In most coastal and estuarine areas,tides easily cause surface erosion and even slope failure,resulting in severe land losses,deterioration of coastal infrastructure,and increased floods.The bio-cementation technique ...In most coastal and estuarine areas,tides easily cause surface erosion and even slope failure,resulting in severe land losses,deterioration of coastal infrastructure,and increased floods.The bio-cementation technique has been previously demonstrated to effectively improve the erosion resistance of slopes.Seawater contains magnesium ions(Mg^(2+))with a higher concentration than calcium ions(Ca^(2+));therefore,Mg^(2+)and Ca^(2+)were used together for bio-cementation in this study at various Mg^(2+)/Ca^(2+)ratios as the microbially induced magnesium and calcium precipitation(MIMCP)treatment.Slope angles,surface strengths,precipitation contents,major phases,and microscopic characteristics of precipitation were used to evaluate the treatment effects.Results showed that the MIMCP treatment markedly enhanced the erosion resistance of slopes.Decreased Mg^(2+)/Ca^(2+)ratios resulted in a smaller change in angles and fewer soil losses,especially the Mg^(2+)concentration below 0.2 M.The decreased Mg^(2+)/Ca^(2+)ratio achieved increased precipitation contents,which contributed to better erosion resistance and higher surface strengths.Additionally,the production of aragonite would benefit from elevated Mg^(2+)concentrations and a higher Ca^(2+)concentration led to more nesquehonite in magnesium precipitation crystals.The slopes with an initial angle of 53°had worse erosion resistance than the slopes with an initial angle of 35°,but the Mg^(2+)/Ca^(2+)ratios of 0.2:0.8,0.1:0.9,and 0:1.0 were effective for both slope stabilization and erosion mitigation to a great extent.The results are of great significance for the application of MIMCP to improve erosion resistance of foreshore slopes and the MIMCP technique has promising application potential in marine engineering.展开更多
This paper reviews and analyzes recent research development on bio-cementation for soil stabilization and wind erosion control.Bio-cement is a type of cementitious materials by adopting natural biological processes fo...This paper reviews and analyzes recent research development on bio-cementation for soil stabilization and wind erosion control.Bio-cement is a type of cementitious materials by adopting natural biological processes for geotechnical and construction applications.Bio-cementation is usually achieved through microbially-or en-zymeinduced carbonate precipitation(MICP or EICP).The use of soybean urease can be a cost-effective solution for carbonate precipitation and bio-cementation,which is named SICP.The produced calcium carbonate can cement soil particles and bring considerable strength improvement to soils.In this paper,the mechanisms and recent development on the technology optimization are reviewed first.The optimization of bio-cementation involves 1)altering the treatment materials and procedures such as using lysed cells,low pH,the salting-out technique;and 2)using cheap and waste materials for bio-cement treatment and bacterial cultivation.The objectives are to improve treatment uniformity and efficiency,use bio-cement in more scenarios such as finegrain soils,and reduce costs and environmental impacts,etc.Studies on the mechanical behaviour and wind erosion performances of bio-cemented soil show that the wind erosion resistance can be improved significantly through the bio-cement treatment.In addition,the use of optimized method and additives such as xanthan gum and fibers can further enhance the strength,treatment uniformity or ductility of the bio-cemented soils.Attention should be paid to wind forces with saltating particles which have much stronger destructive effect than pure wind,which should be considered in laboratory tests.Field studies indicate that bio-cement can improve soil surface strength and wind erosion resistances effectively.Besides,local plants can germinate and grow on bio-cemented soil ground with low-concentration treatments.展开更多
The microbial-induced calcite precipitation(MICP)technique has been developed as a sustainable methodology for the improvement of the engineering characteristics of sandy soils.However,the efficiency of MICP-treated s...The microbial-induced calcite precipitation(MICP)technique has been developed as a sustainable methodology for the improvement of the engineering characteristics of sandy soils.However,the efficiency of MICP-treated sand has not been well established in the literature considering cyclic loading under undrained conditions.Furthermore,the efficacy of different bacterial strains in enhancing the cyclic properties of MICP-treated sand has not been sufficiently documented.Moreover,the effect of wetting-drying(WD)cycles on the cyclic characteristics of MICP-treated sand is not readily available,which may contribute to the limited adoption of MICP treatment in field applications.In this study,strain-controlled consolidated undrained(CU)cyclic triaxial testing was conducted to evaluate the effects of MICP treatment on standard Ennore sand from India with two bacterial strains:Sporosarcina pasteurii and Bacillus subtilis.The treatment durations of 7 d and 14 d were considered,with an interval of 12 h between treatments.The cyclic characteristics,such as the shear modulus and damping ratio,of the MICP-treated sand with the different bacterial strains have been estimated and compared.Furthermore,the effect of WD cycles on the cyclic characteristics of MICP-treated sand has been evaluated considering 5–15 cycles and aging of samples up to three months.The findings of this study may be helpful in assessing the cyclic characteristics of MICP-treated sand,considering the influence of different bacterial strains,treatment duration,and WD cycles.展开更多
