Compressibility characteristics of bio-cemented calcareous sand treated through the bio-stimulation approach

Calcareous sand is widely present in coastal areas around the world and is usually considered as a weak and unstable material due to its high compressibility and low strength. Microbial-induced calcium carbonate precipitation (MICP) is a promising technique for soil improvement. However, the commonly adopted bio-augmented MICP approach is in general less compatible with the natural soil environment. Thus, this study focuses on the bio-stimulated MICP approach, which is likely to enhance the dominance of ureolytic bacteria for longer period and thus is deemed more efficient. The main objective of this paper is to investigate the compressibility of calcareous sand treated by bio-stimulated MICP approach. In the current study, a series of one-dimension compression tests was conducted on bio-cemented sand prepared via bio-stimulation with different initial relative densities (Dr). Based on the obtained compression curves and particle size distribution (PSD) curves, the parameters including cementation content, the coefficient of compressibility (av), PSD, relative breakage (Br), and relative agglomeration (Ar) were discussed. The results showed that av decreased with the increasing cementation content. The bio-cemented sand prepared with higher initial Dr had smaller (approximately 20%–70%) av values than that with lower initial Dr. The specimen with higher initial Dr and higher cementation content resulted in smaller Br but larger Ar. Finally, a conceptual framework featuring multiple contact and damage modes was proposed.