One-phase improvement of sandy soil using seawater-based soybean-induced carbonate precipitation

Seawater-based soybean-induced carbonate precipitation (SSICP) was proposed for sandy soil improvement. A series of comparative bio-cementation tests on Ottawa sand and sea sand through SSICP and deionized water-based soybean-induced carbonate precipitation (SICP) were carried out. Experimental results indicate that seawater can be used to extract soybean urease. It has a certain negative effect on urease activity, but SSICP method has better sand improvement performance. When the soybean powder concentration is 100 g/L and soaking time is 60 min, related urease activity exceeds 2.50 U. It increases as the soaking time increases before 60 min, and then decreases. Generally, urease activity of deionized water-extracted soybean urease is higher than that extracted by seawater. The compressive strength of SSICP bio-cemented Ottawa sand blocks reaches 401.67 kPa, which is about twice of that bio-cemented by SICP (191.62 kPa). The better sand improvement mechanism of the SSICP method can be attributed to the mixture of calcium carbonate and calcite magnesium produced by the SSICP process is beneficial to improve sand strength compared to calcite only produced by the SICP process. The performance of carbonate precipitation and bio-cementation on Ottawa sand is better than those on sea sand, resulting in lower compressive strength and carbonate content of sea sand blocks.