Experimental Research On Solidification Of Calcareous Sand Through Carbonate Precipitation Induced By Microbe And Rubber Materials

The South China Sea has always been an important sea area in China.Its special geographical location makes it of extremely special military strategic significance.The South China Sea Islands and reefs are the precious land area of the South China Sea.The special geological structure is that the calcareous sand composed of fragments such as coral debris is widely distributed,which is a kind of material with irregular shape,many pores,low strength and easy to break.In the construction and development of islands and reefs in the South China Sea,the traditional mechanical,physical and chemical methods to reinforce the foundation in the special geology of the South China Sea will encounter problems such as poor reinforcement effect,high cost and environmental pollution.However,the rise of MICP(microbial inducedcalcite precipitation)technology provides us with a new way to strengthen the calcareous sand foundation.If it can become a qualified calcareous sand foundation,it will provide theoretical research for many construction facilities in the South China Sea Islands and reefs,and the South China Sea is rich in sea water resources.If it can be used to cultivate microorganisms,it will bring huge benefits to the local economy and environment.The advantages of this technology are that the bacteria used are harmless and pollutionfree,will not cause damage to the environment,and no toxic substances are discharged during the MICP curing process.The physical properties and strength of the solidified calcium sand are good,which has more advantages than the traditional curing method.However,there are some defects in MICP technology.The solidified sand is self significant,brittle and poor uniformity,which leads to the unsatisfactory solidification effect.It has been found that adding rubber particles into the soil can significantly improve the impermeability of the soil,reduce the self weight of the soil,recycle the waste tires and save resources.In order to better apply rubber particles to microbial reinforcement technology and improve the effect of sand solidification,this paper uses MICP technology to study the effect of different rubber ratios on MICP solidified calcareous sand under certain conditions,such as concentration and configuration of bacterial solution and cementitious solution,grouting mode,number of reinforcement rounds and so on.Three rubber particle sizes of 0 ? 1mm,1 ? 2mm,2 ? 3mm and ten rubber contents of 0% ? 30% are selected to study the effect of different rubber ratios on MICP solidified calcareous sand Ring.This paper analyzes the solidified calcareous sand with different rubber content and particle size by four physical characteristics of calcium carbonate content,dry density,water absorption,permeability coefficient,unconfined compressive strength,dynamic shear modulus and damping ratio(1)Read the relevant literature in this field extensively,summarize the research status and development level of calcareous sand and microbial solidified sand at home and abroad,review the advantages and disadvantages and limitations of the existing research work,and put forward the further research ideas and solutions to the related problems.(2)The four physical properties of MICP curing calcareous sand mixed with rubber were studied through the tests of calcium carbonate content,dry density,water absorption and permeability.The effects of rubber content and rubber particle size on the properties were discussed.According to the test phenomena,the mechanism of these four physical properties changing with rubber content and rubber particle size was analyzed,and the rubber blending under different conditions was obtained Quantitative results of physical properties of cemented calcareous sand.(3)Based on the unconfined compression test,the strength characteristics of MICP solidified calcareous sand mixed with rubber were studied.From the qualitative and quantitative analysis,the process of structural damage,the characteristics of cleavage interface,and the regularity of unconfined compression strength changing with rubber content,rubber particle size and calcium carbonate content were investigated.The different rubber content,rubber particle size and calcium carbonate content were revealed The change mechanism of the strength characteristics of the cured sample.(4)Through GDS resonant column test,the dynamic shear modulus and damping ratio of solidified calcium sand with different rubber content and rubber particle size were analyzed,and the dynamic characteristics of MICP solidified calcium sand with rubber in small strain range were studied.According to the test phenomenon,the mechanism of these two dynamic characteristic indexes changing with the rubber content and rubber particle size is analyzed,and the dynamic shear modulus of the sample with rubber solidified calcareous sand is normalized by using Hardin-Drnevich hyperbolic model.On the basis of regression analysis,the hyperbolic model is modified to get the empirical fitting formula,which can be used for different samples with rubber mixed calcareous sand The trend of dynamic shear modulus changing with shear strain is predicted.