Investigating challenges of in situ delivery of microbial-induced calcium carbonate precipitation (MICP) in fine-grain sands and silty sand

Abstract

Microbial-induced calcium carbonate precipitation (MICP) is a sustainable soil improvement method with the potential for improving the engineering properties of sand and silty soils and therefore their resistance to liquefaction-inducing events. Work presented herein experimentally investigates the changes in hydraulic conductivity of fine sands and silty sands as a result of MICP treatment. In addition, numerical modeling is conducted to assess the changes in allowable injection rate and radius of influence for the delivery of the MICP process at the field scale. The hydraulic conductivity of Nevada sand and silty sand with 15% fines content decreased through MICP application with the trend of reduction being similar for both soils. Numerical modeling results show that with the progress of the MICP process, injection rates can be increased for Nevada sand, but remain unchanged for Nevada sand with 15% silt content (after MICP treatment up to a shear wave velocity about 400 m/s.) The presence of fines by itself leads to generation of higher levels of pore-water pressure during the injection process, which necessitates higher strength improvement to prevent development of excessive plastic strains. Therefore, improvement in shear strength and stiffness relative to the magnitude of the hydraulic conductivity level and its rate of change during the MICP process is a key parameter in determining the radius of treatment.