The biological stabilization of soil using microbially induced carbonate precipitation(MICP)employs ureolytic bacteria to precipitate calcium carbonate(CaCO3),which binds soil particles,enhancing strength,stiffness,an...The biological stabilization of soil using microbially induced carbonate precipitation(MICP)employs ureolytic bacteria to precipitate calcium carbonate(CaCO3),which binds soil particles,enhancing strength,stiffness,and erosion resistance.The unconfinedcompressive strength(UCS),a key measure of soil strength,is critical in geotechnical engineering as it directly reflectsthe mechanical stability of treated soils.This study integrates explainable artificialintelligence(XAI)with geotechnical insights to model the UCS of MICP-treated sands.Using 517 experimental data points and a combination of various input variables—including median grain size(D50),coefficientof uniformity(Cu),void ratio(e),urea concentration(Mu),calcium concentration(Mc),optical density(OD)of bacterial solution,pH,and total injection volume(Vt)—fivemachine learning(ML)models,including eXtreme gradient boosting(XGBoost),Light gradient boosting machine(LightGBM),random forest(RF),gene expression programming(GEP),and multivariate adaptive regression splines(MARS),were developed and optimized.The ensemble models(XGBoost,LightGBM,and RF)were optimized using the Chernobyl disaster optimizer(CDO),a recently developed metaheuristic algorithm.Of these,LightGBM-CDO achieved the highest accuracy for UCS prediction.XAI techniques like feature importance analysis(FIA),SHapley additive exPlanations(SHAP),and partial dependence plots(PDPs)were also used to investigate the complex non-linear relationships between the input and output variables.The results obtained have demonstrated that the XAI-driven models can enhance the predictive accuracy and interpretability of MICP processes,offering a sustainable pathway for optimizing geotechnical applications.展开更多
Discrete element method(DEM)-based numerical models in the YADE environment are used to simulate the constitutive response of uncemented and bio-cemented sands to investigate the influence of boundary conditions,loadi...Discrete element method(DEM)-based numerical models in the YADE environment are used to simulate the constitutive response of uncemented and bio-cemented sands to investigate the influence of boundary conditions,loading and testing conditions,and material types.Both the classical DEM model and the pore scale finite volume(PFV)-coupled DEM model are used to simulate the response of saturated uncemented and lightly cemented sands with a rigid wall boundary under both drained and undrained triaxial compression.A DEM model with flexible boundaries created using particle facet(PFacet)elements is used to simulate undrained triaxial compression of moderately cemented sands,including the influence of confining stress.The PFacet-based model is used to predict the transition from barreling failure to shear banding when the confining stress or the cementation degree increases.The classical DEM model with cohesive bonds of uniform strength is also used to successfully simulate the uniaxial compression response of a sand with an extremely high degree of cementation.Finally,this paper presents a particle-packing model consisting of multiple solid phases for cemented sands based on the understanding that not all particle types will have the same cohesive properties.This multiple solidphase model is a refinement of the classical DEM model that represents the particle physics more realistically,especially for heterogeneous systems.A preliminary parametric study is carried out considering varying cohesive properties and volume fractions for the different solid phases.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
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
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
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
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
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
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
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
Bio-mediated soil improvement methods keep on gaining the attention of geotechnical engineers and researchers globally due to their nature-based elegance and eco-friendliness.Most prevalent bio-mediated soil improveme...Bio-mediated soil improvement methods keep on gaining the attention of geotechnical engineers and researchers globally due to their nature-based elegance and eco-friendliness.Most prevalent bio-mediated soil improvement methods include microbially induced carbonate precipitation(MICP)and enzyme-induced carbonate precipitation(EICP).During their processes,the bacteria/free urease hydrolyzes the urea into ammonium and carbonic acid,which is accompanied by a considerable increase of alkalinity(about pH 9.0).The major problem associated with the above techniques is the release of gaseous ammonia that is extremely detrimental.Therefore,this study aims to propose a new sustainable approach involving lactic acid bacteria to facilitate the calcium phosphate mineralization for the strengthening of sand matrix.The major objectives of this investigation are:(i)to evaluate the urease activity of the lactic acid bacteria under different temperatures,pH conditions and additions of metal ions,(ii)to assess the treated sand matrix,(iii)to perform cost analysis.The outcomes indicated that Limosilactobacillus sp.could effectively facilitate the urea hydrolysis,hence increasing the pH from acidic to neutral and providing a desirable environment for the calcium phosphate to mineralize within the voids of the sand.The addition of 0.01%Ni^(2+)in culture media was found to enhance the urease activity by 38.8%and compressive strength over 40%.A combined formation of amorphous-and whisker-like precipitates could bridge a larger area at particle-particle contact points,thereby faciliating a strong force-network in sand matrix.The mineralized calcium phosphate compound was found to be brushite.The cost herein for producing 1 L treatment solution was estimated to be about 2.5-folds and 11.8-folds lower compared to that of MICP and EICP treatment solutions,respectively.Moreover,since the treatment pH could potentially be regulated between acidic-neural range,it would greatly control the release of gaseous ammonia.With several environmental and economical benefits,the study has disclosed a new sustainable direction for sand improvement via the use of lactic acid bacteria.展开更多
