Effects of urease-producing bacteria on permeability and strength control for sands

Abstract

In the ground improvement field, microbially induced carbonate precipitation (MICP) is a novel bio-based soil improvement technique. To apply this technique, the presence of an actual construction site is needed to clearly understand the strength of increment and permeability reduction mechanisms with the specific trend of bacterial species. In this study, constant head permeability tests were performed on the three species of urease-producing bacteria, which were isolated from land and sea (estuary and deep-seabed). Permeability control and strength increment effect were evaluated with the constant head permeability and cone penetration tests. In all the test cases, the hydraulic conductivity decreased with the increment of the number of cementation solution injections and finally reached to almost two orders decreased. Moreover, the difference in the bacterial species showed a different permeability trend of the hydraulic conductivity despite the same amount of biomineral being deposited. Thus, the type of bacterial species has different chemical deposit mechanisms. In contrast, strength enhancement is affected by the deposited biomineral volumes from the cementation solution with bacterial specific urease enzyme. Consequently, the application of MICP needs to select the appropriate bacterial species for each type of ground improvement.