## 3 Results and Discussion
### Microscopic Pore Characteristics  
Nuclear magnetic resonance (NMR) tests were conducted on the grouting reinforcement body subjected to varying numbers of freeze-thaw cycles. The test results indicated that the \(T_{2}\) spectrum curves of grouting reinforcement bodies with different crack dip angles exhibited minimal differences after undergoing freeze-thaw cycles. This similarity can be attributed to the fact that aside from differences in crack dip angles and slurry stone volumes, the grouting reinforcement body is primarily composed of red sandstone, which experiences similar freeze-thaw deterioration. Furthermore, the slurry stone volume constitutes only a small portion of the overall grouting reinforcement body volume. As a result, the overall microscopic pore characteristics of the slurry stones with varying crack dip angles remain relatively consistent. Figure 15 presents the \(T_{2}\) map of the sample after freeze-thaw cycles with a crack dip angle of 30\({}^{\circ}\), where the upper axis represents the converted pore radius. This figure also reflects the pore evolution characteristics of the grouting reinforcement bodies for all four crack dip angles. As illustrated in Figure 15: (1) During the first 30 cycles of freeze-thaw, the NMR signal intensity of the grouting reinforcement body sample exhibited a progressive increase, indicating the continuous development of internal pores and a corresponding expansion in porosity; (2) the \(T_{2}\) spectra of the sample reveal three distinct peaks. The first peak, spanning \(T_{2}\) values from 0.01-5 ms, corresponds to pore sizes of 0.001-0.05 \(\upmu\)m, indicative  
Figure 14: Wave velocity and wave velocity loss rate. Figure 15: \(T_{2}\) spectra of grouting reinforcement body in the freeze–thaw process. of microporous structures. The second peak, predominantly spanning \(T_{2}\) values between 5-350 ms, corresponds to pore sizes of 0.05-3.5 \(\upmu\)m, primarily indicating mesoporous structures, with minor contributions from both micropores and macropores. The third peak, characterized by \(T_{2}\) values between 350-10,000 ms, corresponds to pore sizes ranging from 3.5-100 \(\upmu\)m, indicative of macroporous structures; (3) as the number of freeze-thaw cycles increases, the \(T_{2}\) spectra of the specimen exhibit a noticeable upward growth, with the intensity of the NMR signal's three peaks rising accordingly, reflecting an expansion in the peak area. Moreover, as the freeze-thaw cycles progress, the three peaks display a distinct rightward shift, characterized by three pore transition phenomena: the increase of micropores transitioning to mesopores, the increase in mesopores shifting toward macropores, and the continuous increase in macropores. These observations indicate the overall deterioration of the sample under repeated freeze-thaw action, with an increase in internal pores and expansion of pore sizes. To quantitatively elucidate the evolution of micropore characteristics in the grouting reinforcement body during freeze-thaw cycles, the sample with a 30\({}^{\circ}\) crack dip angle was taken as a representative case to calculate the \(T_{2}\) spectra areas for micropores, mesopores, and macropores under varying freeze-thaw conditions. The corresponding results are presented in Table 4. The nuclear magnetic resonance (NMR) \(T_{2}\) spectra area is calculated by integrating the ordinates of all points along the \(T_{2}\) curve, and its magnitude is positively correlated with both the pore number and size in the sample. Consequently, the variation in the \(T_{2}\) spectra area directly reflects the evolution of pore characteristics within the sample.