文摘The biological stabilization of soil using microbially induced carbonate precipitation(MICP)employs ureolytic bacteria to precipitate calcium carbonate(CaCO3),which binds soil particles,enhancing strength,stiffness,and erosion resistance.The unconfinedcompressive strength(UCS),a key measure of soil strength,is critical in geotechnical engineering as it directly reflectsthe mechanical stability of treated soils.This study integrates explainable artificialintelligence(XAI)with geotechnical insights to model the UCS of MICP-treated sands.Using 517 experimental data points and a combination of various input variables—including median grain size(D50),coefficientof uniformity(Cu),void ratio(e),urea concentration(Mu),calcium concentration(Mc),optical density(OD)of bacterial solution,pH,and total injection volume(Vt)—fivemachine learning(ML)models,including eXtreme gradient boosting(XGBoost),Light gradient boosting machine(LightGBM),random forest(RF),gene expression programming(GEP),and multivariate adaptive regression splines(MARS),were developed and optimized.The ensemble models(XGBoost,LightGBM,and RF)were optimized using the Chernobyl disaster optimizer(CDO),a recently developed metaheuristic algorithm.Of these,LightGBM-CDO achieved the highest accuracy for UCS prediction.XAI techniques like feature importance analysis(FIA),SHapley additive exPlanations(SHAP),and partial dependence plots(PDPs)were also used to investigate the complex non-linear relationships between the input and output variables.The results obtained have demonstrated that the XAI-driven models can enhance the predictive accuracy and interpretability of MICP processes,offering a sustainable pathway for optimizing geotechnical applications.
基金support for this study from National Science Foundation(NSF)under the Engineering Research Centers(ERC)program,grant EEC-1449501.
文摘Discrete element method(DEM)-based numerical models in the YADE environment are used to simulate the constitutive response of uncemented and bio-cemented sands to investigate the influence of boundary conditions,loading and testing conditions,and material types.Both the classical DEM model and the pore scale finite volume(PFV)-coupled DEM model are used to simulate the response of saturated uncemented and lightly cemented sands with a rigid wall boundary under both drained and undrained triaxial compression.A DEM model with flexible boundaries created using particle facet(PFacet)elements is used to simulate undrained triaxial compression of moderately cemented sands,including the influence of confining stress.The PFacet-based model is used to predict the transition from barreling failure to shear banding when the confining stress or the cementation degree increases.The classical DEM model with cohesive bonds of uniform strength is also used to successfully simulate the uniaxial compression response of a sand with an extremely high degree of cementation.Finally,this paper presents a particle-packing model consisting of multiple solid phases for cemented sands based on the understanding that not all particle types will have the same cohesive properties.This multiple solidphase model is a refinement of the classical DEM model that represents the particle physics more realistically,especially for heterogeneous systems.A preliminary parametric study is carried out considering varying cohesive properties and volume fractions for the different solid phases.
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.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.
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supported by the Japan Society for the Promotion of Science(JSPS)KAKENHI Grant Number JP22H01581the authors sincerely acknowledge the support.
文摘Bio-mediated soil improvement methods keep on gaining the attention of geotechnical engineers and researchers globally due to their nature-based elegance and eco-friendliness.Most prevalent bio-mediated soil improvement methods include microbially induced carbonate precipitation(MICP)and enzyme-induced carbonate precipitation(EICP).During their processes,the bacteria/free urease hydrolyzes the urea into ammonium and carbonic acid,which is accompanied by a considerable increase of alkalinity(about pH 9.0).The major problem associated with the above techniques is the release of gaseous ammonia that is extremely detrimental.Therefore,this study aims to propose a new sustainable approach involving lactic acid bacteria to facilitate the calcium phosphate mineralization for the strengthening of sand matrix.The major objectives of this investigation are:(i)to evaluate the urease activity of the lactic acid bacteria under different temperatures,pH conditions and additions of metal ions,(ii)to assess the treated sand matrix,(iii)to perform cost analysis.The outcomes indicated that Limosilactobacillus sp.could effectively facilitate the urea hydrolysis,hence increasing the pH from acidic to neutral and providing a desirable environment for the calcium phosphate to mineralize within the voids of the sand.The addition of 0.01%Ni^(2+)in culture media was found to enhance the urease activity by 38.8%and compressive strength over 40%.A combined formation of amorphous-and whisker-like precipitates could bridge a larger area at particle-particle contact points,thereby faciliating a strong force-network in sand matrix.The mineralized calcium phosphate compound was found to be brushite.The cost herein for producing 1 L treatment solution was estimated to be about 2.5-folds and 11.8-folds lower compared to that of MICP and EICP treatment solutions,respectively.Moreover,since the treatment pH could potentially be regulated between acidic-neural range,it would greatly control the release of gaseous ammonia.With several environmental and economical benefits,the study has disclosed a new sustainable direction for sand improvement via the use of lactic acid bacteria.
