Experimental Study On Restoration Of Site Soil Based On Microbial Mineralization Technology

City pile City Ruins site is a unique style of earthen sites in Kaifeng area.In the long history of thousands of years,Kaifeng City has been submerged in layers of loess after many floods and wars.Due to the high groundwater level,the site was buried deep and was not discovered until 1981.However,the present situation of City pile City Ruins site is not optimistic.Due to its location in the Yellow River flood area,City pile City Ruins site is mainly composed of silty clay,which is easy to disintegrate in water and has low mechanical properties.In recent years,with the decline of groundwater level and the subsidence of the ground,the underground part of City pile City Ruins site has been squeezed more and more seriously.In addition,Kaifeng area is hot and rainy in summer,and the climate is humid.The exposed part of the site is easy to be eroded by liquid water,and even collapse,disintegration and other adverse phenomena occur.Therefore,artificial protection and restoration are urgently needed.At present,the protection and restoration methods of site soil are often accompanied by high cost,inconvenient operation and environmental pollution.In recent years,microbial mineralization technology,with the advantages of environmental protection,high efficiency,wide application and simple operation,plays a more and more important role in the protection and restoration of earthen sites.In this paper,Kaifeng City pile City Ruins site soil as the research object,on the basis of the Yellow River Beach soil imitation site soil,mechanical properties and water stability as the breakthrough point,to explore the micp technology to repair and improve the City pile City Ruins site soil.The test contents and results are as follows1.Study on the preparation method of imitation site soil.It is found that the basic physical properties of the Yellow River Beach soil in Kaifeng are similar to those of City pile City Ruins site soil through the limit water content test and compaction test.Based on the site soil of City pile City Ruins site,the lack of Al₂O₃,Cao,Fe₂O₃,Mg O and other compounds in the Yellow River Beach soil were artificially supplemented.Finally,the imitative site soil with similar physical properties and chemical composition was obtained.2.To explore the best conditions of microbial mineralization technology.The growth characteristics of Bacillus Pasteurella were studied.It was found that the number and activity of bacteria increased logarithmically with time,and tended to be stable after 48 hours.The results showed that when the ratio of bacteria to gum was 1:1 and the concentration of cement was 1.5mol/L,the calcium carbonate precipitate was the most.When the temperature was 35 ? and p H= 9,urease had the strongest ability to hydrolyze urea.3.Improve the mechanical properties of the imitation site soil by drip method based on micp technology.The combination of dual phase cementation process and bacteria acidification mineralization method,drip treatment in horizontal rotation state,the reinforcement effect is remarkable.The unconfined compressive strength of the soil treated with p H = 5 bacterial solution,1.5mol/L cementation fluid and dropping alkaline buffer solution can reach 2.09 times of that of plain soil,which is 1.426 MPa,and the mass of calcium carbonate precipitate is 2.24 g.The mechanical properties of soil samples have been improved obviously,and they can bear more external stress.Through SEM observation,X-ray diffraction analysis and energy spectrum analysis,it can be seen that the product of mineralization reaction is calcite,which distributes evenly among soil particles and plays a good role in filling and cementation.4.Improve the water stability of imitation site soil by spraying method based on micp technology.There was no obvious change in the appearance of soil samples after treatment,and white spots would be formed when spraying too many times.After many times of treatment,the wetting index and disintegration rate of the soil samples were significantly reduced,the water stability was significantly improved,and the erosion effect of liquid water was greatly reduced,which effectively alleviated the adverse situation of collapse and disintegration.After 7 times of spraying,the comprehensive effect of 7 days curing soil sample is the best.The microstructure of the treated soil samples was observed by scanning electron microscope?SEM?.With the increase of spraying times and curing time,the amount of calcium carbonate precipitation on the soil surface was more,and the water stability was better.