## 5 Discussion  
It is an effective means to solve a disaster by crossing the unavoidable ground fissure at a large angle and selecting the appropriate composite foundation design. To verify the contribution of the composite foundation parameters to the optimization effect, the variance analysis of the numerical simulation results was carried out using the orthogonal test. Four factors, namely the elastic modulus A of the subgrade bed (only considering the bottom layer of the subgrade bed), the elastic modulus B of the embankment, the thickness C of the concrete baseplate, and the pile length D, were selected to analyze the impact on the dynamic response of the composite foundation in the ground fissure site, without considering the interaction between the factors. Each factor has four levels. The levels of influencing factor A are A1, A2, A3, and A4. Similar notation is adopted for B, C, and D. The table of influencing factor levels is shown in Table 6. In this paper, four factors and four levels of tests were used to optimize the parameters of the composite foundation. Orthogonal test table L16(45) was selected, and a column of error terms was added (Table 7). In the variance analysis, the significance level is taken as 0.10, 0.05, and 0.01 [45]. To explain the significance criterion, the influencing factor A is taken as an example. Let the F value of influencing factor A be \(F_{A}\); \(n_{1}\) and \(n_{2}\) are degrees of freedom for influencing factors and errors, respectively. The significance criteria for influencing factors are shown in Table 8. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Level** & **A/MPa** & **B/MPa** & **C/m** & **D/m** \\ \hline I & 80 & 40 & 0.6 & 10 \\ II & 100 & 60 & 1.0 & 15 \\ III & 120 & 80 & 1.4 & 20 \\ IV & 140 & 100 & 1.8 & 25 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Influencing factor level table. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Test Condition Number** & \multicolumn{4}{c}{**Test Factors and Levels**} \\ \cline{2-5}  & **A/MPa** & **B/MPa** & **C/m** & **D/m** & **E (Blank)** \\ \hline
1 & 80 & 40 & 0.6 & 10 & I \\
2 & 80 & 60 & 1.0 & 15 & II \\
3 & 80 & 80 & 1.4 & 20 & III \\
4 & 80 & 100 & 1.8 & 25 & IV \\
5 & 100 & 40 & 1.0 & 20 & IV \\
6 & 100 & 60 & 0.6 &  
the subgrade. The risk of ground fissure disaster can be controlled by increasing the pile length. The dynamic response of the foundation in the ground fissure site under train vibration load is very complicated. The dynamic response behavior of the Da'xi high-speed railway crossing the ground fissure zone in the Taiyuan Basin was studied using numerical simulation and orthogonal tests in this paper. The design parameters of the composite foundation in the ground fissure site were optimized. The research results provide new ideas and methods for studying the engineering stability of high-speed railways crossing the ground fissure zone worldwide. However, there are still some problems worth exploring, as follows:  
The interaction mechanisms between different types of ground fissures and train vibration load are different. It is unclear what protective measures should be taken for each type of ground fissure. Therefore, based on this study, the relationship between ground fissure types and train vibration loads can be further discussed, and reasonable prevention suggestions and measures for each type of ground fissure can be provided. Q.X. : methodology, validation, and writing--review editing. Q.H. : conceptualization and funding acquisition. C.M. : validation. L.G. : validation. G.H. : methodology. All authors have read and agreed to the published version of the manuscript. This work was supported by the National Natural Science Foundation of China (No. 41772274) and the National Key R&D Program of China (No. 2023 YFC3008404). Not applicable. The raw data supporting the conclusions of this article will be made available by the authors on request. Author [PERSON] was employed by the company China Highway Engineering Consultants Corporation.