Enzyme-Induced Carbonate Precipitation Using Yellow Soybean for Eco-Friendly Treatment of Expansive Soils

We conducted an experimental study on the swelling–shrinking characteristic of expansive soil treated with enzyme-induced carbonate precipitation (EICP) using yellow soybean. A series of tests including the free swell test, swelling rate test, swelling pressure test, and shrinking test were conducted on expansive soil specimens with various water contents and equimolar concentrations. The test results showed that EICP-treated expansive soil samples exhibited an obvious reduction in the magnitude of free swelling rate, swelling rate, swelling pressure, and shirking rate compared with the untreated one. This indicates that EICP using yellow soybean can effectively reduce the swell and shrink potential of expansive soil. The free swelling rate consistently decreases with the increasing equimolar concentration. A more remarkable reduction in swelling rate can be observed at a concentration of 1 mol/L compared with a less significant decrease at a higher concentration. The free swelling rate shows an ascending trend first and then a declining tendency with the increase of water content at higher equimolar concentrations. The influences of equimolar concentration and water content on the change of swelling rate for treated samples with applied loading pressures are insignificant. The swelling pressure reduces remarkably with increasing equimolar concentration and then tends to level off. The swelling pressure exhibits an ascending tendency with the increase of water content. The shrinking rate reduces more remarkably with equimolar concentration at first and then increases less remarkably, with an equimolar concentration of 2 mol/L exhibiting the lowest shrinking rate. The soil specimen with higher water content shows a higher value of shrinking rate than that with a lower one.