## 3 Results
### Effects of Fiber Length and Content on Soil Properties Under Two Soil Conditions
#### 3.1.2 Crack Resistance  
As shown in Figure 2, the crack ratio of both soil types initially decreased and then increased after the incorporation of coir fiber, which aligns with the observed soil crack images (see Appendix A). The effects of different fiber lengths and contents on crack resistance varied. At a 0.2% fiber content, the 5 cm fiber length exhibited the best crack resistance. When the content increased to 0.4%, the 3-4 cm fiber length showed optimal performance. At a 0.6% content, the 1 cm fiber length was the most effective in mitigating cracking. Further analysis indicated that the optimal fiber content varied with fiber length: for 1-2 cm fibers, 0.6% content provided the best crack resistance; for 3-4 cm fibers, 0.4% content was the most effective; while for 5 cm fibers, the optimal content was 0.2%. To further investigate the effects of coir fiber on soil properties in different soil types, a correlation analysis was conducted (Figure 3). The results indicate that an increase in fiber content enhances the porosity and shear strength without compromising reinforcement effectiveness. Instead, fiber incorporation improves the bonding between soil particles, contributing to strength enhancement. Longer fibers and a higher fiber content result in greater \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Fiber** & **Fiber** & **Total Porosity** & **Aeration Porosity** & **Capillary** & **Bulk Density** & **Hydraulic** \\
**Content** & **Length** & **(\%)** & **(\%)** & **Porosity** & **(g/cm\({}^{3}\))** & **Conductivity** \\ \hline CK & & 44.4 \(\pm\) 0.45 c & 5.13 \(\pm\) 0.05 d & 39.27 \(\pm\) 0.41 a & 1.3137 \(\pm\) 0.00769 a & 0.6 \(\pm\) 0.01 b \\  & 1 cm & 46.27 \(\pm\) 0.55 bc & 10.87 \(\pm\) 0.06 c & 35.39 \(\pm\) 0.62 b & 1.1687 \(\pm\) 0.01943 b & 0.65 \(\pm\) 0.01 a \\  & 2 cm & 46.5 \(\pm\) 0.74 bc & 11.16 \(\pm\) 0.12 bc & 35.34 \(\pm\) 0.82 b & 1.1907 \(\pm\) 0.0111 b & 0.65 \(\pm\) 0.01 a \\
0.2\% & 3 cm & 47.67 \(\pm\) 0.61 b & 11.72 \(\pm\) 0.07 ab & 35.95 \(\pm\) 0.54 b & 1.052 \(\pm\) 0.03424 c & 0.67 \(\pm\) 0.01 a \\  & 4 cm & 49.83 \(\pm\) 0.47 ab & 11.51 \(\pm\) 0.11 b & 38.33 \(\pm\) 0.37 ab & 1.1939 \(\pm\) 0.02043 b & 0.67 \(\pm\) 0.01 a \\  & 5 cm & 48.87 \(\pm\) 0.26 ab & 11.87 \(\pm\) 0.19 ab & 36.99 \(\pm\) 0.44 b & 1.0637 \(\pm\) 0.01517 c & 0.67 \(\pm\) 0.02 a \\  & 1 cm & 46.4 \(\pm\) 0.27 bc & 11.11 \(\pm\) 0.08 bc & 35.29 \(\pm\) 0.65 b & 1.1267 \(\pm\) 0.01559 b & 0.66 \(\pm\) 0.02 a \\  & 2 cm & 47.3 \(\pm\) 0.38 b & 11.31 \(\pm\) 0.09 b & 35.99 \(\pm\) 0.29 b & 1.1503 \(\pm\) 0.02305 b & 0.66 \(\pm\) 0.01 a \\
0.4\% & 3 cm & 48.93 \(\pm\) 0.7 ab & 12.01 \(\pm\) 0.21 a & 36.93 \(\pm\) 0.8 ab & 1.1483 \(\pm\) 0.0645 b & 0.67 \(\pm\) 0.01 a \\  & 4 cm & 50.7 \(\pm\) 0.59 a & 12.06 \(\pm\) 0.30 b & 38.64 \(\pm\) 0.62 b & 1.0857 \(\pm\) 0.0242 c & 0.67 \(\pm\) 0.02 a \\  & 5 cm & 47.9 \(\pm\) 0.15 b & 11.73 \(\pm\) 0.09 ab & 36.17 \(\pm\) 0.16 b & 1.112 \(\pm\) 0.03291 b & 0.68 \(\pm\) 0.01 a \\  & 1 cm & 46.83 \(\pm\) 1.17 bc & 11.42 \(\pm\) 0.07 b & 35.41 \(\pm\) 11.1 b & 1.101 \(\pm\) 0.04219 b & 0.65 \(\pm\) 0.02 a \\  & 2 cm & 47.67 \(\pm\) 0.61 b & 11.72 \(\pm\) 0.07 ab & 35.95 \(\pm\) 0.54 b & 1.052 \(\pm\) 0.03424 c & 0.67 \(\pm\) 0.01 a \\
0.6\% & 3 cm & 48.57 \(\pm\) 0.37 ab & 12.14 \(\pm\) 0.14 a & 36.43 \(\pm\) 0.27 b & 1.101 \(\pm\) 0.02680 b & 0.68 \(\pm\) 0.01 a \\  & 4 cm & 50.37 \(\pm\) 0.47 ab & 11.99 \(\pm\) 0.09 a & 38.37 \(\pm\) 0.41 ab & 1.0773 \(\pm\) 0.02422 c & 0.68 \(\pm\) 0.01 a \\  & 5 cm & 46.27 \(\pm\) 0.48 bc & 11.71 \(\pm\) 0.08 ab & 34.56 \(\pm\) 0.41 b & 1.0467 \(\pm\) 0.0227 c & 0.69 \(\pm\) 0.02 a \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Physical properties of Soil-type B.  
improvements in the shear strength and reinforcement coefficient, particularly under high confining pressure, leading to increased soil stability. The peak deviatoric stress index showed a significant positive correlation with the reinforcement coefficient, further confirming the dual reinforcing effect of fibers.