In order to promote the development and utilization of desert sand,this study is based on researching the most suitable ratio of bio-cement,analyzing the shear strength and permeability of improved desert sand by comb...In order to promote the development and utilization of desert sand,this study is based on researching the most suitable ratio of bio-cement,analyzing the shear strength and permeability of improved desert sand by combining bio-cement and fly ash,and clarifying the applicability of tap water in bio-cement.The relationship between the two and the microstructural properties was investigated using the results of the straight shear test and the permeability test.The results showed that the urease solution prepared with tap water had a more pronounced temperature resistance.The urea concentration and the corresponding pH environment had a direct effect on the urease activity.The calcium carbonate yield was positively correlated with the calcium concentration,and the urea concentration was higher in the ranges of 1.0-1.5 mol/L.As the enzyme-to-gel ratio decreased,the calcium carbonate precipitate produced per unit volume of urease solution gradually converged to a certain value.The shear strength(increased by 37.9%)and permeability(decreased by about 8.9-68.5%)of the modified desert sand peaked with the increase in fly ash content.The microscopic test results indicated that the fly ash could provide nucleation sites for the bio-cement,effectively improving the mechanical properties of the desert sand.The crystal types of calcium carbonate in the modified desert sand were calcite and aragonite,which were the most stable crystal types.This study provides innovative ideas for interdisciplinary research in the fields of bioengineering,ecology and civil engineering.展开更多
Bio-cemented soils can exhibit various types of microstructure depending on the relative position of the carbonate crystals with respect to the host granular skeleton.Different microstructures can have different effec...Bio-cemented soils can exhibit various types of microstructure depending on the relative position of the carbonate crystals with respect to the host granular skeleton.Different microstructures can have different effects on the mechanical and hydraulic responses of the material,hence it is important to develop the capacity to model these microstructures.The discrete element method(DEM)is a powerful numerical method for studying the mechanical behaviour of granular materials considering grain-scale features.This paper presents a toolbox that can be used to generate 3D DEM samples of bio-cemented soils with specific microstructures.It provides the flexibility of modelling bio-cemented soils with precipitates in the form of contact cementing,grain bridging and coating,and combinations of these distribution patterns.The algorithm is described in detail in this paper,and the impact of the precipitated carbonates on the soil microstructure is evaluated.The results indicate that carbonates precipitated in different distribution patterns affect the soil microstructure differently,suggesting the importance of modelling the microstructure of bio-cemented soils.展开更多
Calcareous sand is widely present in coastal areas around the world and is usually considered as a weak and unstable material due to its high compressibility and low strength.Microbial-induced calcium carbonate precip...Calcareous sand is widely present in coastal areas around the world and is usually considered as a weak and unstable material due to its high compressibility and low strength.Microbial-induced calcium carbonate precipitation(MICP)is a promising technique for soil improvement.However,the commonly adopted bio-augmented MICP approach is in general less compatible with the natural soil environment.Thus,this study focuses on the bio-stimulated MICP approach,which is likely to enhance the dominance of ureolytic bacteria for longer period and thus is deemed more efficient.The main objective of this paper is to investigate the compressibility of calcareous sand treated by bio-stimulated MICP approach.In the current study,a series of one-dimension compression tests was conducted on bio-cemented sand pre-pared via bio-stimulation with different initial relative densities(D r).Based on the obtained compression curves and particle size distribution(PSD)curves,the parameters including cementation content,the coefficient of compressibility(a v),PSD,relative breakage(B r),and relative agglomeration(A r)were discussed.The results showed that a v decreased with the increasing cementation content.The bio-cemented sand prepared with higher initial D r had smaller(approximately 20%e70%)a v values than that with lower initial D r.The specimen with higher initial D r and higher cementation content resulted in smaller B r but larger A r.Finally,a conceptual framework featuring multiple contact and damage modes was proposed.展开更多
