Impact of bacterial biopolymer formation on hydraulic conductivity, erosion resistancem and seismic response of sands

Abstract

Use of microbial activities has garnered a huge interest in recent years, not only because of their ubiquitous processes occurring in natural geo-media, but also because of their versatility in applications to geo-engineering. In particular, in situ bacterial colonization and accumulation of biopolymers in subsurface have a profound effect on the physical and chemical properties of soils, influencing fluid flow and transport properties. However, the impact of bacterial biopolymer formation on soil properties as well as the physical properties of soft biopolymer itself remains poorly understood. This study presents detailed laboratory test results and interpretation of the insoluble polysaccharide biopolymer produced by model bacteria Leuconostoc mesenteroides and such biopolymer-grown and -accumulated sands. Firstly, the elastic characteristics of dextran with the shear modulus of ~0.1 Pa was confirmed by using particle-tracking microrheology. Secondly, the production and accumulation of insoluble biopolymer observed to lead to readily reduced hydraulic conductivity of sands by more than one order of magnitude and improved the erosion resistance of sands. Lastly, we examined the feasibility of using P- and S-wave responses for monitoring of biopolymer accumulation and permeability reduction in sands. This baseline experimental results presented here show how soft biopolymers formed by bacteria can modify and improve soil behaviors.