Microbially Induced Sand Cementation Method Using Pararhodobacter sp Strain SO1, Inspired by Beachrock Formation Mechanism

摘要

To develop an alternative ground improvement technique in coastal areas based on bio-stimulation, we investigated sand cementation using bacteria that have been shown to enhance beachrock formation. We conducted cementation tests using Pararhodobacter sp. strain SO1, a local ureolytic bacteria originating from the sand near beachrock in Okinawa, Japan. Specifically, we attempted to cement sand specimens to unconfined compressive strength (UCS) of several MPa and establish the influence of several test conditions (curing temperature, injection interval of cementation solution, Ca2+ concentration and sodium malate concentration in the cementation solution, and test period) on the UCS. Column specimens were cemented up to UCS of 10 MPa after 28 days under the conditions (curing temperature; 30 degrees C, injection interval; 1 day, Ca2+ concentrations in cementation solution; 0.3 M). Multiple regression analysis showed that the relevant conditions for UCS were test period, D (days), and Ca2+ concentration of the cementation solution, C-ua (M). The prediction formula for UCS, q(ud) (MPa), was experimentally determined to be q(ud) = 48.3C(ca) + 0.456D - 19.51. Overall, the results of this study will contribute to the application of a new technique for coastal sand improvement and bio-stimulation.