Soil improvement is one of the most important issues in geotechnical engineering practice.The wide application of traditional improvement techniques(cement/chemical materials)are limited due to damage ecological en-vi...Soil improvement is one of the most important issues in geotechnical engineering practice.The wide application of traditional improvement techniques(cement/chemical materials)are limited due to damage ecological en-vironment and intensify carbon emissions.However,the use of microbially induced calcium carbonate pre-cipitation(MICP)to obtain bio-cement is a novel technique with the potential to induce soil stability,providing a low-carbon,environment-friendly,and sustainable integrated solution for some geotechnical engineering pro-blems in the environment.This paper presents a comprehensive review of the latest progress in soil improvement based on the MICP strategy.It systematically summarizes and overviews the mineralization mechanism,influ-encing factors,improved methods,engineering characteristics,and current field application status of the MICP.Additionally,it also explores the limitations and correspondingly proposes prospective applications via the MICP approach for soil improvement.This review indicates that the utilization of different environmental calcium-based wastes in MICP and combination of materials and MICP are conducive to meeting engineering and market demand.Furthermore,we recommend and encourage global collaborative study and practice with a view to commercializing MICP technique in the future.The current review purports to provide insights for engineers and interdisciplinary researchers,and guidance for future engineering applications.展开更多
Loose sand particles could be cemented to sandstone by bio-cement（microbial induced magnesium carbonate）. The bio-sandstone was firstly prepared, and then the compressive strength and the porosity of the sandstone c...Loose sand particles could be cemented to sandstone by bio-cement（microbial induced magnesium carbonate）. The bio-sandstone was firstly prepared, and then the compressive strength and the porosity of the sandstone cemented by microbial induced magnesium carbonate were tested to characterize the cementation effectiveness. In addition, the formed mineral composition and the microstructure of bio-sandstone were analyzed by X-ray diffraction（XRD） and scanning electron microscopy（SEM）, respectively. The experimental results show that the feasibility of binding loose sand particles using microbial induced magnesium carbonate precipitation is available and the acquired compressive strength of bio-sandstone can be excellent at certain ages. Moreover, the compressive strength and the porosity could be improved with the increase of microbial induced magnesium carbonate content. XRD results indicate that the morphology of magnesium carbonate induced by microbe appears as needles and SEM results show that the cementation of loose sand particles to sandstone mainly relies on the microbial induced formation of magnesium carbonate precipitation around individual particles and at particle-particle contacts.展开更多
Microbial-induced carbonate precipitation(MICP)and enzyme-induced carbonate precipitation(EICP)are two bio-cementation techniques,which are relatively new methods of ground improvement.While both techniques share some...Microbial-induced carbonate precipitation(MICP)and enzyme-induced carbonate precipitation(EICP)are two bio-cementation techniques,which are relatively new methods of ground improvement.While both techniques share some similarities,they can exhibit different overall behaviours due to the differences in urease enzyme sources and treatment methods.This paper presented 40 unconfined compressive strength(UCS)tests of MICP and EICP treated sand specimens with similar average calcium carbonate(CaCO3)content subjected to cycles of wetting-drying(WD),freezing-thawing(FT)and elevated temperature(fire resistance test e FR and thermogravimetric analysis e TG).The average CaCO3 content after a certain number of WD or FT cycles(ACn)and their corresponding UCS(qn)reduced while the mass loss increased.The EICP treated sand specimens appeared to exhibit a lower resistance to WD and FT cycles than MICP treated specimens possibly due to the presence of unbonded or loosely bonded CaCO3 within the soil matrix,which was subsequently removed during the wetting(during WD)or thawing(during FT)process.FR test and TG analysis showed a significant loss of mass and reduction in CaCO3 content with increased temperatures,possibly due to the thermal decomposition of CaCO3.A complete deterioration of the MICP and EICP treated sand specimens was observed for temperatures above 600C.The observed behaviours are complex and theoretical understanding is far behind to develop a constitutive model to predict qn.Therefore,a multi-objective evolutionary genetic algorithm(GA)that deals with pseudo-polynomial structures,known as evolutionary polynomial regression(EPR),was used to seek three choices from millions of polynomial models.The best EPR model produced an excellent prediction of qn with a minimum sum of squares error(SSE)of 2.392,mean squared error(MSE)of 0.075,root mean square error(RMSE)of 0.273 and a maximum coefficient of determination of 0.939.展开更多
