## 2 Simulation Methods  
### Molecular Model of Epoxy Resins  
DGEBA, DGEDDS, and AEOR were utilized as material models to investigate mechanism of sand cured by epoxy resin. DGEBA is a kind of polymer containing bisphenol A and epoxy group functional groups, forming a three-dimensional network structure with high properties through the reaction between them. DGEDDS with bisphenol S and epoxy group functional groups was also selected in the study. In addition, EOR was also selected as the third polymer to validate that the inclusion of oxygen atoms can improve the adsorption capacity. Among the three types of epoxy resin, DGEBA and the DGEDDS belong to glycerol ether epoxy resin; however, AEOR belongs to linear aliphatic epoxy compounds. The epoxy group is the characteristic group of epoxy resin, and its content is an important indicator to evaluate the nature of a substance. There are two main parameters to describe the content of the epoxy group, the namely epoxy equivalent and epoxy value. The epoxy equivalent refers to the quality of 1 mol of epoxy resin; the epoxy value refers to the amount of epoxy substance contained in 100g of resin. The latter is often used for the measurement of curing agents and the expression of the amount, and the epoxy value was adopted in this study. To ensure that each resin had a similar molecular weight, the simulation was controlled to have about 50 carbon atoms [33]. In the practical application process, it is also necessary to control the ratio relationship between the soil and curing agent to calculate the dosage, and the specific parameters are shown in Table 1.  
Among the epoxy resins, DGEBA is known as the universal epoxy resin, and its yield is the largest, because its raw material is easy to obtain and its cost is the lowest. In this study, the polymerization degree n of DGEBA was set to be 2. The structural formula and the corresponding molecular model are shown in Figures 1a and 1b, respectively.  
DGEDDS has excellent heat resistance due to it containing sulfur. In this study, the polymerization degree n of DGEDDS was set to be 2, and its structural formula is shown in Figure 2a. Due to the molecular structural formula containing two hydroxyl groups and one sulfone group, DGEBA is more acidic compared to both DGEBA and AEOR. The structural formula is shown in Figure 2b.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Types of Epoxy** & **Chemical** & **Molecular Weight** & **Epoxy Value** & **References** \\
**Resins** & **Formula** & **(g\(\cdot\)mol\({}^{-1}\))** & **(mol)** & **References** \\ \hline DGEBA & C\({}_{57}\)H\({}_{64}\)O\({}_{10}\) & 904 & 0.222 & [40] \\ DGEDDS & C\({}_{48}\)H\({}_{46}\)O\({}_{16}\)\({}_{5}\)\({}_{3}\) & 870 & 0.230 & [41] \\ AEOR & C\({}_{56}\)H\({}_{86}\)O\({}_{14}\) & 983 & 1.424 & [42] \\ \hline \hline \end{tabular}
\end{table}
Table 1: Parameters for three types of epoxy resins.  
Figure 1: Structural formula and molecular model of DGEBA. (**a**) Structural formula; (**b**) molecular model.  
AEGR is prepared by oxidizing the double bonds of aliphatic epoxy olefin [43]. Based on its structural formula, it can be observed that AEOR predominantly comprises carbon chains and possesses multiple epoxy groups within its molecular structure. In this study, the polymerization degree n of AEOR was set to be 7. The structural formula and the corresponding molecular model are shown in Figures 3a and 3b, respectively.  
Through Forcite in the software of Materials Studio (version 1.9.4), the molecular model of each compound was optimized to find the lowest energy state of the structure, so as to ensure the stable existence of each compound and cure the soil.