This paper aims at monitoring the improvement of sandy soil properties with biocementation through the microbially induced calcite precipitation (MICP) method with reaction accelerations by self-developed soybean urease enzymes. In this study, the concentration of calcium ions (Ca2+ ions as CaCl2) is varied at 50, 100, 250, and 500 mM to determine an optimum shear strength. The self-developed soybean urease enzymes of 20% by volume (v/v) are used to accelerate the MICP reaction to finish within 7 days. Based on real-time monitoring bender element system and direct shear tests, the optimum Ca2+ concentration is found as 250 mM. However, a detrimental effect occurs in case of high concentration of Ca2+ as CaCl2 (500 mM) because of solution acidification from high Cl− concentration. This condition lowers CaCO3 precipitation causing the reduction of biocementation process. At equivalent shear modulus, the biocementation time of MICP-based sand with acceleration by urease enzymes is about 10 times faster than that without. Using spectrophotometer and pH meter, the ammonification rate and the solution pH of biocemented sand with acceleration by urease enzymes for 3 days are found relatively higher than those without urease enzymes for 40 days. The analyses by scanning electron microscopy (SEM) and X-ray diffraction (XRD) confirm not only the occurrence of CaCO3 binding sand particles together but also the improvement of physical strengths of sandy soil samples with the MICP-based urease enzymatic acceleration method. These results introduce an option to accelerate biocemented sandy soil improvement.

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Soil biocementation is the new technology using biological process to initiate the crystal forms of carbonates to bind the soil particles resulting in soil mechanical improvement. This research examines the feasibility of microorganisms capable of hydrolyzing ammonia with production of carbonate collected from natural soil. The biocement was prepared by a mixture of calcium salt, urea, and microbial suspension collected from natural water samples. The urease activity was measured by the concentration of NH4+ in solution. The physico-chemical properties including the effects of Ca2+ concentrations, soil pH and crystal forming shapes were studied. The strength development of biocemented soil samples was measured by non-destructive test using shear wave velocity method. Formation of calcite layer on sand surface could be useful for the stabilization of the sand or earth structures.

Soil biocementation is the new technique using biochemical process to initiate the crystal forms of calcium carbonate (CaCO3) to bind the soil particles resulting in soil mechanical improvement. This research examines the effect of urease (UR) dosages on the strength development of sandy soil in biocemented sand reactor (BSR). Our results found that urease dosages between 5-30% (v/v) affected the strength development in sandy soil in term of shear modulus (G). Addition of UR resulted on an increase of solution pH. Highest solution pH during the treatment was found at UR 20%, as well as highest G value. Formation of CaCO3 in biocemented sand could be useful for the stabilization of the sand or earth structures.

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