The biocemented coral sand pile composite foundation represents an innovative foundation improvement technology,utilizing Microbially Induced Carbonate Precipitation(MICP)to consolidate a specific volume of coral sand...The biocemented coral sand pile composite foundation represents an innovative foundation improvement technology,utilizing Microbially Induced Carbonate Precipitation(MICP)to consolidate a specific volume of coral sand within the foundation into piles with defined strength,thereby enabling them to collaboratively bear external loads with the surrounding unconsolidated coral sand.In this study,a series of shaking table model tests were conducted to explore the dynamic response of the biocemented coral sand pile composite foundation under varying seismic wave types and peak accelerations.The surface macroscopic phenomena,excess pore water pressure ratio,acceleration response,and vertical settlement were measured and analysed in detail.Test results show that seismic wave types play a decisive role in the macroscopic surface phenomena and the response of the excess pore water pressure ratio.The cumulative settlement of the upper structure under the action of Taft waves was about 1.5 times that of El Centro waves and Kobe waves.The most pronounced liquefaction phenomena were recorded under the Taft wave,followed by the El Centro wave,and subsequently the Kobe wave.An observed positive correlation was established between the liquefaction phenomenon and the Aristotelian in-tensity of the seismic waves.However,variations in seismic wave types exerted minimal influence on the ac-celeration amplification factor of the coral sand foundation.Analysis of the acceleration amplification factor revealed a triphasic pattern-initially increasing,subsequently decreasing,and finally increasing again-as burial depth increased,in relation to the peak value of the input acceleration.This study confirms that the biocemented coral sand pile composite foundation can effectively enhance the liquefaction resistance of coral sand foundations..展开更多
It is difficult to collect and characterise well-preserved samples of weakly-cemented granular rocks as conventional sampling techniques often result in destruction of the cementation.An alternative approach is to pre...It is difficult to collect and characterise well-preserved samples of weakly-cemented granular rocks as conventional sampling techniques often result in destruction of the cementation.An alternative approach is to prepare synthetic geomaterials to match required specifications.This paper introduces microbially induced carbonate precipitation(MICP)as a method to reliably deliver artificiallycemented specimens with customised properties,closely resembling those of soft carbonate sandstones.The specimens are generated from materials with two highly different particle size distributions(PSDs)to access a range of achievable combinations of strengths and porosities.The MICP parameters are kept constant across all samples to obtain similar calcium carbonate characteristics(size of individual crystals,type,etc.),while injected volume is varied to achieve different cementation levels.Although uniform cementation of very coarse sands has been considered very difficult to achieve,the results show that both the fine and coarse sand specimens present high degrees of uniformity and a good degree of repeatability.The unconfined compressive strengths(UCSs)(less than 3000 kPa)and porosities(0.25e0.4)of the artificial specimens fall in the same range of values reported for natural rocks.The strength gainwas greater in the fine sand than that in the coarse sand,as the void size in the latter was significantly larger compared to the calcium carbonate crystals’size,resulting in precipitation on less effective locations,away from contacts between particles.The strengths and porosities obtained for the two sands in this work fall within ranges reported in the literature for natural soft rocks,demonstrating theMICP technique is able to achieve realistic properties and may be used to produce a full range of properties by varying the grain sizes,and possibly the width of PSD.展开更多
Because of the high cost of cultivating urease-producing bacteria(UPB),this paper proposes soybean-urease-induced carbonate precipitation(SUICP)as a novel biocement for treatment of nickel contaminants and cementation...Because of the high cost of cultivating urease-producing bacteria(UPB),this paper proposes soybean-urease-induced carbonate precipitation(SUICP)as a novel biocement for treatment of nickel contaminants and cementation of sandy soil.We found the optimal soaking time and soybean-powder content to be 30 min and 130 g/L,respectively,based on a standard of 5 U of urease activity.The most efficient removal of nickel ions is obtained with an ideal mass ratio of urea to nickel ions to soybean-powder filtrate(SPF)of 1:2.4:20.The removal efficiency of nickel ions can reach 89.42%when treating 1 L of nickel-ion solution(1200 mg/L with the optimal mass ratio).In incinerated bottom ash(IBA),the removal efficiency of nickel ions is 99.33%with the optimal mass ratio.In biocemented sandy soil,the average unconfined compressive strength(UCS)of sand blocks cemented with soybean urease-based biocement can reach 118.89 kPa when the cementation level is 3.Currently,the average content of CaCO_(3)in sand blocks is 2.52%.As a result,the SUICP process can be applied to remove heavy metal ions in wastewater or solid waste and improve the mechanical properties of soft soil foundations.展开更多
