Abstract: Calcareous sands are widely distributed in coastal areas around the world. They are considered as a material with low shear strength and high compressibility. Stabilizing calcareous sand has become a hot research topic in coastal geotechnics recently. Microbial induced calcite precipitation (MICP) is a new soil improvement technique. Currently, MICP is primarily implemented through the bio-augmentation approach, which is expensive and has a bad compatibility with the natural soil environment. This study focuses on the bio-stimulated MICP approach by enriching indigenous ureolytic bacteria to stabilize calcareous sand. Direct shear and one-dimensional compression tests are conducted on the bio-cemented samples. The results show that the bio-stimulated MICP approach could create up to 6.26% cementation level within the sand matrix. Increasing the concentration of cementation solution or treating multiple times could yield higher cementation level. during the direct shear test, the peak stress ratio, peak dilation angle, and near critical state friction angle increase significantly with elevated cementation level. However, these mechanical parameters could be suppressed at higher normal stress levels. Meanwhile, the compressibility of bio-cemented sand is significantly reduced with the increase in the cementation level. Upon the completion of the compression test, the proportions of both very fine and vary coarse particles increase with elevated cementation level.

Key words: calcareous sand, bio-mineralization, bio-stimulation, shear strength, compressibility