Meter-Scale Biocementation Experiments to Advance Process Control and Reduce Impacts: Examining Spatial Control, Ammonium By-Product Removal, and Chemical Reductions

Abstract

Microbially induced calcite precipitation (MICP) is a ground improvement technique that uses ureolytic bacteria to biocement soils by precipitating calcium carbonate on soil contacts and surfaces. In this study, five 3.7-m long horizontal columns, each containing 0.15 m3 of natural sand, were treated to address current knowledge gaps regarding the application of MICP at field-scale including investigating treatment extent, improvement of spatial uniformity, stimulation strategies, and posttreatment removal of ammonium by-products. Two stimulated columns containing poorly graded alluvial sand were treated to achieve high and low ureolytic rates to investigate differences in treatment uniformity and extent. An additional column with the same sand was augmented with Sporosarcina pasteurii targeting a high ureolytic rate similar to the high rate stimulated column. Two additional stimulated columns, containing poorly graded alluvial and marine sands, were treated to achieve a low ureolytic rate to evaluate the effect of soil mineralogy. Treatments were first applied to establish either indigenous or augmented microorganisms, after which all columns received nine cementation treatments. Following cementation, produced ammonium by-products were removed using a rinse solution injection and soil samples were obtained and analyzed for calcite content. During all treatments, solution urea and ammonium concentrations as well as soil hydraulic conductivities and shear wave velocities were monitored. In all columns, insignificant changes in permeability were observed during treatments despite Vs increases up to 1,325 m/s. Results suggest that improvements in the spatial uniformity and extent of biocementation can be achieved through the use of lower ureolytic rates that minimize reactions during injections.