EFFECTIVENESS OF DECREASING PERMEABILITY AND INCREASING SHEAR STRENGTH OF SANDY SOIL USING EXOPOLYSACCHARIDE BIOPOLYMER

Abstract

Sand is a type of soil with high porosity and a tendency toward a high permeability rate and low shear strength, which often causes problems in terms of piping and low slope stability. Permeability and shear strength have a very close relationship with soil stability. In this paper, we analyzed the addition of the bacterial producer exopolysaccharide on sandy soil for increased instability. The addition of this bacterial producer is expected to improve soil stability by reducing its permeability and increasing its shear strength. To find an alternative approach to overcome the problems of low permeability and shear strength, experiments were conducted using five types of non-pathogenic inoculated bacterial producer, namely, Lactobacillus sakei, Agrobacterium tumifaciens, Bacillus subtilis, Pseudomonas sp, and Nitrobacter sp, added to five samples of river and beach sand. After 30 days of bacterial inoculation, the permeability of the sand samples was tested using a constant head test, and the shear strength was tested using a direct shear test, which was confirmed through scanning electron microscopy (SEM). Based on the permeability test, the permeability of the sand samples inoculated with Bacillus subtilis was reduced the most at 74.43%. Based on the direct shear test, the highest increase in shear strength, i.e., about 58.91%, was in the samples inoculated with Lactobacillus sakei. SEM photographs with 10,000 x magnification showed the presence of bacteria and the formation of extracellular polysaccharides in the walls of the sand, which affected the permeability reduction rate and increased the shear strength of the sand samples. Based on the permeability and shear strength results, it can be seen that the correlation between the two is weak, and thus when the shear strength of the sample increases, the permeability does not necessarily decrease; the correlation depends on the type and characteristics of the bacterial producer.