Geotechnical research has been yearning for revolutionary innovations that could bring breakthroughs to conventional practices,especially at a time when energy efficiency and environmental sustainability are of unprec...Geotechnical research has been yearning for revolutionary innovations that could bring breakthroughs to conventional practices,especially at a time when energy efficiency and environmental sustainability are of unprecedented importance in the field.Recently,exciting opportunities emerged utilising microorganisms,the ubiquitous soil dwellers,to provide solutions to many geotechnical problems,prompting the development of the new,multidisciplinary subject of biogeotechnics.Research interest has been centred on the use of microbially induced carbonate precipitation(MICP)to improve the engineering properties of soils.The present work aims to comprehensively review the progress of more than a decade of research on the application of MICP in soil strengthening.Through elucidation of underlying mechanisms,compilation and interpretation of experimental findings,and in-depth discussion on pivotal aspects,with reference made to key published studies,a holistic picture of the state of the art of MICP-based soil strengthening is drawn.Current knowledge gaps are identified,and suggestions for future research are given,along with the opportunities and challenges that lie ahead of practically implementing this technique in real-world geotechnical applications.展开更多
Soil liquefaction is a major geo-hazard.As liquefaction could occur anywhere in a sand layer and result in large-scale lateral spreading,treatment for liquefaction needs to be carried out over a large extent.The cost-...Soil liquefaction is a major geo-hazard.As liquefaction could occur anywhere in a sand layer and result in large-scale lateral spreading,treatment for liquefaction needs to be carried out over a large extent.The cost-effectiveness of the treatment then becomes a major consideration.With the development of microbial geotechnologies,some new approaches for liquefaction mitigation have been developed.Some of the methods offer more advantages over the existing methods.This paper gives an overview of the recent progress in bio related soil liquefaction mitigation methods.These include both bio-cementation and biogas desaturation.The mechanisms of bio-cementation and biogas desaturation are discussed.Recent up-scaled model tests and field trials are also reviewed.The studies so far have demonstrated that there is a great potential for some of liquefaction mitigation methods to be adopted in practice,although there are still challenges that need to be studied further.These include treatment efficiency,long-term sustainability,and biosafety.A brief introduction to some emerging technologies for liquefaction mitigation such as bio-gelation and use of fungi are also introduced.展开更多
A new and more ecologically sound cementing material known as“bio-cement”has been found to have the capacity to consolidate loose gravel into sand columns offering a certain degree of strength,and to fill and repair...A new and more ecologically sound cementing material known as“bio-cement”has been found to have the capacity to consolidate loose gravel into sand columns offering a certain degree of strength,and to fill and repair cracks in concrete to restore resilience.The typical representative is the microbial induced calcium carbonate deposition technology(MICP)and enzyme induced calcite precipitation(EICP).As part of this research,EICP with soybean urease as the core was studied.The test results show that soybean urease activity is significantly affected by pH and urea concentration values,while the external nickel source is not found to impair a stimulating effect on activity.When the concrete specimens were immersed in the composite solution of soybean urease,urea,and calcium chloride after having been subjected to a high temperature,a continuous layer of white precipitations quickly appeared on the surface of the specimens.Measured using a metalloscope,the thickness of the precipitations was found to reach up to 2.0 mm,while the surface water absorption rate was reduced by 70%.The effects of this combined outcome are believed to significantly protect and improve the durability of the concrete specimens previously subjected to a high temperature.At the same time,the composite solution is shown to be capable of cementing fly ash,with the cubic strength of the finished samples reaching 4.0 MPa after 3 days.Results from the use of a scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and X-ray diffraction(XRD),reveal that both the white precipitations on the surface of the concrete specimens and the cement binding the fly ash particles are calcite crystals.It is concluded from these preliminary study results that the use of soybean urease as a bio-cement had proved successful.展开更多
基金funded by the National Natural Science Foundation of China(Grant No.51578147)Fundamental Research Funds for the Central Universities(Grant No.2242020R20025)Ningxia Science and Technology Department(Grant No.2020BFG02014).
