Biocementation for Liquefaction Mitigation: Examining Response, Development, and Deployment

Abstract

Microbially Induced Calcite Precipitation (MICP) is an environmentally conscious soil improvement technique that can improve the geotechnical properties of granular soils through the precipitation of CaCO3 minerals on soil particle surfaces and contacts. The resulting biocementation affords significant improvements in soil shear strength and initial shear stiffness, while achieving minor reductions in soil hydraulic conductivity and porosity. The process has been investigated for wide variety of geotechnical and geoenvironmental applications, however, perhaps most notably the technology has been proposed for the mitigation of earthquake-induced soil liquefaction. Despite extensive demonstrations at the laboratory scale, critical gaps regarding our understanding of the undrained cyclic behavior of biocemented soils, the efficacy of treatment techniques at meter-scale, and the management of generated aqueous nitrogen by-products has limited practical adoption of the technology for liquefaction mitigation purposes. In this research, a series of experiments at both centimeter- and meter-scales were performed in combination with reactive transport modeling in order to (1) further characterize the liquefaction behaviors of biocemented sands including triggering and post-triggering responses, (2) develop new techniques that can control the enrichment of indigenous ureolytic microorganisms to improve cementation spatial uniformity and extent, (3) identify post-treatment processes by which ammonium by-products can be effectively removed, and (4) evaluate the success of the developed treatment techniques when applied over meter-scale treatment distances. The results of this work suggest that (1) the liquefaction triggering resistance of biocemented soils can be significantly improved with the addition of even small magnitudes of cementation (∆Vs > 25 m/s), however, improvements in post-triggering behaviors require higher magnitudes of cementation (∆Vs > 50 to 150 m/s), which can improve larger-strain behaviors by densifying soils in addition to providing interparticle bonding and cemented particle coatings, (2) enrichment techniques can be modified to regulate stimulated bulk ureolytic activities with the ability to achieve improved spatial control of the biocementation process, (3) ammonium by-products can be successively removed from soil particle surfaces and pore fluids using post-treatment rinse injections containing cations that permit improved cation exchange with sorbed ammonium masses, and (4) developed techniques can be successfully up-scaled to uniformly improve soils over meter-scale distances, effectively remove generated ammonium by-products, and realize mechanical enhancements far exceeding those needed for most liquefaction mitigation applications. The primary outcomes of this research identify novel and effective field-ready treatment techniques for stimulated MICP as well as provide new understandings regarding the deployment of MICP at meter-scale and the liquefaction behaviors of biocemented soils, ultimately furthering the development of the technology for practical liquefaction mitigation applications.