微生物沉积碳酸钙固化珊瑚砂的试验研究

向珊瑚砂中注入巴斯德芽孢杆菌菌液、氯化钙和尿素的混合液，利用微生物沉积碳酸钙固化珊瑚砂；并对珊瑚砂固化体进行了渗透、强度及微观结构等试验。试验结果表明，巴斯德芽孢杆菌的活性随时间呈衰减趋势，但衰减速度缓慢，能较好地满足珊瑚砂固化的需要。随着菌液、氯化钙和尿素的混合液注入次数的增加，珊瑚砂柱渗透性逐步降低，最终渗透性降低了1～2个数量级。微生物固化后的珊瑚砂柱应力-应变曲线大致可分为3段，即应力随应变缓慢增加段、快速增加段以及突降段。试样发生压裂脆性破坏，无侧限抗压强度最高达到14 MPa左右。抗压强度随干密度增加而增大，随渗透性降低而增大。微生物固化后珊瑚砂颗粒被生成的碳酸钙完整的包裹，孔隙间极少见生成的碳酸钙，与普通硅砂微生物固化后的微观结构不同，较好地解释了渗透性降低不多的原因。

An experimental study of coral sand enhanced through microbially-induced precipitation of calcium carbonate

By injecting Pasteur bacillus suspension and CaCl2-urea solution, the coral sand was solidified through the microbially-induced precipitation of calcium carbonate. Then a series of experiments including the permeability, strength and microstructure tests was conducted on the solidified soil. It is shown that the bacteria activity of Pasteur bacillus decreases slowly with time elapsing, which satisfies the requirement of the improving coral sand. Due to the bio-mediated improvement, the permeability of coral sand pillars decreases by 1 to 2 orders in magnitude. The stress-strain curve of improved coral sand pillars can be divided into 3 stages: stress increasing slowly with strain, stress increasing fast with strain and stress suddenly falling with strain. The unconfined compressive strength of specimen is up to 14 MPa before specimens being compressed into brittle failure. The compressive strength increases with the increase of dry density and the decrease of permeability. Unlike the silica sand improved by microbe, the coral sand improved by the current technology has a structure that the calcium carbonate precipitates wholly around coral sand particles. Hence the bonding between two particles by calcium carbonate is relatively weak, which properly explains the insignificant decrease of permeability.