文摘In most coastal and estuarine areas,tides easily cause surface erosion and even slope failure,resulting in severe land losses,deterioration of coastal infrastructure,and increased floods.The bio-cementation technique has been previously demonstrated to effectively improve the erosion resistance of slopes.Seawater contains magnesium ions(Mg^(2+))with a higher concentration than calcium ions(Ca^(2+));therefore,Mg^(2+)and Ca^(2+)were used together for bio-cementation in this study at various Mg^(2+)/Ca^(2+)ratios as the microbially induced magnesium and calcium precipitation(MIMCP)treatment.Slope angles,surface strengths,precipitation contents,major phases,and microscopic characteristics of precipitation were used to evaluate the treatment effects.Results showed that the MIMCP treatment markedly enhanced the erosion resistance of slopes.Decreased Mg^(2+)/Ca^(2+)ratios resulted in a smaller change in angles and fewer soil losses,especially the Mg^(2+)concentration below 0.2 M.The decreased Mg^(2+)/Ca^(2+)ratio achieved increased precipitation contents,which contributed to better erosion resistance and higher surface strengths.Additionally,the production of aragonite would benefit from elevated Mg^(2+)concentrations and a higher Ca^(2+)concentration led to more nesquehonite in magnesium precipitation crystals.The slopes with an initial angle of 53°had worse erosion resistance than the slopes with an initial angle of 35°,but the Mg^(2+)/Ca^(2+)ratios of 0.2:0.8,0.1:0.9,and 0:1.0 were effective for both slope stabilization and erosion mitigation to a great extent.The results are of great significance for the application of MIMCP to improve erosion resistance of foreshore slopes and the MIMCP technique has promising application potential in marine engineering.
基金supported by the National Natural Science Foundation of China(Grant No.51978244,52078188).
文摘This paper reviews and analyzes recent research development on bio-cementation for soil stabilization and wind erosion control.Bio-cement is a type of cementitious materials by adopting natural biological processes for geotechnical and construction applications.Bio-cementation is usually achieved through microbially-or en-zymeinduced carbonate precipitation(MICP or EICP).The use of soybean urease can be a cost-effective solution for carbonate precipitation and bio-cementation,which is named SICP.The produced calcium carbonate can cement soil particles and bring considerable strength improvement to soils.In this paper,the mechanisms and recent development on the technology optimization are reviewed first.The optimization of bio-cementation involves 1)altering the treatment materials and procedures such as using lysed cells,low pH,the salting-out technique;and 2)using cheap and waste materials for bio-cement treatment and bacterial cultivation.The objectives are to improve treatment uniformity and efficiency,use bio-cement in more scenarios such as finegrain soils,and reduce costs and environmental impacts,etc.Studies on the mechanical behaviour and wind erosion performances of bio-cemented soil show that the wind erosion resistance can be improved significantly through the bio-cement treatment.In addition,the use of optimized method and additives such as xanthan gum and fibers can further enhance the strength,treatment uniformity or ductility of the bio-cemented soils.Attention should be paid to wind forces with saltating particles which have much stronger destructive effect than pure wind,which should be considered in laboratory tests.Field studies indicate that bio-cement can improve soil surface strength and wind erosion resistances effectively.Besides,local plants can germinate and grow on bio-cemented soil ground with low-concentration treatments.
基金the financial support provided by the Ministry of Education(MoE),Government of IndiaThe second author acknowledges Coal India Limited for providing financial assistance for the research(Project No.CIL/R&D/01/73/2021).
