## 3 Results and Discussion  
The FTIR spectra of epoxy resin, PAPI and prepolymer are shown in Figure 2a. The spectra showed that the characteristic groups of the polyurethane prepolymer were the stretching vibration peak of carbonyl at 1729 cm\({}^{-1}\), which confirmed that the epoxy resin reacted with isocyanate during the pre-polymerization, and the hydroxyl group of epoxy resin peak was at 3058 cm\({}^{-1}\). The characteristic absorption peak of PAPI(-NCO) was observed at 2240 cm\({}^{-1}\). Compared with NPEF-170, the absorption peak of prepolymer at 3058 cm\({}^{-1}\) became weaker and wider after the reaction between PAPI and epoxy resin; the infrared peak of prepolymer disappeared at 2240 cm\({}^{-1}\). Therefore, the synthesis of the modified epoxy resin was accomplished by the reaction between the isocyanate and the hydroxyl group. Figure 2b shows the FTIR spectra of EPUP-WG-1, EPU-WG-1 and PU-WG-1. The spectrum showed the C=O of the isocyanate trimer peak at 1710 cm\({}^{-1}\), and \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & & & & & & & & & & & \\ \cline{2-10}
**Sample** & **HEP-330N** & **HSH-303** & **Glycerin** & **AK805** & **H\({}_{2}\)O** & **DMP-30** & **DBTDL** & **WG** & **KH560** & **NPEF-170** & **PAPI** \\  & **(g)** & **(g)** & **(g)** & **(g)** & **(g)** & **(g)** & **(g)** & **(g)** & **(g)** & **(g)** & **(g)** \\ \hline PU-WG-1 & 8.4 & 13.1 & 10 & 1.5 & 1.7 & 0.3 & 0.1 & 0 & 1.5 & 0 & 64.9 \\ PU-WG-2 & 8.4 & 13.1 & 10 & 15 & 1.7 & 0.3 & 0.1 & 5 & 1.5 & 0 & 64.9 \\ PU-WG-3 & 8.4 & 13.1 & 10 & 1.5 & 1.7 & 0.3 & 0.1 & 10 & 1.5 & 0 & 64.9 \\ PU-WG-4 & 8.4 & 13.1 & 10 & 1.5 & 1.7 & 0.3 & 0.1 & 15 & 1.5 & 0 & 64.9 \\ PU-WG-5 & 8.4 & 13.1 & 10 & 1.5 & 1.7 & 0.3 & 0.1 & 20 & 1.5 & 0 & 64.9 \\ EU-WG-1 & 8.4 & 13.1 & 10 & 1.5 & 1.7 & 0.3 & 0.1 & 0 & 1.5 & 28 & 64.9 \\ EU-WG-2 & 8.4 & 13.1 & 10 & 1.5 & 1.7 & 0.3 & 0.1 & 5 & 1.5 & 28 & 64.9 \\ EU-WG-3 & 8.4 & 13.1 & 10 & 1.5 & 1.7 & 0.3 & 0.1 & 10 & 1.5 & 28 & 64.9 \\ EU-WG-4 & 8.4 & 13.1 & 10 & 1.5 & 1.7 & 0.3 & 0.1 & 15 & 1.5 & 28 & 64.9 \\ EU-WG-5 & 8.4 & 10 & 10 & 1.5 & 1.7 & 0.3 & 0.1 & 20 & 1.5 & 28 & 64.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Formulas of different grouting materials. the characteristic peak of oxazolidone (OX) ring was observed at 1763 cm\({}^{-1}\). For PU-WG-1, the characteristic peak of the oxazolidone ring disappeared [17]. The industry standard, AQ/T1090-2020 stipulated that the maximum reaction temperature (MRT) should be less than 95 \({}^{\circ}\)C. The reaction temperature was measured by a temperature sensor inserted into the center of the sample, and the reaction temperature reached the maximum in the 50 th second for the PU-WG system (Figure 3a). For PU-WG-1, the MRT reached 124.6 \({}^{\circ}\)C, which was the highest among the PU-WG systems. With the addition of WG, the MRT of all systems decreased (Figure 3b), which indicated that WG reduced the MRT of the PU dramatically. One possible reason is that the generated CO\({}_{2}\) reacted with WG to form orthosilicic acid, and then much heat was absorbed when a dehydration reaction took place [14]. As Figure 3b shows, the MRT of the EPU-WG system was 148 \({}^{\circ}\)C, which was higher than the PU-WG system. This is because the addition of epoxy resin increased the content of the hydroxyl group (-OH), which could react with free isocyanate (-NCO) in the system [18]. However, due to the heat generated by the reaction of -OH in epoxy resin and -NCO was partly released in the process of the prepolymer, the MRT of EPUP-WG-1 was lower than that of EPU-WG-1. It is worth noting that the MRT of the three systems decreased significantly after 5 phr of WG was added; additionally, when the content of WG was 15 phr, the MRT of EPUP-WG system decreased further to 89 \({}^{\circ}\)C.  
The industry standard, AQ/T1090-2020 stipulated that the compressive strength should be more than 0.01 MPa.