Microbially or enzyme induced carbonate precipitation has emerged to be a new type of soil improvement method.However,it appears that the biocementation process is affected by many factors and a common understanding o...Microbially or enzyme induced carbonate precipitation has emerged to be a new type of soil improvement method.However,it appears that the biocementation process is affected by many factors and a common understanding on the control factors on the biocement effect has not been reached.This paper attempts to identify the main factors that controlling the MICP or EICP effect through an in-depth discussion on the fundamentals of biocementation process.Similar to other cemented granular materials,biocemented soil is a structural soil composite consisting of soil skeleton and biocement force chain or biocement network.The strength and stiffness of the biocemented soil is controlled by the reinforcement effect of the biocement network on the soil skeleton or the interplay of the soil skeleton and precipitates.The contribution of the strength by soil skeleton is affected by the soil types and soil properties,while the contribution of the precipitates is through the distribution of the biocement network and the properties of the precipitates.展开更多
Microbially induced carbonate precipitation(MICP)is a promising technique to enhance the geotechnical properties of geomaterial either by strengthening via biocementation or reducing the hydraulic conductivity via bio...Microbially induced carbonate precipitation(MICP)is a promising technique to enhance the geotechnical properties of geomaterial either by strengthening via biocementation or reducing the hydraulic conductivity via bioclogging.This rate of modification mainly depends on the amount,and nature of biomineral pre-cipitated and it is influenced by various environmental,chemical,and microbial factors.Given this,the present study aims to investigate the effect of biochemical conditions such as concentration of biomass and chemical reagents on the amount and nature of biomineral and its impact on the strength and permeability of biomodified sand.For this,the two microbes i.e.,Sporosarcina pasteuri and isolated Proteus species at three different initial concentrations and chemical reagents by varying 0.1-1 molar of urea and calcium were considered.The amount and microstructural behavior of biomineral in different biochemical conditions concluded that the governing mechanism differs for both biocementation and bioclogging under identical MICP treatment.The strength enhancement or biocementation is dependent on the size of the biomineral precipitated whereas the reduction in permeability or bioclogging is mainly dominated by the amount of biomineral.The optimum value of biochemical conditions i.e.,1o°cells/ml of biomass and 0.25 M con-centration of cementation reagents was chosen to further evaluate the effect of equal MICP treatment on the biocementation and bioclogging of sands having different grain sizes.The study infers that not the absolute size of the biomineral but the relative size of soil grain and biomineral influence the linkage between the soil particles and hence affect the strength of biomodified soil.展开更多
Biocementation-based soil improvement is an emerging ground treatment method in geotechnical engineering that has garnered extensive attention over the past two decades.One of the challenges associated with this metho...Biocementation-based soil improvement is an emerging ground treatment method in geotechnical engineering that has garnered extensive attention over the past two decades.One of the challenges associated with this method revolves around the uniformity of biocementation,a crucial factor closely tied to bio-grouting technology.The traditional biotreatment methods,the two-phase method and the one-phase method,suffer from the issue of non-uniform biocementation.Consequently,in recent years,various improved grouting technologies have been proposed to address this concern by aiding bacterial adsorption and controlling carbonate precipitation.This paper reviews the mechanisms and grouting processes employed in these enhanced bio-grouting technologies.Additionally,the challenges of implementing these grouting technologies in real-world applications are also thoroughly discussed.展开更多
