Research On Direct Mixing And Cementation Reinforcement Of Microorganisms And Soil

Microbial induced calcium carbonate precipitation(MICP)technology is an environmentally friendly,green,and sustainable new technology for soil reinforcement.It can be used for strengthening foundations,treating liquefied soil,and biological plugging,and has certain social and economic value.At present,the use of MICP technology to reinforce soil mainly adopts grouting method and infiltration method,and the treatment object is mainly sand with larger particle size.Due to its grouting sequence and strong dependence on grouting instruments,the grouting method is prone to blockage at the grouting port.In addition,the use of grouting method to reinforce soil has limitations.The infiltration method is not conducive to strengthening fine-grained soil due to the low permeability of the cementitious fluid.The strength difference between the upper and lower parts of the soil reinforced by infiltration method is large,the reinforcement is uneven,and the reinforcement effect is poor.By studying the one-time mixing method,which directly mixes microorganisms and cementitious substances to reinforce the soil,the problem of a single reinforcement method using MICP technology can be solved.This article studied the effects of bacterial morphology,bacterial activity,and bacterial concentration on MICP through solution experiments;The influence of different mixing methods on the reinforcement effect of sandy soil was compared;Explored the feasibility of magnesium oxide synergistically reinforcing soil with microorganisms;Explored the effects of magnesium oxide content,activity,and calcium chloride purity on the strength and water immersion stability of sandy soil;We have studied the reuse of industrial waste and the use of carbide slag combined with MICP technology to reinforce soil.The research work of this article is as follows:(1)A study was conducted on the impact of bacterial solution on the production and generation efficiency of calcium carbonate in a solution environment.The experiment was conducted using the centrifugation time and dilution ratio of the bacterial solution as variables.The results showed that in a solution environment,the urease activity of the bacterial solution after centrifugation was low in the early stage and high in the later stage.Centrifuge dilution method can reduce the reaction rate between the bacterial solution and the binder.When centrifuging the bacterial solution for 20 minutes,the efficiency of calcium carbonate generation is the highest.When the concentration of the adhesive solution is constant,the higher the activity of the bacterial solution,the higher the yield of calcium carbonate;A high concentration of bacteria can reduce the production of calcium carbonate.(2)The influencing factors of microbial and sand mixing and cementation reinforcement were studied.Conduct experiments on microbial mixing and cementation reinforcement of sandy soil using the concentration of cementitious substances and the number of infiltration rounds as the main variables.The results show that using the mixing infiltration method to reinforce sandy soil increases the calcium carbonate conversion efficiency with the increase of the amount of cementitious material used;However,excessive use of cementitious substances can inhibit bacterial activity,resulting in a decrease in the amount of calcium carbonate generated and conversion efficiency of the sample;The immersion stability and unconfined compressive strength of the sample increase with the increase of the number of infiltration rounds.(3)The influencing factors of magnesium oxide synergistic microbial reinforcement of sandy soil were studied by changing the content,activity,and purity of calcium chloride in magnesium oxide.Microbial mixing and reinforcement tests were conducted on sandy soil with the variables of magnesium oxide content,magnesium oxide activity,and calcium chloride purity.The results show that by adding a quantitative amount of magnesium oxide,under the combined action of magnesium carbonate,magnesium hydroxide,and calcium carbonate crystals,the pores of soil particles are effectively filled and cemented,and the unconfined compressive strength of the sample is improved;Its water stability has also been improved.The unconfined compressive strength of the sample increases with the increase of magnesium oxide content;The use of industrial grade calcium chloride instead of analyzing pure calcium chloride has a better reinforcement effect on the sample;The strength of the sample decreases with the increase of magnesium oxide activity.(4)A study was conducted on the impact of using industrial waste to synergistically reinforce soil with microorganisms.Conduct microbial mixing and reinforcement tests on sandy soil using the amount of calcium carbide slag as a variable.The results show that mixing calcium carbide slag powder with powder soil can improve the uniformity of the soil;The calcium oxide in calcium carbide slag can synergistically bind soil particles with microorganisms,effectively improving the water immersion stability of the sample;The strength of the sample increases with the increase of calcium carbide slag content.