## 3 Results and Discussion
### Potentiality for Sand Solidification and Design for the Application  
The results of the temporal variation of Ca\({}^{2}\) + and the pH effluent is presented in Figure 8a,b, respectively. From the figure, it is shown that the Ca\({}^{2}\) + discharge liquid was seen to continue to rise from around 4 days from bacterial implantation and then decreased with time (Figure 8a). The Ca\({}^{2}\)+ concentration increased, indicating that the hydrolysis effect of the urea-degrading bacteria in the syringe no longer worked, and it was presumed that the injection of regular cells was required. The pH tended to increase and then decrease with time (Figure 8b) which indicated the variation of urea hydrolysis inside the syringe.  
The outcomes of the needle penetration test are summarized individually and shown in Figure 9. From the figure, it was observed that maximum USC around 1.8 MPa was obtained at the middle portion for the G3, G1, and G2 species. The top portion was moderately sol  
Figure 8: (**a**) Temporal variation of Ca\({}^{2+}\) and (**b**) pH in the effluent from solidification solution in days.  
Figure 7: (**a**) CaCO\({}_{3}\) precipitation trend of the isolated strains and (**b**) SEM images of the precipitated CaCO\({}_{3}\) of G1 species.  
1.3 MPa) and the bottom portion was solidified bearing UCS around 1.4 MPa (for G3). This was because maximum urea hydrolysis possibly occurred at the middle portion and precipitated crystal might have had more contact point to bind sand particles at this stage [35]. Another reason could be the variation of aerobic and anaerobic conditions in between the bottom portion and beneath the portion of the sample that might be responsible in decreasing the urease activity and/or crystal precipitation. Therefore, further investigation is required to improve the solidification condition.  
It is well known that the traditional geotubes are widely utilized for flood control, to prevent waterlogging conditions, and for coastal erosion protection. However, all of these conventional methods are not sustainable because of the various of UV rays that come from sunlight damage the geotube after a certain period of time, and protection of soil might be hampered and thus, consequently, the re-installing cost for geotube will be increased [36]. Nonetheless, the re-installing cost could be minimized by using the MICP method and the geotube following our proposed novel approach (Figure 10). By implementing this novel approach, it would be possible to strengthen the coastal structure because the geotube and solidified sand MICP will protect against the UV rays, helping it to remain for a longer period and being more sustainable than the conventional method. In our proposed implementation method, the total cost will be much lower compared to traditional methods, and local ureolytic bacteria will be used, which is more eco-friendly and will ensure long term sustainability of the coastal structures. This method can also be useful in a wider range of civil engineering implementations including paving, construction, and drainage.  
Figure 10: Proposed coastal erosion protection method.  
Figure 9: Comparison of estimated unconfined compressive strength (UCS) in each strain.