Reasonable control of rainwater infiltration rate can ensure that soil slope will not fail due to rapid infiltration of rainwater in heavy rainfall,and at the same time,more rainwater can be infiltrated in light rainf...Reasonable control of rainwater infiltration rate can ensure that soil slope will not fail due to rapid infiltration of rainwater in heavy rainfall,and at the same time,more rainwater can be infiltrated in light rainfall to meet the water demand of animals and plants.In this study,based on microbial-induced calcium carbonate precipitation(MICP)technique,a controllable bio-method for rainfall infiltration of soil slope was proposed.To have a comprehensive understanding the relationship among the rainwater infiltration control capacity,biocement treated soil permeability,slope angle and rainfall intensity,a series of physical modelling experiments of rainfall diversion on slopes with three types of soils and three slope angles were carried out in the presence of various rainfall intensities.Experimental results indicated that the proposed bio-method had the ability of controlling rainwater infiltration in term of varying rounds of biocement spraying treatment.In general,it was found that the rainwater infiltration decreases with the increase in slope angle and rainfall intensity.In the worst case of smallest slope angle(15°)and lightest rainfall intensity(n=50 mm/h),more than 82.6%,92.2%and 84.4%of rainwater were prevented from infiltration into the MICP treated natural sand,fine sand and medium sand,respectively,while the untreated soils were not able to prevent the rainwater infiltration at all.The corre-sponding maximum local uniaxial compressive strength for the MICP treated natural sand,fine sand and medium sand,respectively,were found to be 2.3 MPa,2.0 MPa,2.6 MPa,whereas the flexural stresses were 0.46 MPa,0.33 MPa,0.67 MPa,which could resist rainfall droplet impact force.Overall,the proposed bio-method showed good rainwater infiltration control capacity and high bearing strength against the impact of heavy rainfalls,suggesting a good potential to mitigate the rainfall-induced landslides.展开更多
This paper presents a microdevice developed to measure the electrical conductivity of a liquid or a saturated porous medium using Wenner method.It is developed in the context of biocementation as soil improvement tech...This paper presents a microdevice developed to measure the electrical conductivity of a liquid or a saturated porous medium using Wenner method.It is developed in the context of biocementation as soil improvement technique,which is used in Civil Engineering applications to produce calcium carbonate through bacterial or enzymatic activity,replacing the use of other binder materials such as cement or resins,and therefore reducing carbon footprint.The microdevice was used to measure urease activity in the soil interstitial fluid,to investigate if bacterial activity could be affected by the presence of the particles and tortuosity from pore geometry.Such analysis is important to understand biocementation mechanism inside the soil and helps to improve the design of such treatment solutions.The device is basically a squared reservoir printed in polypropylene using a 3D printing machine,incorporating stainless steel electrodes in its base.The electrical resistivity was computed adopting Wenner method,by connecting 4 PCB electrodes to a signal generator and an oscilloscope for measuring the voltage when a AC current of 1 mA was applied.Both square and sinusoidal waves with 5 kHz frequency were selected among other frequencies.The measurements were adjusted during the calibration of the microdevice,done using standard salt solutions with known electrical conductivity measured using an electrical conductivity probe.For the bacterial activity measurements,the bacterial and urea solutions were added to a uniform-graded size quarzitic sand(average diameter 0.3 mm)placed inside the microdevice and covering completely the electrodes.Bacterial activity was not affected by the presence of the sand,which confirms that this treatment is effective for this type of soils.展开更多
Bacterial suspension is an essential component of microbially induced carbonate precipitation(MICP)-based biocement and a large-scale production is required for field applications.In this study,a new bacterial concent...Bacterial suspension is an essential component of microbially induced carbonate precipitation(MICP)-based biocement and a large-scale production is required for field applications.In this study,a new bacterial concentration method is proposed to enable high concentration bacterial suspension to be produced to facilitate field work.By adding low concentration calcium to bacterial suspension,flocs are formed and bacterial cells are adsorbed on the flocs to achieve bacterial concentration.Compared to the traditional bacterial concentration method using centrifugation and freezing-drying method,the proposed method can concentrate a large volume of bacterial suspension without using special equipment.The feasibility of this method is verified by bacterial concentration tests,solution tests and sand column treatment tests.The results of both the solution test and the sand column treatment test show that the bacterial suspension concentrated by the proposed method can be effectively used for soil biocementation.There is a threshold calcium concentration that allows a complete bacterial concentration for the proposed method,and this threshold calcium concentration tends to increase linearly with the optical density of the cell suspension at a wavelength of 600 nm(OD_(600)).展开更多
基金supported by the National Natural Science Foundation of China(No.51978103,No.52308340,No.52408355)the Postdoctoral Fellowship Program of CPSF(No.BX20240450)Chongqing Talent Innovation and Entrepreneurship Demonstration Team Project(No.cstc2024ycjh-bgzxm0012).
