Experimental study on precipitation rate of MICP under low temperatures

The low deposition rate of microbial solidification technology in low temperatures often restricts its application. Bacillus megaterium is chosen, and by controlling the different temperatures and pH values, the growth characteristics and urease activities of such strain are analyzed, and the calcium carbonate precipitation yields under different temperature conditions are studied. By adding urea to nutrient solution and the domestication in low temperatures, the low precipitation rate is improved. Finally, the sand solidification tests are conducted to comparatively study the curing effect with adding urea to medium or the domestication of Bacillus megaterium in low temperatures. The results show that the higher the temperature, the faster the growth and reproduction of Bacillus megaterium and the stronger the urease activity. Low temperatures obviously inhibit its growth and urease activity. When pH is 8, the growth and reproduction of bacillus are the fastest, and the urease activity is the strongest. The higher the temperature, the higher the deposition rate. Adding urea to nutrient solution and the domestication of Bacillus megaterium in low temperatures both can obviously increase the speed of reproduction and precipitation yield, which can effectively solve the problem of lacking calcium carbonate precipitation at low temperatures. By combining the two methods, the increase in sediment yields is more obvious. Adding urea to nutrient solution and the domestication of Bacillus megaterium in low temperatures both can improve the effect of soil solidification, and at the same time, using the two methods together, the curing effect promotion is more obvious. Therefore, the study can effectively solve the problem that less precipitation at low temperatures will obstacle actual engineering application, and lay a solid foundation for the subsequent application of MICP technology at low temperatures.