Effects of calcium sources on the strength and water stability of loess solidified by soybean urease

The issues of severe soil and water loss and weak erosion resistance in the Loess Plateau region are primarily attributed to the low strength and poor water stability of loess. Soybean urease-induced calcium carbonate deposition is a green and low-carbon biological soil stabilization technology, in which the calcium source critically influences the mechanical and hydraulic properties of the solidified soil. Three calcium sources, calcium chloride, calcium acetate, and calcium nitrate, were selected to prepare cementation solutions for treating loess, with a control group established for comparative analysis of the solidification effects. A series of macro- and micro-tests were conducted on the loess solidified with different calcium sources to clarify the development patterns and interrelationships among macro- and micro-indicators, including strength, failure characteristics, disintegration evolution, calcium carbonate content (CCC), mineral composition, and micromorphology, under varying cementation solution concentrations and curing periods. The results demonstrate that the unconfined compressive strength (UCS) of calcium nitrate-solidified soil reached 1 857.24 kPa, approximately 1.91 times higher than that of the control group. The calcium chloride-solidified soil exhibited the best disintegration resistance, with disintegration time extended by up to nearly 3.52 times. The UCS and disintegration time of the solidified soil showed linear and exponential relationships with CCC, respectively. The calcite crystals induced by soybean urease reshape the microstructure of loess through cementation, filling, and encapsulation, enhancing particle compactness and overall integrity, thereby significantly improving the strength and water stability of loess. This study provides robust support for selecting the optimal calcium source in soybean urease-solidified loess.