文摘The biocemented coral sand pile composite foundation represents an innovative foundation improvement technology,utilizing Microbially Induced Carbonate Precipitation(MICP)to consolidate a specific volume of coral sand within the foundation into piles with defined strength,thereby enabling them to collaboratively bear external loads with the surrounding unconsolidated coral sand.In this study,a series of shaking table model tests were conducted to explore the dynamic response of the biocemented coral sand pile composite foundation under varying seismic wave types and peak accelerations.The surface macroscopic phenomena,excess pore water pressure ratio,acceleration response,and vertical settlement were measured and analysed in detail.Test results show that seismic wave types play a decisive role in the macroscopic surface phenomena and the response of the excess pore water pressure ratio.The cumulative settlement of the upper structure under the action of Taft waves was about 1.5 times that of El Centro waves and Kobe waves.The most pronounced liquefaction phenomena were recorded under the Taft wave,followed by the El Centro wave,and subsequently the Kobe wave.An observed positive correlation was established between the liquefaction phenomenon and the Aristotelian in-tensity of the seismic waves.However,variations in seismic wave types exerted minimal influence on the ac-celeration amplification factor of the coral sand foundation.Analysis of the acceleration amplification factor revealed a triphasic pattern-initially increasing,subsequently decreasing,and finally increasing again-as burial depth increased,in relation to the peak value of the input acceleration.This study confirms that the biocemented coral sand pile composite foundation can effectively enhance the liquefaction resistance of coral sand foundations..
文摘It is difficult to collect and characterise well-preserved samples of weakly-cemented granular rocks as conventional sampling techniques often result in destruction of the cementation.An alternative approach is to prepare synthetic geomaterials to match required specifications.This paper introduces microbially induced carbonate precipitation(MICP)as a method to reliably deliver artificiallycemented specimens with customised properties,closely resembling those of soft carbonate sandstones.The specimens are generated from materials with two highly different particle size distributions(PSDs)to access a range of achievable combinations of strengths and porosities.The MICP parameters are kept constant across all samples to obtain similar calcium carbonate characteristics(size of individual crystals,type,etc.),while injected volume is varied to achieve different cementation levels.Although uniform cementation of very coarse sands has been considered very difficult to achieve,the results show that both the fine and coarse sand specimens present high degrees of uniformity and a good degree of repeatability.The unconfined compressive strengths(UCSs)(less than 3000 kPa)and porosities(0.25e0.4)of the artificial specimens fall in the same range of values reported for natural rocks.The strength gainwas greater in the fine sand than that in the coarse sand,as the void size in the latter was significantly larger compared to the calcium carbonate crystals’size,resulting in precipitation on less effective locations,away from contacts between particles.The strengths and porosities obtained for the two sands in this work fall within ranges reported in the literature for natural soft rocks,demonstrating theMICP technique is able to achieve realistic properties and may be used to produce a full range of properties by varying the grain sizes,and possibly the width of PSD.
基金supported by the Opening Funds of Jiangsu Key Laboratory of Construction Materials(No.CM2018-02)the Key Project of Natural Science Foundation of Zhejiang Province,China(No.LZ22E080003)the General Project of Natural Science Foundation of Zhejiang Province,China(No.LY20E080002).
文摘Because of the high cost of cultivating urease-producing bacteria(UPB),this paper proposes soybean-urease-induced carbonate precipitation(SUICP)as a novel biocement for treatment of nickel contaminants and cementation of sandy soil.We found the optimal soaking time and soybean-powder content to be 30 min and 130 g/L,respectively,based on a standard of 5 U of urease activity.The most efficient removal of nickel ions is obtained with an ideal mass ratio of urea to nickel ions to soybean-powder filtrate(SPF)of 1:2.4:20.The removal efficiency of nickel ions can reach 89.42%when treating 1 L of nickel-ion solution(1200 mg/L with the optimal mass ratio).In incinerated bottom ash(IBA),the removal efficiency of nickel ions is 99.33%with the optimal mass ratio.In biocemented sandy soil,the average unconfined compressive strength(UCS)of sand blocks cemented with soybean urease-based biocement can reach 118.89 kPa when the cementation level is 3.Currently,the average content of CaCO_(3)in sand blocks is 2.52%.As a result,the SUICP process can be applied to remove heavy metal ions in wastewater or solid waste and improve the mechanical properties of soft soil foundations.
