# Experimental Investigation and Mechanism of Fly Ash/Slag-Based Geopolymer-Stabilized Soft Soil+
## 3 Response Surface Analysis
### Stability Study of Geopolymer Stabilized Soft Soil
#### 3.4.2 Wet-Dry Cycle Tests on Geopolymer-Stabilized Soft Soils  
Figure 7 shows the change in the appearance of the geopolymer-stabilized silty soft soil with a geopolymer content of 10% under different numbers of wet-dry cycles. For the specimen with a 10% geopolymer content, there was obvious peeling of the outer skin on the surface of the specimen after one wet-dry cycle, serious damage after two to four cycles, and almost all of the outer layer of the specimen peeled off after the fourth cycle. The specimen exhibited local collapse and cracks at the end of the sixth cycle. The specimens with a 15% geopolymer content started to develop minor cracks and small pieces peeled off after the fourth wet-dry cycle. In contrast, for the specimens with geopolymer contents of 20% and 25%, the surfaces were almost completely intact after six wet-dry cycles. The above phenomenon demonstrates that a proper increase in the geopolymer content of stabilized soil will provide better resistance to damage caused by wet-dry cycles.  
Figure 6: UCS of unsoaked and soaked geopolymer-stabilized soil.  
The variations in the strengths of the stabilized soils with different geopolymer contents with an increasing number of wet-dry cycles are shown in Figures 8 and 9. The bottom horizontal axis of the graph is the number of wet-dry cycles, and the top horizontal axis is the time of standard maintenance of the stabilized soil corresponding to the number of cycles. The strengths of the standard stabilized specimens exhibit an overall increase with increasing age, but the lower the geopolymer content of the stabilized soil is, the smaller the increase is. Under the wet-dry cycles conditions, the specimens with different geopolymer contents exhibited a trend of gradually decreasing strength with an increasing number of wet-dry cycles, and the strengths of the specimens under the wet-dry cycles were lower than their corresponding standard curing strengths. This is because in the process of the wet-dry cycles, the internal structure of the specimens is damaged due to the dry shrinkage and wet expansion processes, especially the formation of cracks at the bonding weakness points between the soil particles [19]. As the number of cycles increased, the specimens continued to shrink and expand in the dry and wet phases of the cycles, respectively, which led to larger cracks forming until damage occurred. The strength of the sample containing 20% ground polymer at the end of eight cycles was 982.16 kPa, that is, a strength loss of 51% compared to that under zero cycles. However, the strength of the specimen with continued standard curing was 2439.84 kPa, which was much higher than that of the dry-wet cycle specimens. As the geopolymer content increased, the strength of the specimens after eight cycles increased, and the strength losses of the stabilized soil with 10%, 15%, 20%, and 25% geopolymer contents were 100%, 67%, 51%, and 42%, respectively. This also indicates that increasing the geopolymer content can effectively reduce the strength loss and enhance the performance of the stabilized soft soil against wet-dry cycles.  
Figure 8: Variations in the compressive strengths of the samples with curing agent contents of 10% and 15% with an increasing number of wet–dry cycles.  
Figure 7: Appearance changes of specimens with 10% geopolymer content in wet–dry cycles. The number of cycles is 2, 4, 6, 8.