## 3 Analysis and Discussion of Test Results  
### Analysis of Internal Friction Angle and Cohesive Force Results  
Table 6 demonstrates that the internal friction angle and cohesion of consolidated soil are significantly influenced by different geopolymer content and curing age. The utilization of geopolymers for stabilizing loess can enhance its shear strength, particularly cohesion. At the age of 28 days, the lower solidified soil mixed with 20% geopolymer exhibits a maximum cohesion of 81.09 kPa, representing a 75.32% increase compared to plain soil. The lower solidified soil mixed with 25% geopolymer demonstrates a maximum internal friction angle of 31.20\({}^{\circ}\), which is 64.04% higher than that of plain soil.  
Figure 7 illustrates the trend of the internal friction angle and cohesion of the stabilized soil with the inclusion of polymer. The graph demonstrates that as the amount of polymer added increases, the internal friction angle initially rises and subsequently stabilizes. Similarly, the cohesive force exhibits an initial increase followed by a decrease. The addition of steel slag fine powder with rich edges and corners in the solidified soil enhances the interaction force between soil particles. As the steel slag content increases, the contact area between steel slag and loess also increases, leading to an increase in the internal friction angle of solidified loess. Additionally, the combination of steel slag and fly ash, activated by alkaline water glass, produces C-S-H and C-A-S-H gels that fill the gaps between soil particles and strengthen the connections between them, thereby improving the soil's cohesion. However, when the addition of geopolymer exceeds a certain threshold, it leads to a decrease in the proportion of net loess content. This results in a reduction in loess skeleton and the aggregation of cementitious materials, forming a lump. However, this is insufficient to effectively fill the voids between soil particles; it merely adheres to the surface of the soil mass. Consequently, while the internal friction angle remains stable, the cohesion decreases. When the local polymer content remains constant, the internal friction angle and cohesion increase with longer curing time. For instance, with a geopolymer content of 20%, the internal friction angle and cohesion at 28 days of curing time are 1.23 times and 1.48 times higher than at 7 days of curing time, respectively. Similarly, at 14 days of curing time, the internal friction angle and cohesion are 1.15 times and 1.36 times higher. When  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Curing Age** & **Addition Amount** & **0\%** & **5\%** & **10\%** & **15\%** & **20\%** & **25\%** \\ \hline \multirow{2}{*}{7 d} & Cohesion (kPa) & 38.05 & 40.55 & 42.14 & 50.09 & 54.86 & 46.9 \\  & Angle of internal friction (\({}^{\circ}\)) & 15.38 & 22.50 & 23.55 & 25.25 & 25.38 & 25.34 \\ \hline \multirow{2}{*}{14 d} & Cohesion (kPa) & 40.55 & 41.34 & 43.7 & 50.88 & 59.63 & 43.73 \\  & Angle of internal friction (\({}^{\circ}\)) & 18.42 & 23.46 & 25.3 & 27.19 & 27.11 & 28.27 \\ \hline \multirow{2}{*}{28 d} & Cohesion (kPa) & 46.11 & 59.62 & 65.99 & 75.53 & 81.09 & 69.96 \\  & Angle of internal friction (\({}^{\circ}\)) & 19.2 & 24.18 & 24.4 & 24.36 & 31.12 & 31.20 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Internal friction angle and cohesion of solidified soil under different polymer content and curing age.  
the geopolymer content is 5% and the curing time is 28 days, the internal friction angle and cohesion are 1.07 times and 1.47 times higher than at 7 days of curing time, and 1.03 times and 1.44 times higher than at 14 days of curing time. The results of the direct shear test indicate that both curing time and geopolymer content significantly influence cohesion, while the internal friction angle is primarily affected by the geopolymer content, with little impact from curing time.