Study On Mechanical Properties Of MICP Treated Oil-contaminated Sand

Microbial Induced Carbonate Precipitation(MICP)technology has been widely used and paid attention to in the field of geotechnical engineering.This technology can not only effectively improve the strength,stiffness,and anti-erosion ability of geotechnical materials,but also maintain good water permeability after treatment,providing a good environment for the growth of plants.On the other hand,with the rapid development of China’s economy,the oil demand is growing.Oil leakage occurs sometimes in the process of oil exploration,transportation,loading and unloading,processing,and use.Once oil seeps into the soil,it will not only pollute the soil but also affect the engineering mechanical properties of the soil.Currently,the existing treatment methods of oil-contaminated soil around the world are relatively single,and cement solidification treatment is often used as the main treatment method.This paper proposes the use of MICP technology to treat oil-contaminated sand,which provides a new idea for the treatment of oil-contaminated sand in practical engineering.By using Bacillus pasteurii and cementation solution(mixed solution of urea and calcium chloride)and MICP technology,calcium carbonate crystals with cementation can be formed between sand particles to solidify sand.Through systematic strength and permeability tests on oil-contaminated and non-contaminated sand samples treated with MICP or cement,combined with the scanning electron microscope(SEM)and X-ray diffraction(XRD)tests,the influences and mechanism of MICP on mechanical properties of treated oil-contaminated sand were revealed from macro and micro perspectives.The main research work and conclusions are summarized as follows:(1)Obtain the basic parameters of microorganisms(bacterial optical density,bacterial activity)through relevant biochemical detection methods;using a selfdeveloped solidification device and low p H one-phase injection technology can effectively distribute the calcium carbonate produced uniformly and prepare a highstrength sand column.Through conventional indoor geotechnical tests,the basic physical property parameters are obtained;the sand pillars are treated by different cementing materials(cement and microorganisms),and oil-contaminated sand pillars with different contents(9%,11%,13%,15%)are prepared And non-polluting sand column samples,a detailed unconfined compression test plan,triaxial consolidation undrained shear test,and permeability test plan were formulated;the microscopic XRD and SEM were used to obtain the mineral composition and microstructure Morphological characteristics.(2)The optimized MICP solidification method was used to solidify oilcontaminated sand and non-polluted sand respectively,and the corresponding mechanical properties were compared.The strength was obtained by carrying out the unconfined compressive strength test and triaxial consolidation undrained shear test.Characteristics,the penetration characteristics are obtained by carrying out penetration tests.The results show that: under the same calcium carbonate content,the strength of MICP-treated oil-contaminated sand is weaker than that of MICP-treated noncontaminated sand.When the calcium carbonate content reaches about 15%,the UCS value of MICP-treated oil-contaminated sand is significant.Increase to 1MPa.It shows that bacteria can retain their activity in oil-contaminated sand,and the calcium carbonate produced by microorganisms can be effectively treated in the sand pores,which overcomes the adverse effect of oil hydrophobicity on the bacterial retention on the surface of sand particles.MICP can greatly improve oil pollution.The mechanical properties of sand.Compared with the permeability of the microbial treated oilcontaminated sand column,the permeability of the microbial oil-contaminated sand column with a calcium carbonate content of 9.05% was significantly lower by 45%.It can be seen from XRD and SEM that the main crystal types of MICP solidified oilcontaminated sand and non-contaminated sand are aragonite and calcite,indicating that oil pollutants do not affect the crystal types of calcium carbonate.(3)The optimized microbial solidification technology and the traditional cement solidification technology were used to separately solidify petroleum-contaminated sands,and the corresponding mechanical characteristics comparative test research was carried out.The results were obtained through the unconfined compressive strength test and the triaxial consolidation undrained shear test.Strength characteristics,the penetration characteristics are obtained by carrying out penetration tests.The results show that the permeability coefficient of cement-treated oil-contaminated sand is significantly lower than that of microbial-treated oil-contaminated sand by more than90% with a cement content of 9%.Microbial solidification can maintain the permeability of the sand after solidification,which is better Ensure continuous curing test.The strength of MICP-cured oil-contaminated sand pillars is stronger than that of cement-cured oil-contaminated sand pillars.Oil organic matter has a greater impact on cement-cured sand pillars.This is attributed to the physical entrapment of oil on the surface of sand particles,which delays the hydration of cement and hinders CH The nucleation and growth of MICP indicate that the oil-contaminated sand column is treated by MICP and can replace cement to provide a new technology for oilcontaminated areas.It can be seen from SEM that the surface of the sand particles of the MICP-treated oil-contaminated sand column is relatively smooth.The calcium carbonate produced is mainly deposited between the pores of the sand particles,and a smaller part is deposited on the surface of the sand particles,while the cement-treated oil contaminates the sand column.A small part of cement hydration products is cemented between sand particles,and most of them are cemented on the surface of sand particles and produce a certain degree of solid agglomeration,resulting in low strength of cement-treated oil-contaminated sand.