文摘The microbial-induced calcite precipitation(MICP)technique has been developed as a sustainable methodology for the improvement of the engineering characteristics of sandy soils.However,the efficiency of MICP-treated sand has not been well established in the literature considering cyclic loading under undrained conditions.Furthermore,the efficacy of different bacterial strains in enhancing the cyclic properties of MICP-treated sand has not been sufficiently documented.Moreover,the effect of wetting-drying(WD)cycles on the cyclic characteristics of MICP-treated sand is not readily available,which may contribute to the limited adoption of MICP treatment in field applications.In this study,strain-controlled consolidated undrained(CU)cyclic triaxial testing was conducted to evaluate the effects of MICP treatment on standard Ennore sand from India with two bacterial strains:Sporosarcina pasteurii and Bacillus subtilis.The treatment durations of 7 d and 14 d were considered,with an interval of 12 h between treatments.The cyclic characteristics,such as the shear modulus and damping ratio,of the MICP-treated sand with the different bacterial strains have been estimated and compared.Furthermore,the effect of WD cycles on the cyclic characteristics of MICP-treated sand has been evaluated considering 5–15 cycles and aging of samples up to three months.The findings of this study may be helpful in assessing the cyclic characteristics of MICP-treated sand,considering the influence of different bacterial strains,treatment duration,and WD cycles.
基金financially supported by National Natural Science Foundation of China(Grant no.42372323 and 42072319).
文摘In order to promote the development and utilization of desert sand,this study is based on researching the most suitable ratio of bio-cement,analyzing the shear strength and permeability of improved desert sand by combining bio-cement and fly ash,and clarifying the applicability of tap water in bio-cement.The relationship between the two and the microstructural properties was investigated using the results of the straight shear test and the permeability test.The results showed that the urease solution prepared with tap water had a more pronounced temperature resistance.The urea concentration and the corresponding pH environment had a direct effect on the urease activity.The calcium carbonate yield was positively correlated with the calcium concentration,and the urea concentration was higher in the ranges of 1.0-1.5 mol/L.As the enzyme-to-gel ratio decreased,the calcium carbonate precipitate produced per unit volume of urease solution gradually converged to a certain value.The shear strength(increased by 37.9%)and permeability(decreased by about 8.9-68.5%)of the modified desert sand peaked with the increase in fly ash content.The microscopic test results indicated that the fly ash could provide nucleation sites for the bio-cement,effectively improving the mechanical properties of the desert sand.The crystal types of calcium carbonate in the modified desert sand were calcite and aragonite,which were the most stable crystal types.This study provides innovative ideas for interdisciplinary research in the fields of bioengineering,ecology and civil engineering.
基金support from the China Scholarship Council(CSC)and the Geo-Engineering Section of Delft University of Technology.
文摘Bio-cemented soils can exhibit various types of microstructure depending on the relative position of the carbonate crystals with respect to the host granular skeleton.Different microstructures can have different effects on the mechanical and hydraulic responses of the material,hence it is important to develop the capacity to model these microstructures.The discrete element method(DEM)is a powerful numerical method for studying the mechanical behaviour of granular materials considering grain-scale features.This paper presents a toolbox that can be used to generate 3D DEM samples of bio-cemented soils with specific microstructures.It provides the flexibility of modelling bio-cemented soils with precipitates in the form of contact cementing,grain bridging and coating,and combinations of these distribution patterns.The algorithm is described in detail in this paper,and the impact of the precipitated carbonates on the soil microstructure is evaluated.The results indicate that carbonates precipitated in different distribution patterns affect the soil microstructure differently,suggesting the importance of modelling the microstructure of bio-cemented soils.
基金This study was financially supported by the Natural Science Foundation of China(Grant No.42007246)the Fundamental Research Funds for the Central Universities(Grant No.2242022k30055)Indo-U.S.Science and Technology Forum(Grant No.IUSSTF/AUG/JC/047/2018).
文摘Calcareous sand is widely present in coastal areas around the world and is usually considered as a weak and unstable material due to its high compressibility and low strength.Microbial-induced calcium carbonate precipitation(MICP)is a promising technique for soil improvement.However,the commonly adopted bio-augmented MICP approach is in general less compatible with the natural soil environment.Thus,this study focuses on the bio-stimulated MICP approach,which is likely to enhance the dominance of ureolytic bacteria for longer period and thus is deemed more efficient.The main objective of this paper is to investigate the compressibility of calcareous sand treated by bio-stimulated MICP approach.In the current study,a series of one-dimension compression tests was conducted on bio-cemented sand pre-pared via bio-stimulation with different initial relative densities(D r).Based on the obtained compression curves and particle size distribution(PSD)curves,the parameters including cementation content,the coefficient of compressibility(a v),PSD,relative breakage(B r),and relative agglomeration(A r)were discussed.The results showed that a v decreased with the increasing cementation content.The bio-cemented sand prepared with higher initial D r had smaller(approximately 20%e70%)a v values than that with lower initial D r.The specimen with higher initial D r and higher cementation content resulted in smaller B r but larger A r.Finally,a conceptual framework featuring multiple contact and damage modes was proposed.
