## 3 Results and Discussion  
### Parameter Screening with Plackett-Burman (PBD) and RSM Modeling  
The global perturbation analysis method examined parameter influences from external and internal sources. Therefore, a screening strategy was used to choose the most sensitive embankment stability coefficient values, followed by an assessment of their total sensitivity. The initial screening of the 14 factors affecting railway embankment stability used PBD by Minitab 19.0 [17]. These factors include cohesion (\(c\)), elastic modulus (\(E\)), water level rate of change (\(v\)), internal friction angle (\(\phi\)), train static load (\(L\)), infiltration coefficient (\(k_{s}\)), soil unit weight (\(\rho_{s}\)), elevation of fluctuating water level (\(H\)), [PERSON]'s ratio (\(v\)), residual moisture content (\(\theta_{r}\)), and van Genuchten fitting parameters (\(n\), \(m\), and \(\alpha\)). [PERSON] [17] found that \(\theta_{s}\), \(n\), \(m\), \(\alpha\), and \(\theta_{r}\) have little effect on earth material embankment stability and were assumed to be negligible. This study only examined \(L\), \(v\), \(\rho_{s}\), \(c\), \(k_{s}\), \(\phi\), \(E\), \(H\), and \(v\). Each variable was tested at two independent levels, with the lower level (\(-1\)) set to drop by 10% from the baseline basic working norm and the higher level (\(+1\)) set to grow by 10% [17]. Table 1 shows a 20% difference between the higher and lower levels. A probability value (\(p\)-value) below 0.05 in the statistical analysis showed a significant influence on the railway embankment stability factor, guiding the PBD test factor selection, as shown in Table 2. These parameters' primary effects were assessed using PBD and were further evaluated for main effects using BBD-RSM. The normalized effects show that when rising lake water levels impact the railway slope, the impact of each influencing parameter is ranked in ascending order: \(\mu<E<v<Ks<H<L<<\rho_{s}<\phi\). Interestingly, \(c\), \(\rho_{s}\), and \(\phi\) greatly impact the global static stability and safety factor of the railway embankment slope. \(E\), \(v\), \(Ks\), \(H\), and \(L\) are less important. PBD results show that when water levels drop, the sensitivity of each parameter is classified as follows: \(E<\mu<v<K_{s}<L<\rho_{s}<H<c<\phi\). This indicates that \(\phi\), \(c\), \(H\), and \(\rho_{s}\) greatly affect the railway slope's global static stability and safety factor. The parameters \(E\), \(v\), \(K_{s}\), \(L\), and \(\mu\) have minimal impact on the global static stability of the railway slope and its factor of safety. A preliminary analysis shows that the mechanical properties (\(\phi\), \(c\), and \(\rho_{s}\)) of the railway slope are affected through its global stability and safety factor during varying water levels. Train static loading does not affect the global static slope factor of safety, but it is stronger when water levels rise than decline. The soil coefficient of permeability, \(K_{s}\), is less sensitive to the railway slope's global static stability safety coefficient, possibly due to embankment compaction rates [17]. In addition, the seepage flux (\(K_{s}\), \(H\), and \(v\)) sensitiveness on the railway slope's static stability coefficient is greater with falling water levels than with rising levels. The lake's fast water level variations may explain this (assuming instantaneous pore water pressure response). Thus, the railway embankment slope seepage field characteristics (\(K_{s}\), \(H\), and \(v\)) will need to be monitored for long-term sensitivity. Based on the standardized effects chart, three of the most influential components for the increasing water level scenario and four for the dropping water level scenario were selected for BBD-RSM analysis. The variables \(H\), \(\rho_{s}\), \(c\), and \(\phi\) were found to be critical through a Plackett-Burman design test. We examined stability factors by analyzing response variables for rising (\(\rho_{s}\), \(c\), and \(\phi\)) and dropping (\(\rho_{s}\), \(c\), \(H\), and \(\phi\)) water levels.