% to 33% (134.6 kPa and 106.2 kPa, respectively), indicating that the softening effect of water on shear strength is more pronounced at a low initial moisture content than at a high initial moisture content. The same variation trend is seen for paleosol samples, but those have a higher shear strength than loess. The reduction magnitudes of shear strength at the normal stress of 200 kPa are 38.2% and 31.8% when the initial moisture content is increased from 11% to 21% and from 21% to 33%, respectively. This suggests that the paleosol is more sensitive to water than loess.  
Their shear strength parameters are listed in Table 3. We can understand from these that \(c\) evidently decreases with an increased initial moisture content. When the initial moisture content increases from 11% to 33%, the \(c\) of loess and of paleosol is reduced by 89.7% and 88.4%, respectively. Compared with \(c\), \(\varphi\) shows a decreasing trend as a whole, but its reduction amplitude does not show large variation. This demonstrates that the weakening effect of water against shear strength is largely reflected in a reduction in \(c\). In conducting a comprehensive investigation of the relationship between \(c\) and the initial moisture content, we found, when fitting the data in Table 3, that \(c\) decreased exponentially with an increased initial moisture content (Figure 5). Similar results have also been published in the relevant literature [20].  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Strength** & \multicolumn{6}{c}{**Initial Moisture Content/\%**} \\  & **Parameter** & **11** & **13** & **17** & **21** & **26** & **33** \\ \hline \multirow{2}{*}{Loess} & \(c\) (kPa) & 88.2 & 69.6 & 47.7 & 34.7 & 24.3 & 9.1 \\  & \(\varphi\) (\({}^{\circ}\)) & 26.4 & 26.5 & 26.2 & 26.5 & 26.3 & 26.1 \\ \multirow{2}{*}{Paleosol} & \(c\) (kPa) & 151.1 & 125.4 & 95.8 & 65.3 & 37.1 & 17.6 \\  & \(\varphi\) (\({}^{\circ}\)) & 29.9 & 28.9 & 28.7 & 29.1 & 28.6 & 28.3 \\ \hline \hline \end{tabular} Note: \(c\) is cohesion; \(\varphi\) is internal friction angle.  
\end{table}
Table 3: Shear strength parameters of loess and paleosol.  
Figure 4: Shear strength envelopes of samples with different initial moisture contents.