Deformation of Microbial Induced Calcite Bonded Sands: A Micro-scale Investigation

Microbial induced calcite precipitation (MICP) is a novel ground improvement method that increases the strength and stiffness of sand using natural biogeochemical processes. This study investigates the mechanics of how microbial induced calcite bonds deform during loading. Surface energy measurements are conducted on silica and calcite substrates in order to assess whether the bonds experience a cohesive or adhesive failure. The results from the surface energy assessment indicate that calcite-calcite cohesion tends to be the weakest within the system and where the MICP bonded sands will likely fail. These findings are supported by particle contact loading tests, where two silica particles are bonded together through the MICP process, and the deformation of the silica particles and the calcite cement is monitored during shearing and axial loading. These results indicate the bond fails within the calcite phase. The results of the micro-scale study are then translated to the shear bands of a triaxial specimen of MICP sand. A triaxial specimen is cemented to a moderate level of MICP cementation, using shear wave velocity measurements as a process monitoring technique. The cementation degradation is monitored using shear wave velocity during drained shear and the thickness of the shear band is estimated. Scanning electron microscopy (SEM) is also used to evaluate the MICP bonded sand grains within and outside the shear band. The SEM results agree with the micro-scale investigation that cohesive failure appears to dominate during shearing.