基金support by the National Natural Science Foundation of China(NSFC)(Grant Nos.52178319,52108307,51708243)the Natural Science Foundation of Fujian Province,China(Grant Nos.2022J05020,2022J05127).
文摘Microbially or enzyme induced carbonate precipitation has emerged to be a new type of soil improvement method.However,it appears that the biocementation process is affected by many factors and a common understanding on the control factors on the biocement effect has not been reached.This paper attempts to identify the main factors that controlling the MICP or EICP effect through an in-depth discussion on the fundamentals of biocementation process.Similar to other cemented granular materials,biocemented soil is a structural soil composite consisting of soil skeleton and biocement force chain or biocement network.The strength and stiffness of the biocemented soil is controlled by the reinforcement effect of the biocement network on the soil skeleton or the interplay of the soil skeleton and precipitates.The contribution of the strength by soil skeleton is affected by the soil types and soil properties,while the contribution of the precipitates is through the distribution of the biocement network and the properties of the precipitates.
文摘Microbially induced carbonate precipitation(MICP)is a promising technique to enhance the geotechnical properties of geomaterial either by strengthening via biocementation or reducing the hydraulic conductivity via bioclogging.This rate of modification mainly depends on the amount,and nature of biomineral pre-cipitated and it is influenced by various environmental,chemical,and microbial factors.Given this,the present study aims to investigate the effect of biochemical conditions such as concentration of biomass and chemical reagents on the amount and nature of biomineral and its impact on the strength and permeability of biomodified sand.For this,the two microbes i.e.,Sporosarcina pasteuri and isolated Proteus species at three different initial concentrations and chemical reagents by varying 0.1-1 molar of urea and calcium were considered.The amount and microstructural behavior of biomineral in different biochemical conditions concluded that the governing mechanism differs for both biocementation and bioclogging under identical MICP treatment.The strength enhancement or biocementation is dependent on the size of the biomineral precipitated whereas the reduction in permeability or bioclogging is mainly dominated by the amount of biomineral.The optimum value of biochemical conditions i.e.,1o°cells/ml of biomass and 0.25 M con-centration of cementation reagents was chosen to further evaluate the effect of equal MICP treatment on the biocementation and bioclogging of sands having different grain sizes.The study infers that not the absolute size of the biomineral but the relative size of soil grain and biomineral influence the linkage between the soil particles and hence affect the strength of biomodified soil.
基金support by the National Natural Science Foundation of China(NSFC)(Grant Nos.52178319,52108307,52078236,51878313,51708243)the Natural Science Foundation of Fujian Province,China(Grant Nos.2022J05020,2022J05127).
文摘Biocementation-based soil improvement is an emerging ground treatment method in geotechnical engineering that has garnered extensive attention over the past two decades.One of the challenges associated with this method revolves around the uniformity of biocementation,a crucial factor closely tied to bio-grouting technology.The traditional biotreatment methods,the two-phase method and the one-phase method,suffer from the issue of non-uniform biocementation.Consequently,in recent years,various improved grouting technologies have been proposed to address this concern by aiding bacterial adsorption and controlling carbonate precipitation.This paper reviews the mechanisms and grouting processes employed in these enhanced bio-grouting technologies.Additionally,the challenges of implementing these grouting technologies in real-world applications are also thoroughly discussed.
基金supports from the Ministry of National Development,Singapore(No.SUL2013-1)the National Research Foundation of Singapore(L2NICCFP2-2015-1)are gratefully acknowledged.