基金funded by the National Natural Science Foundation of China(No.41962016)the Natural Science Foundation of NingXia(Nos.2023AAC02023,2023A1218,and 2021AAC02006).
文摘Soil improvement is one of the most important issues in geotechnical engineering practice.The wide application of traditional improvement techniques(cement/chemical materials)are limited due to damage ecological en-vironment and intensify carbon emissions.However,the use of microbially induced calcium carbonate pre-cipitation(MICP)to obtain bio-cement is a novel technique with the potential to induce soil stability,providing a low-carbon,environment-friendly,and sustainable integrated solution for some geotechnical engineering pro-blems in the environment.This paper presents a comprehensive review of the latest progress in soil improvement based on the MICP strategy.It systematically summarizes and overviews the mineralization mechanism,influ-encing factors,improved methods,engineering characteristics,and current field application status of the MICP.Additionally,it also explores the limitations and correspondingly proposes prospective applications via the MICP approach for soil improvement.This review indicates that the utilization of different environmental calcium-based wastes in MICP and combination of materials and MICP are conducive to meeting engineering and market demand.Furthermore,we recommend and encourage global collaborative study and practice with a view to commercializing MICP technique in the future.The current review purports to provide insights for engineers and interdisciplinary researchers,and guidance for future engineering applications.
基金Funded by the National Natural Science Foundation of China(No.51072035)the Ph D Program’s Foundation of Ministry of Education of China(No.20090092110029)+2 种基金the Research Innovation Program for College Graduates of Jiangsu Province(No.CXZZ_0145)the Scientific Research Foundation of Graduate School of Southeast University(Nos.YBJJ1127 and YBPY1208)the Ph D Program’s Foundation Funded by the Science and Technology Review(kjdb2011001)
文摘Loose sand particles could be cemented to sandstone by bio-cement（microbial induced magnesium carbonate）. The bio-sandstone was firstly prepared, and then the compressive strength and the porosity of the sandstone cemented by microbial induced magnesium carbonate were tested to characterize the cementation effectiveness. In addition, the formed mineral composition and the microstructure of bio-sandstone were analyzed by X-ray diffraction（XRD） and scanning electron microscopy（SEM）, respectively. The experimental results show that the feasibility of binding loose sand particles using microbial induced magnesium carbonate precipitation is available and the acquired compressive strength of bio-sandstone can be excellent at certain ages. Moreover, the compressive strength and the porosity could be improved with the increase of microbial induced magnesium carbonate content. XRD results indicate that the morphology of magnesium carbonate induced by microbe appears as needles and SEM results show that the cementation of loose sand particles to sandstone mainly relies on the microbial induced formation of magnesium carbonate precipitation around individual particles and at particle-particle contacts.
文摘Microbial-induced carbonate precipitation(MICP)and enzyme-induced carbonate precipitation(EICP)are two bio-cementation techniques,which are relatively new methods of ground improvement.While both techniques share some similarities,they can exhibit different overall behaviours due to the differences in urease enzyme sources and treatment methods.This paper presented 40 unconfined compressive strength(UCS)tests of MICP and EICP treated sand specimens with similar average calcium carbonate(CaCO3)content subjected to cycles of wetting-drying(WD),freezing-thawing(FT)and elevated temperature(fire resistance test e FR and thermogravimetric analysis e TG).The average CaCO3 content after a certain number of WD or FT cycles(ACn)and their corresponding UCS(qn)reduced while the mass loss increased.The EICP treated sand specimens appeared to exhibit a lower resistance to WD and FT cycles than MICP treated specimens possibly due to the presence of unbonded or loosely bonded CaCO3 within the soil matrix,which was subsequently removed during the wetting(during WD)or thawing(during FT)process.FR test and TG analysis showed a significant loss of mass and reduction in CaCO3 content with increased temperatures,possibly due to the thermal decomposition of CaCO3.A complete deterioration of the MICP and EICP treated sand specimens was observed for temperatures above 600C.The observed behaviours are complex and theoretical understanding is far behind to develop a constitutive model to predict qn.Therefore,a multi-objective evolutionary genetic algorithm(GA)that deals with pseudo-polynomial structures,known as evolutionary polynomial regression(EPR),was used to seek three choices from millions of polynomial models.The best EPR model produced an excellent prediction of qn with a minimum sum of squares error(SSE)of 2.392,mean squared error(MSE)of 0.075,root mean square error(RMSE)of 0.273 and a maximum coefficient of determination of 0.939.
