Influences of bacteria solution sealing state on the reinforcement of silt by bio-cementation

WANG Wei;ZHAO Zhifeng;ZHU Xiaobo;College of Civil Engineering, Nanjing Forestry University;

bio-cementation;;marine silt;;bacteria solution sealing state;;reinforcement effect

Using Sporosarcina pasteurii for inducing calcium carbonate precipitation to strengthen soil has become new research focus in civil engineering. The sealing state of bacteria solution in soil affects the activity of microbe and has a direct impact on the reinforcement effect. Now, many researches concentrate on the sand treatment by bio-cementation although few scholars pay attention to the sealing status of microbe. Marine silt was treated by bio-cementation method in this study, in which bacteria solution was premixed with dry soil and then was followed by cementation solution percolation for several times. The sealing state of bacteria was changed by controlling the flow out of bacteria solution, and the effect of sealing time of bacteria solution on the bacterial activity was studied. The bacterial activity was determined by measuring the conductivity of the effluent. The results showed that the sealing time had an obvious impact on the bacterial activity. When the sealing time was increased, the bacteria activity was increased gradually. With the increase in percolation times of cementation solution, the influence of sealing time of bacteria solution on its activity was decreased. The reinforcement effect of samples treated with different bacterial solution sealing time was significantly different. The unconfined compress strength was increased from 819 kPa to 1 347 kPa as the sealing time was increased from 0 to 12 h. Besides, in the samples with short sealing time of bacteria, the quantity of precipitated calcium carbonate was lower. The best reinforcement effect appeared when the bacterial solution was sealed in the sample for 12 h and then the cementation solution was percolated immediately. However, when the setting time of bacteria was further increased from 12 to 24 h, the reinforcement effect was declined. In order to verify results, the comparative tests of different bacteria sealing time were carried out with the higher concentration of bacterial solution(OD value equal to 2.2).The result proved that the best reinforcement effect was also obtained in samples with bacteria sealing in sample for 12 h, which verified the above conclusions. Nevertheless, increasing the concentration of bacterial solution could not improve the reinforcement effect.