## 3 Results and Discussion
### Unconfined Compressive Strength (UCS) Results  
Figure 9 shows the effects of different SA ratios and SA + MICP combinations on the UCS of the S1, S2, and S3 soil specimens treated using the injection method. In general, an increasing trend in UCS values was observed with a higher SA content, and in some cases, the addition of MICP further enhanced the strength. However, this effect varied depending on the soil type. Moreover, for the S1 soil, specimens treated with 0% and 0.5% SA could not retain their shape after treatment and therefore were not subjected to UCS testing. In the  
Figure 8: Hydraulic conductivity results of soil specimens improved by the mixing method. specimens prepared with only SA, an increase in UCS was observed with an increasing SA content, regardless of the soil particle size. The UCS values obtained for the S1, S2, and S3 soils reached maximum values of 43 kPa, 121 kPa, and 52 kPa, respectively. In the injection applications where SA and MICP were used together, a general increase in strength was observed in the soil specimens. However, in the fine-grained S1 soil, the desired structure could not be formed; the specimens disintegrated after injection and could not be brought to the testing stage. A general increasing trend in strength was observed with higher SA content, but this effect was limited in the coarse-grained S3 soil. This may be attributed to the insufficient accumulation of binding material between the larger particles. Figure 10 presents the effects of different SA ratios and 5%, 10%, and 15% pellet contents on UCS of S1, S2, and S3 soil specimens improved using the mixing method, under  
Figure 9: UCS results of soil specimens improved by the injection method. both SA and SA + MICP applications. In general, SA + MICP combinations produced significantly higher strength values compared to SA alone, especially at higher pellet contents. This indicates that biological cementation is effective in enhancing mechanical strength. While only SA resulted in limited strength improvement, the addition of MICP contributed to the formation of stronger and more durable structures. As a result of SA-based stabilization processes applied using the mixing method, a clear increasing trend in UCS values was observed with higher SA and pellet contents. The maximum UCS values obtained for the S1, S2, and S3 soil types were 398 kPa, 247 kPa, and 91 kPa, respectively. For all soil types, the highest strength values were obtained in specimens treated with 2.5% SA and 15% pellet contents, indicating that this additive combination provided the most effective stabilization conditions in terms of mechanical performance. An increasing trend in soil strength was observed with higher SA and MICP ratios in the S1, S2, and S3 soils. These results indicate that the additives had the most pronounced effect in the S1 soil, while also providing a significant improvement in the S2 soil. In all soil types, the highest strength values were obtained with the combination of 2.5% SA and 15% pellet content, demonstrating that this was the most effective additive configuration in terms of mechanical performance. In terms of UCS, both methods exhibit potential for enhancing the mechanical properties of soils; however, the mixing method has demonstrated higher strength values, particularly at elevated additive ratios. In SA + MICP combinations applied via the injection method, although low hydraulic conductivity performance improved due to the controlled delivery of additives into the soil, UCS values remained limited. This outcome is attributed to the non-uniform distribution of additives and the insufficient duration of microbial activity [39]. Conversely, the mixing method allows for the better integration of additives with the soil matrix, leading to significant increases in UCS values, especially in SA + MICP combinations containing 2.5% SA and 15% pellet. For instance, UCS values as high as 398 kPa were achieved in the S1 soil series.