文摘Reasonable control of rainwater infiltration rate can ensure that soil slope will not fail due to rapid infiltration of rainwater in heavy rainfall,and at the same time,more rainwater can be infiltrated in light rainfall to meet the water demand of animals and plants.In this study,based on microbial-induced calcium carbonate precipitation(MICP)technique,a controllable bio-method for rainfall infiltration of soil slope was proposed.To have a comprehensive understanding the relationship among the rainwater infiltration control capacity,biocement treated soil permeability,slope angle and rainfall intensity,a series of physical modelling experiments of rainfall diversion on slopes with three types of soils and three slope angles were carried out in the presence of various rainfall intensities.Experimental results indicated that the proposed bio-method had the ability of controlling rainwater infiltration in term of varying rounds of biocement spraying treatment.In general,it was found that the rainwater infiltration decreases with the increase in slope angle and rainfall intensity.In the worst case of smallest slope angle(15°)and lightest rainfall intensity(n=50 mm/h),more than 82.6%,92.2%and 84.4%of rainwater were prevented from infiltration into the MICP treated natural sand,fine sand and medium sand,respectively,while the untreated soils were not able to prevent the rainwater infiltration at all.The corre-sponding maximum local uniaxial compressive strength for the MICP treated natural sand,fine sand and medium sand,respectively,were found to be 2.3 MPa,2.0 MPa,2.6 MPa,whereas the flexural stresses were 0.46 MPa,0.33 MPa,0.67 MPa,which could resist rainfall droplet impact force.Overall,the proposed bio-method showed good rainwater infiltration control capacity and high bearing strength against the impact of heavy rainfalls,suggesting a good potential to mitigate the rainfall-induced landslides.
基金FCT I.P,for the funding through CALCITE Project(ref.PTDC/ECI-EGC/1086/2021).
文摘This paper presents a microdevice developed to measure the electrical conductivity of a liquid or a saturated porous medium using Wenner method.It is developed in the context of biocementation as soil improvement technique,which is used in Civil Engineering applications to produce calcium carbonate through bacterial or enzymatic activity,replacing the use of other binder materials such as cement or resins,and therefore reducing carbon footprint.The microdevice was used to measure urease activity in the soil interstitial fluid,to investigate if bacterial activity could be affected by the presence of the particles and tortuosity from pore geometry.Such analysis is important to understand biocementation mechanism inside the soil and helps to improve the design of such treatment solutions.The device is basically a squared reservoir printed in polypropylene using a 3D printing machine,incorporating stainless steel electrodes in its base.The electrical resistivity was computed adopting Wenner method,by connecting 4 PCB electrodes to a signal generator and an oscilloscope for measuring the voltage when a AC current of 1 mA was applied.Both square and sinusoidal waves with 5 kHz frequency were selected among other frequencies.The measurements were adjusted during the calibration of the microdevice,done using standard salt solutions with known electrical conductivity measured using an electrical conductivity probe.For the bacterial activity measurements,the bacterial and urea solutions were added to a uniform-graded size quarzitic sand(average diameter 0.3 mm)placed inside the microdevice and covering completely the electrodes.Bacterial activity was not affected by the presence of the sand,which confirms that this treatment is effective for this type of soils.
基金supports by the National Natural Science Foundation of China(Grant Nos.52108307 and 52178319)the National Natural Science Foundation of Fujian Province,China(Grant No.2022J05020).
文摘Bacterial suspension is an essential component of microbially induced carbonate precipitation(MICP)-based biocement and a large-scale production is required for field applications.In this study,a new bacterial concentration method is proposed to enable high concentration bacterial suspension to be produced to facilitate field work.By adding low concentration calcium to bacterial suspension,flocs are formed and bacterial cells are adsorbed on the flocs to achieve bacterial concentration.Compared to the traditional bacterial concentration method using centrifugation and freezing-drying method,the proposed method can concentrate a large volume of bacterial suspension without using special equipment.The feasibility of this method is verified by bacterial concentration tests,solution tests and sand column treatment tests.The results of both the solution test and the sand column treatment test show that the bacterial suspension concentrated by the proposed method can be effectively used for soil biocementation.There is a threshold calcium concentration that allows a complete bacterial concentration for the proposed method,and this threshold calcium concentration tends to increase linearly with the optical density of the cell suspension at a wavelength of 600 nm(OD_(600)).
