## 3 Changes in Compressive Strength of Specimens before and after Freeze-Thaw  
After on-site drilling and sampling, the specimens were transported back to the laboratory for cutting and grinding. The size of the specimens finally obtained was \(\varphi\) 50 mm \(\times\) 100 mm. The specimens met the relevant requirements in the Engineering Rock Mass Test Method Standard [15] in terms of size and accuracy. In the freeze-thaw test, a state of being saturated with water after vacuuming was used. One freeze-thaw cycle lasted 12 h, including 6 h low-temperature freezing and 6 h thawing. All samples underwent 50 freeze-thaw cycles. In this paper, the specimens that underwent 0, 10, and 50 freeze-thaw cycles and the corresponding uniaxial compressive strength values were selected and compared, as shown in Figures 1 and 2 below.  
The uniaxial compression tests were conducted on the specimens under different freeze-thaw conditions. The test results are shown in Table 1 below.  
After 50 freeze-thaw cycles, the specimens became fragmented and the strength decreased by a relatively large amount, for the following reasons: (1) when the temperature is below 0 \({}^{\circ}\)C, the water freezes, the volume increases by about 9%, the cracks extend and deepen, then the specimens are broken after multiple freeze-thaw cycles; (2) the expansion coefficients of various minerals in the specimens are different, then the uneven expansion and contraction due to the temperature change cause the specimens to rupture.  
When the freeze-thaw test was completed, the measured uniaxial compressive strength value decreased from the initial 38.92 GPa (\(N=0\)) to 0.73 GPa (\(N=50\)), a decrease of 97%. At the same time, the value of the elastic modulus was also reduced by 98%. Therefore, the overall bearing capacity and the safety factor of the slope were reduced, then the risk of shallow collapse was increased, which was consistent with the conclusions of the safety factor shown in Figures 3-6.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Number of Freeze-Thaw Cycles** & **Compression Modulus E** & **Maximum Force** & **Compression Strength** \\ **(N)** & **(GPa)** & **(KN)** & **(GPa)** \\ \hline \(N=0\) & 2.51 & 68.68 & 38.92 \\ \(N=10\) & 1.89 & 39.43 & 20.91 \\ \(N=20\) & 1.43 & 22.83 & 11.63 \\ \(N=30\) & 0.28 & 10.5 & 5.35 \\ \(N=40\) & 0.24 & 9.86 & 4.69 \\ \(N=50\) & 0.03 & 1.36 & 0.73 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Strength values of specimens after different freeze-thaw cycles.  
Figure 1: Apparent morphology of specimens under different freeze-thaw cycles. (**a**) Before freeze-thaw cycles, the surface of the specimen was covered with tiny spidery cracks due to the high ice content. (**b**) After 10 freeze-thaw cycles, the pits and fine pores on the specimen surface gradually increased and deepened, the deterioration degree of the specimen was aggravated progressively. (**c**) The exfoliation of the specimen gradually increased after 50 freeze-thaw cycles, and finally the lower part of the specimen broke first. Moreover, the color of the specimen gradually deepened, changing from the initial brown–red–white to the brown–black peat color.