Factors Affecting Sand Solidification Using MICP with Pararhodobacter sp.

Abstract

Biomineralization is an environmentally friendly technology for improving soil-engineering properties. One of the most common biomineralization processes is microbially induced calcite precipitation (MICP). In this study, sand solidification tests were conducted using Pararhodobacter sp., which is a local ureolytic bacteria obtained from the sand near beach rock in Okinawa, Japan. The goal of this study was to solidify a specimen having an estimated unconfined compressive strength (UCS) of more than several MPa to improve soil properties and investigate the influence of various factors on the engineering properties of treated soil catalyzed by ureolytic bacteria (curing temperature, injection interval of cementation solution, Ca²⁺ concentration, curing time, bacterial population, re-injection of bacteria and particle size of sand). Model test specimens were cemented up to an estimated UCS of 10 MPa after 14 days under the following conditions: a curing temperature of 30℃, an injection interval of 1 day, and a Ca²⁺ concentrations in cementation solution of 0.5 M. Multiple regression analysis showed that the relevant conditions for estimating UCS were test period, D (days), and Ca²⁺ concentration of the cementation solution, C_ca (M). The formula for predicting the estimated UCS (q_eu (MPa)) was q_eu = 13.99 C_ca + 0.37 D − 0.09. Overall, the results of this study will contribute to the application of a new technique to sand improvement and bio-stimulation.