Improvement in silty sand with enzyme-induced carbonate precipitation: laboratory model experiment

Enzyme-induced carbonate precipitation (EICP) is a promising method for the improvement in soil properties. In this study, a model test using a meter-scale soil model was carried out to investigate the feasibility and performance of using the EICP method for the improvement in silty sand. Crude urease derived from soybeans was used for the catalyzation of urea decomposition in the EICP process. Industrial-grade calcium chloride and fertilizer urea were used for the soil treatment. In the treatment process, 1.5 pore volume treatment liquid (3/4 0.67 mol/L urea-calcium chloride solution and 1/4 crude urease liquid) was circulated in the soil model through four perforated pipes as one treatment time. The soil model was treated with totally 5 times. The results showed that the average calcium carbonate content in the soil was around 0.5%. The content was relatively high in the area between the injection/extraction pipes and close to the pipes. Penetration tests with a cone-shape penetrometer were conducted in the soil model. It was found that the penetration resistance in the soil model increased with more treatment times. The distribution of penetration resistances was also consistent with the distribution of calcium carbonate content in the soil model. Soils samples were taken from the model box for triaxial CD tests after the treatments. There were 5.4 similar to 34.7% improvements in the peak deviatoric stresses as compared with the untreated soil. The friction angle increased from 24.0 degrees to 28.9 degrees, and cohesion increased from 0 to 3.5 kPa. The SEM and XRD analysis also demonstrated the presence of CaCO3 produced in the soil. The experimental results indicated that the EICP method had the potential to be used for the improvement in silty sand in engineering projects.

Automated summary

Enzyme-induced carbonate precipitation (EICP) is a promising method for improving soil properties, as demonstrated in this study using a meter-scale soil model to treat silty sand. The EICP treatment led to increased calcium carbonate content in the soil, improved penetration resistance, and enhanced peak deviatoric stresses and friction angle in triaxial CD tests. SEM and XRD analysis confirmed the presence of CaCO3 in the treated soil, indicating the potential of EICP for engineering applications in silty sand improvement.