Experimental study on sand solidification using plant-derived urease-induced calcium carbonate precipitation

The plant-derived urease-induced calcium carbonate precipitation cemented sand is a new technology in the field of geotechnical engineering, which has many advantages over the currently widely-used technology of solidifying sand by microorganism. Urease is extracted from soybeans directly. At first, the effects of temperature and pH on soybean urease activity are studied. Then the tests on the urease-induced calcium carbonate precipitation are carried out by controlling gel solution concentration, pH, temperature and reaction time. Based on this, three kinds of sand with different particle sizes are solidified by injecting urease solution and gel solution circularly. The solidification effect is evaluated by ultrasonic tests, unconfined compressive strength tests and calcium carbonate production tests. The results show that the optimal pH of soybean urease is 8, and urease activity increases with the increase of temperature in the range of 15℃~75℃. The precipitation product induced by soybean urease is calcite. With the increase of gel solution concentration, the production rate of calcium carbonate increases first and then decreases, and when the gel solution concentration is 0.75 mol/L, the production rate of calcium carbonate is the highest. When the gel concentration is constant, the production rate of calcium carbonate is the highest at the pH of 8, and the production rate increases with the increase of reaction time. The temperature within 10℃~40℃ has little effect on the production rate of calcium carbonate. The compressive strength of solidified samples is positively correlated with the content of calcium carbonate. With the increase of the particle sizes of sand, the compressive strength of samples increases first and then decreases, and the sand with particle size of 0.25~0.5 mm has the best solidification effect.