## 3 Results and Discussion
### Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS) Analysis Results
The mixing method is considered to enable the more homogeneous distribution of SA and more effective calcite precipitation in fine-grained soils such as S1, due to the direct contact it provides between the additives and soil particles. However, despite this relatively positive effect, the desired performance level was not fully achieved. This  
Figure 14: (**a**) SEM, and (**b**) EDS results of the soil samples that improved by mixing method. Figure 13: (**a**) SEM, and (**b**) EDS results of the soil samples that improved by injection method. limitation is thought to result from the irregular adhesion of additives to particle surfaces during the mixing process, which in turn prevents SA from forming a continuous film layer within the microstructure. In the S2 series, SA and MICP additives were able to reach the particle surfaces through the mixing method and induced partial microstructural changes. Nevertheless, SEM images indicate that the binding film structures and calcite precipitations were mostly localized. This may be attributed to the viscoelastic nature of SA, which can lead to its uneven distribution within the pores, particularly in low-controlled mixing applications. In coarse-grained soils such as S3, the additives applied through the mixing method did not produce sufficient bonding effects at the microstructural level. The large and smooth particle surfaces hindered the adhesion of SA and the localized formation of microbial precipitates. As a result, calcite precipitations remained mostly confined to the surface, and the interparticle cementation effect was weak. EDS analysis indicates that the notable presence of carbon (10.28%) and calcium (7.41%) reflects partial CaCO\({}_{3}\) precipitation resulting from the application of SA and MICP additives via the mixing method. The high levels of oxygen and silicon on the surface, along with limited chloride (CI) content, suggest that the effect of the additives remained localized and that the formation of binding structures occurred in an irregular manner. In a study supporting this finding, the effects of MICP applied through the mixing method on soil stabilization were investigated, and it was observed that CaCO\({}_{3}\) precipitates were unevenly distributed in both horizontal and vertical directions [38]. This heterogeneity was attributed to spatial variations in oxygen content, which influenced the mineralization reaction. Furthermore, the study emphasized that the mineralization process alters the pore structure of the soil, which is directly related to the stabilization efficiency of MICP-treated soils. The high concentrations of oxygen (49.16%) and silicon (28.86%) observed in EDS analysis indicate that the soil surface remains largely covered with natural silica. This suggests that the surface coating effect of SA and MICP products is limited. This finding is consistent with the irregular crystallization and weak binding effects observed in SEM images. The low calcium content indicates that sufficient calcite precipitation did not occur during the MICP process, which is likely due to the non-uniform distribution of SA within the soil matrix. Previous studies have emphasized that for the SA + MICP combination to produce effective results, the components must be applied to the soil in a controlled and layered manner [46; 47; 48]. According to EDS analysis, the presence of carbon (10.13%) and calcium (3.08%) indicates the formation of CaCO\({}_{3}\) as a result of the SA additive and the MICP process. However, this calcium content is lower than that observed in the S3-SA-MICP specimens treated via the injection method. This suggests that the additives applied through the mixing method were not homogeneously distributed within the coarse-grained S3 soil, and that calcite precipitation remained mostly confined to the surface.