## 3 Test Result Analysis
### Dry-Wet Cycle Test
#### 3.2.1 Influence of Sand on The Dry-Wet Cycle Characteristics of Cemented Soil  
It is apparent from Figure 5 that the UCS of the CS-SS samples slightly increased first and then decreased with the increase of the number of dry-wet cycles under freshwater conditions, and decreased with the increase of the number of dry-wet cycles under seawater conditions, whereas the UCS of the control group samples increased with the increase of curing age. Moreover, the strength degradation of the CS-SS samples caused by the dry-wet cycle under seawater conditions was more remarkable than that under freshwater conditions. According to Equation (1), the average strength loss rate of the CS-SS samples after two dry-wet cycles could be obtained, as shown in Figure 6. Whether for freshwater or seawater dry-wet cycles, the average strength loss rate of the CS-SS samples after two dry-wet cycles increased with the increase of the sand particle size and decreased with the increase of sand particle content. When the sand particle size remained unchanged, the increase of sand particle content led to a denser distribution of sand particles in the cemented soil and more hydration products covering the surface of sand particles, forming a more compacted cementitious skeleton structure, which increases the ability to resist the structural destruction caused by the dry-wet cycle. When the sand particle content was kept unchanged, the sand particle size decreased, the specific surface area of sand particles increased, and the adhesion area of cement hydration products increased; this made the continuous bonding structure more compact, and the dry-wet cycle resistance of the sample increased. Therefore, the addition of fine sand can better improve the  
Figure 4: Failure modes of the CS-SS samples; (**a**) \(\alpha_{s}=0\%\), column split type; (**b**) \(\alpha_{s}=15\%\), core split type; (**c**) \(\alpha_{s}=30\%\), shear split type. resistance of the cemented soil to the dry-wet cycle erosion when the sand particle content remains unchanged. Figure 5: Relationship between dry–wet cycles and UCS of the CS-SS samples; (**a**) fine sand; (**b**) medium sand; (**c**) coarse sand. Figure 6: Relationship between UCS and sand particle content of CS-SS samples after two dry–wet cycles (the number is the average strength loss rate after the dry–wet cycle). 2.2 Physical Mechanism Explanation of the Influence of Sand on the Dry-Wet Cycle Characteristics of Cemented Soil  
To analyze the evolution of the microstructure and mineral composition of the CS-SS samples during the dry-wet cycle under seawater and freshwater conditions, the samples of the unconfined compression test corresponding to each round of dry-wet cycle were tested by SEM and XRD. The test results are shown in Figures 7-11. Figure 7 shows the SEM images of the CS-SS samples with the coarse sand in seawater under different dry-wet cycles. The microstructure of the samples before the dry-wet cycle test was compacted, as shown in Figure 7, and the hydration products of cement effectively cemented the soft soil particles to form an inlay-like cementitious structure with  
Figure 11: Ion chromatography test results of the CS-SS samples under seawater conditions; (**a**) seawater, \(N=1\) (medium sand, \(\alpha_{\rm s}=5\%\)), the peak area of Cl\({}^{-}\) is 0.47 \(\mu\)S-min; (**b**) seawater, \(N=2\) (medium sand, \(\alpha_{\rm s}=5\%\)), the peak area of Cl\({}^{-}\) is 0.95 \(\mu\)S-min; (**c**) seawater, \(N=2\) (medium sand, \(\alpha_{\rm s}=15\%\)), the peak area of Cl\({}^{-}\) is 0.82 \(\mu\)S-min. Figure 10: Mineral composition of the CS-SS samples (medium sand, \(\alpha_{\rm s}=15\%\)); (**a**) freshwater, different dry–wet cycles; (**b**) seawater, different dry–wet cycles; (**c**) \(N=2\), seawater and freshwater results. high strength.