The application of bio-cementation for improvement in collapsibility of loess

Bio-cementation is currently appraised to solidify sandy soils, but only few studies use it to cement loess soil particles. The effects of the addition of loess soils on bacterial growth, urease activity, and productive rates for calcium carbonate were studied. Moreover, bio-cementation tests were conducted to improve the collapsibility of loess soils. The results showed that adding increased loess soils increased the pH of supernatant, while the addition of loess soils slightly affected the growth and urease activity of Sporosarcina pasteurii. The productive rates for calcium carbonate in samples treated with calcium chloride and calcium acetate are larger than those treated with calcium nitrate. The optimum concentrations of calcium ions and urea in the cementation solution for bio-cementation tests were 0.75 M and 1.0 M, respectively. The coefficients of collapsibility of samples with various initial densities all decreased via bio-cementation, but the decreasing ratios were different. The productive rates for calcium carbonate were larger for the samples with larger densities. The coefficients of collapsibility decreased with the increase in treatment cycles. Moreover, there were larger increasing ranges of productive rates for precipitation from 4 to 6 cycles. Adding bacterial suspension and cementation solution together enabled better treatment effects for the samples with smaller densities, however, while adding them separately was more suitable for the samples with larger densities.