Biogrouting of Rock Joints

Biogrouting using microbially induced carbonate precipitation (MICP) has advantages over cement grouting for rock joints as the particles of biogrout are much smaller than cement particles and thus can penetrate into very fine rock joints. In this study, we evaluate the performance of biogrout for the sealing of rock joints using model tests. A joint formed by two granite sheets of 0.07 m wide, 0.4 m long, and 0.01 m thick was biogrouted. The formation of biogrout in the joint was examined using 3D scanning and image reconstruction technology. The permeability reduction due to biogrouting was evaluated using the image analyses and numerical simulation. To evaluate the shear strength of the joint, direct shear tests conducted on cylindrical rock samples consisting of a horizontal joint treated using biogrout were also carried out. The tests have shown that the flow rate through rock joints can be reduced by up to 90% with 2~3 rounds of injection. The direct shear tests also demonstrated that peak shear strength of 4~7 MPa could be obtained after biogrouting for a planar rock joint with initially little shear strength. This study has shown that biogrout can be potentially used for rock joints to reduce seepage or enhance stability.