基金supported by the UK Engineering and Physical Sciences Research Council(EPSRC)grant(reference number:EP/S02302X/1)for the University of Cambridge Centre for Doctoral Training in Future Infrastructure and Built Environment.
文摘Geotechnical research has been yearning for revolutionary innovations that could bring breakthroughs to conventional practices,especially at a time when energy efficiency and environmental sustainability are of unprecedented importance in the field.Recently,exciting opportunities emerged utilising microorganisms,the ubiquitous soil dwellers,to provide solutions to many geotechnical problems,prompting the development of the new,multidisciplinary subject of biogeotechnics.Research interest has been centred on the use of microbially induced carbonate precipitation(MICP)to improve the engineering properties of soils.The present work aims to comprehensively review the progress of more than a decade of research on the application of MICP in soil strengthening.Through elucidation of underlying mechanisms,compilation and interpretation of experimental findings,and in-depth discussion on pivotal aspects,with reference made to key published studies,a holistic picture of the state of the art of MICP-based soil strengthening is drawn.Current knowledge gaps are identified,and suggestions for future research are given,along with the opportunities and challenges that lie ahead of practically implementing this technique in real-world geotechnical applications.
基金support from National Research Foundation of Singapore under the Grant No.COT-V1-2020-4,and the support from JTC Corporation,Singapore.
文摘Soil liquefaction is a major geo-hazard.As liquefaction could occur anywhere in a sand layer and result in large-scale lateral spreading,treatment for liquefaction needs to be carried out over a large extent.The cost-effectiveness of the treatment then becomes a major consideration.With the development of microbial geotechnologies,some new approaches for liquefaction mitigation have been developed.Some of the methods offer more advantages over the existing methods.This paper gives an overview of the recent progress in bio related soil liquefaction mitigation methods.These include both bio-cementation and biogas desaturation.The mechanisms of bio-cementation and biogas desaturation are discussed.Recent up-scaled model tests and field trials are also reviewed.The studies so far have demonstrated that there is a great potential for some of liquefaction mitigation methods to be adopted in practice,although there are still challenges that need to be studied further.These include treatment efficiency,long-term sustainability,and biosafety.A brief introduction to some emerging technologies for liquefaction mitigation such as bio-gelation and use of fungi are also introduced.
基金Funded by the National Natural Science Foundation of China(No.51478290)the Key R&D Projects of Shanxi Province(No.201903D321113)。
文摘A new and more ecologically sound cementing material known as“bio-cement”has been found to have the capacity to consolidate loose gravel into sand columns offering a certain degree of strength,and to fill and repair cracks in concrete to restore resilience.The typical representative is the microbial induced calcium carbonate deposition technology(MICP)and enzyme induced calcite precipitation(EICP).As part of this research,EICP with soybean urease as the core was studied.The test results show that soybean urease activity is significantly affected by pH and urea concentration values,while the external nickel source is not found to impair a stimulating effect on activity.When the concrete specimens were immersed in the composite solution of soybean urease,urea,and calcium chloride after having been subjected to a high temperature,a continuous layer of white precipitations quickly appeared on the surface of the specimens.Measured using a metalloscope,the thickness of the precipitations was found to reach up to 2.0 mm,while the surface water absorption rate was reduced by 70%.The effects of this combined outcome are believed to significantly protect and improve the durability of the concrete specimens previously subjected to a high temperature.At the same time,the composite solution is shown to be capable of cementing fly ash,with the cubic strength of the finished samples reaching 4.0 MPa after 3 days.Results from the use of a scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and X-ray diffraction(XRD),reveal that both the white precipitations on the surface of the concrete specimens and the cement binding the fly ash particles are calcite crystals.It is concluded from these preliminary study results that the use of soybean urease as a bio-cement had proved successful.
