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.

Artificial beachrock, formed by coral sand solidification through microbially induced carbonate precipitation (MICP), could provide coastal protection instead of concrete structures, and would be eco-friendly as well as help minimize costs. The present study was conducted to solidify coral sand through the MICP method by using an ureolytic bacterium (Parahodobacter sp.) isolated from peripheral beachrock. The goal was to obtain a sample with an unconfined compressive strength (UCS) of 20 MPa or more. We also aimed to examine the growth characteristics of this bacterium in the culture medium ZoBell2216E, which is commonly used for marine bacteria. In order to determine the suitability of the MICP test, growth properties of the microbial strain were observed under various culture conditions. A sand solidification test with MICP was carried out in a syringe as well as a PET cylinder. The strength of the resulting specimens was measured with the needle penetration test. The specimen solidified up to 20 MPa of the estimated UCS after 21 days of curing. For optimum growth of the bacterium, 1.0 g of the culture was added to100 mL culture media and incubated with shaking at 160 rpm. The preferred final concentration in solidification promoting solution of both urea and CaCl 2 was 0.5 M, with bacterial cell densities of 10 9 CFU/mL. In order to efficiently induce solidification, the optimum pH was 7.0 or higher, and Ca 2+ concentration was maintained at 1.0 g/L. The results were enhanced by re-injecting the culture solution when the pH and Ca 2+ concentrations in the specimen were not in the ideal ranges indicated above.

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Chemical grout is composed of a calcium phosphate compound (CPC) which develops to form calcium carbonate (CC) precipitation throughout the soil and leading to an increase in soil strength. In this paper, initially the condition for CPC precipitation by using different mixtures of calcium and phosphate stock solutions were investigated and analyzed. For that, Toyoura sand test pieces were cemented by CPC solutions and cured up to 28 days and carried out unconfined compressive strength (UCS) test. Moreover, Toyoura sand test pieces were cemented by CPCs with scallop shell (SS) powder and cured and these specimens also analyzed with UCS tests. The UCS of the sand test pieces cemented by CPC with SS powder was larger than that of the test pieces with no added powders. The UCS of Toyoura sand test piece cemented with the CPC-SS powder method increased to a maximum of 156.9 kPa. Moreover, the best CPC-Chem mixture for cementation is CA: DPP with the concentration of Ca/P ratio is 0.5. In addition pH concentration, scanning electron microscope (SEM), and density before and after curing were observed. The results indicate that the density and the pH concentration of the sand test pieces cemented by CPCs with SS powder were larger than that of the sand test pieces with no added powders. SEM images of test pieces cemented with CA: DPP mixture by addition of SS powders not clearly identified a crystal formation among particles of Toyoura sand.