Fixation Of Sporosarcina Pasteurii In Porous Medium Using Ca²⁺ Bridging And Cementation Of Sand By Biogrouting

Microbial mineralization is a widespread phenomenon in nature. Some bacteriastrains can induce biomineralization of calcium carbonate, which will improve themechanical properties of the rock and soil, and there is no pollution in the wholeprocess. Biological in-situ reinforcement technology is based on the principle ofmicrobial induced calcite precipitation（MICP) to enhance in-situ rock and soil.Compared with traditional cement reinforcement with pollution of groundwatersystem and destruction of ecological environment, MICP is a new, green andsustainable technology. It has been considered as an important research direction ofgeotechnical engineering, and has a wide application prospect.In this thesis, isolation and growth characteristics of indigenous Sporosarcinapasteurii, fixation of Sporosarcina pasteurii in porous medium using Ca2+bridgingand cementation of sand by biogrouting were studied. The main achievements aresummed as follows:At first, a ureolytic strain was isolated from soil using selective enrichmentculture and plate screening techniques, and it was identified as Sporosarcina pasteuriiby16S rDNA sequence analysis. Then its growth characteristics were alsoinvestigated. The results showed that the suitable growth conditions of theSporosarcina pasteurii were as follows: initial pH was9; inoculation volume was4%;culture temperature was35℃and rotation rate was200r/min.Furthermor, the laws of the fixation of Sporosarcina pasteurii in sand by bridgingwere studied. The results showed that calcium ion could obviously improve theamount of the bacteria fixed by bridging. Within limits, the more bacteria injection,the better bacteria were fixed. Solution seepage velocity impacted the process ofbacteria fixation, and there should be an optimum seepage velocity in porous media.Finally, on the basis of the conclusions of bacteria fixation, by using the three-step injection method, experiments of cementation of sand by biogrouting usingthe Sporosarcina pasteurii was carried out. After repeated grouting, with the maximumnumber of times of grounting being15, all of the sand samples were molded. Whencalcium carbonate precipitation was271.9g/L, the uniaxial compressive strength andpermeability coefficient of the sand sample was2.58MPa and0.019cm/s,respectively. As a whole, the uniaxial compressive strength were increased with theincrease in calcium carbonate content, however the distribution of calcium carbonatehad a significant influence on the uniaxial compressive strength. The permeabilitywas decreased with the increase in calcium carbonate content of the sand samples.