Compression behavior of MICP-treated sand with various gradations.

One-dimensional compression tests on quartz sands treated by microbially induced carbonate precipitation (MICP) were carried out to evaluate the effects of gradation and calcium carbonate (CaCO3) content on compression behaviors. The experimental results reveal that the compressibility of specimens increases with increasing coefficient of uniformity or decreasing CaCO3 content. The evolution of void ratio with vertical stress could be generally characterized into three stages based on the underlying mechanisms. The initiation of bond breakage occurs around vertical stress of 0.036 MPa, and the dominating mechanism transits to particle breakage around vertical stress of 8.3 MPa. Scanning electron microscope analyses demonstrate that bonding effect and coating effect of CaCO3 precipitation are responsible for the lower compressibility of MICP-treated specimen. The presence of small particles leads to more interparticle CaCO3 bonds whose breakage would still allow the small particles to fill the intercoarse-grain voids. [ABSTRACT FROM AUTHOR]