Factors Affecting Sand Solidification Using MICP with <i>Pararhodobacter</i> 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 solidi cation 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 uncon ned compressive strength (UCS) of more than several MPa to improve soil properties and investigate the in uence of various factors on the engineering properties of treated soil catalyzed by ureolytic bacteria (curing temperature, injection interval of cementation solution, Ca 2+ 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 C, an injection interval of 1 day, and a Ca 2+ 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 Ca 2+ 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.

Feasibility study for slope soil stabilization by microbial induced carbonate precipitation (MICP) using indigenous bacteria isolated from cold subarctic region

“…The UCS increases during MICP improvement as calcium carbonate precipitates and cements the soil particles, as a result of void space reduction. It is also clear that the UCS increases exponentially with the increase in calcium carbonate content, similar to that reported in previous studies [2,6,32].…”

“…grow from particle surface into pore space to create bridges between particles), when the soils are treated in saturated conditions [4,5,11]. Well coated grains with matrix supporting by calcite crystals are also often observed by many researchers in medium to coarse sands treated under saturated conditions [2,5,11,47]. It is worth noting that the microstructure reported herein for the specimens treated under percolation condition slightly differ from that reported for saturated conditions.…”

“…The columns of all the soils were packed to a dry density of 1.6 ± 0.1 g/cm 3 similar to that reported by Cheng and Cord-Ruwisch [3]. Reactants were injected in two subsequent phases as suggested by several MICP researchers [1,2,11]. In the first phase, the enriched bacteria culture was injected to the column followed by a time gap of 2 h to immobilize the bacteria cells with soil particles.…”

“…calcium carbonate cement is precipitated at the nucleation sites provided by the bacteria cells (Eq. 2) [1][2][3].…”

“…Despite being a relatively new technique, many MICP studies have been investigated for several geotechnical applications including liquefaction control, erosion mitigation, coastline preservation, sand dunes stabilization, borehole stabilization and settlement control [6][7][8][9]. Most of the investigations have been focused on the behavior of MICP treated sand, providing information on the strength and stiffness characteristics under different testing conditions [2,5,6,[9][10][11]. The studies to promote MICP applications need to be expanded, for soil types other than sand materials.…”