Effect of drying-wetting cycles on pore characteristics and mechanical properties of enzyme-induced carbonate precipitation-reinforced sea sand

Enzyme-induced carbonate precipitation(EICP)is an emanating,eco-friendly and potentially sound technique that has presented promise in various geotechnical applications.However,the durability and microscopic characteristics of EICP-treated specimens against the impact of drying-wetting(D-W)cycles is under-explored yet.This study investigates the evolution of mechanical behavior and pore charac-teristics of EICP-treated sea sand subjected to D-W cycles.The uniaxial compressive strength(UCS)tests,synchrotron radiation micro-computed tomography(micro-CT),and three-dimensional(3D)recon-struction of CT images were performed to study the multiscale evolution characteristics of EICP-reinforced sea sand under the effect of D-W cycles.The potential correlations between microstructure characteristics and macro-mechanical property deterioration were investigated using gray relational analysis(GRA).Results showed that the UCS of EICP-treated specimens decreases by 63.7% after 15 D-W cycles.The proportion of mesopores gradually decreases whereas the proportion of macropores in-creases due to the exfoliated calcium carbonate with increasing number of D-W cycles.The micro-structure in EICP-reinforced sea sand was gradually disintegrated,resulting in increasing pore size and development of pore shape from ellipsoidal to columnar and branched.The gray relational degree suggested that the weight loss rate and UCS deterioration were attributed to the development of branched pores with a size of 100-1000 m m under the action of D-W cycles.Overall,the results in this study provide a useful guidancee for the long-term stability and evolution characteristics of EICP-reinforced sea sand under D-W weathering conditions.

Coupled multiphysical model for investigation of influence factors in the application of microbially induced calcite precipitation

The study presents a comprehensive coupled thermo-bio-chemo-hydraulic(T-BCH)modeling framework for stabilizing soils using microbially induced calcite precipitation(MICP).The numerical model considers relevant multiphysics involved in MICP,such as bacterial ureolytic activities,biochemical reactions,multiphase and multicomponent transport,and alteration of the porosity and permeability.The model incorporates multiphysical coupling effects through well-established constitutive relations that connect parameters and variables from different physical fields.It was implemented in the open-source finite element code OpenGeoSys(OGS),and a semi-staggered solution strategy was designed to solve the couplings,allowing for flexible model settings.Therefore,the developed model can be easily adapted to simulate MICP applications in different scenarios.The numerical model was employed to analyze the effect of various factors,including temperature,injection strategies,and application scales.Besides,a TBCH modeling study was conducted on the laboratory-scale domain to analyze the effects of temperature on urease activity and precipitated calcium carbonate.To understand the scale dependency of MICP treatment,a large-scale heterogeneous domain was subjected to variable biochemical injection strategies.The simulations conducted at the field-scale guided the selection of an injection strategy to achieve the desired type and amount of precipitation.Additionally,the study emphasized the potential of numerical models as reliable tools for optimizing future developments in field-scale MICP treatment.The present study demonstrates the potential of this numerical framework for designing and optimizing the MICP applications in laboratory-,prototype-,and field-scale scenarios.

Field implementation of enzyme-induced carbonate precipitation technology for reinforcing a bedding layer beneath an underground cable duct

A suitable bearing capacity of foundation is critical for the safety of civil structures.Sometimes foundation reinforcement is necessary and an effective and environmentally friendly method would be the preferred choice.In this study,the potential application of enzyme-induced carbonate precipitation(EICP)was investigated for reinforcing a 0.6 m bedding layer on top of clay to improve the bearing capacity of the foundation underneath an underground cable duct.Laboratory experiments were conducted to determine the optimal operational parameters for the extraction of crude urease liquid and optimal grain size range of sea sands to be used to construct the bedding layer.Field tests were planned based on orthogonal experimental design to study the factors that would significantly affect the biocementation effect on site.The dynamic deformation modulus,calcium carbonate content and longterm ground stress variations were used to evaluate the bio-cementation effect and the long-term performance of the EICP-treated bedding layer.The laboratory test results showed that the optimal duration for the extraction of crude urease liquid is 1 h and the optimal usage of soybean husk powder in urease extraction solution is 100 g/L.The calcium carbonate production rate decreases significantly when the concentration of cementation solution exceeds 0.5 mol/L.The results of site trial showed that the number of EICP treatments has the most significant impact on the effectiveness of EICP treatment and the highest dynamic deformation modulus(Evd)of EICP-treated bedding layer reached 50.55 MPa.The area with better bio-cementation effect was found to take higher ground stress which validates that the EICP treatment could improve the bearing capacity of foundation by reinforcing the bedding layer.The field trial described and the analysis introduced in this paper can provide a practical basis for applying EICP technology to the reinforcement of bedding layer in poor ground conditions.

Garlic extract addition for soil improvement at various temperatures using enzyme-induced carbonate precipitation (EICP) method

Enzyme-induced carbonate precipitation (EICP) is an emerging technique to improve the soil and most studies are carried out at room temperature. However, considering some foundations are in high-temperature environments (>40 ℃), the higher urease activity at high temperature results in the solidification inhomogeneity, limiting the application of EICP. The higher urease activity at high temperature hampers the application of EICP because of solidification inhomogeneity. The garlic extract has been used as a type of urease inhibitor in medical science and food engineering. Here, we propose to use it to control urease activity for sand solidification at high temperature. The effects of garlic extract addition on urease activity and precipitation rates for calcium carbonate (CaCO_(3)) were studied. Extra tests were conducted to study the effect of garlic extract addition on the solidification homogeneity. The results showed that the garlic extract addition significantly decreased urease activity. To reduce the rate of CaCO3 precipitation at different temperatures, a suitable concentration of garlic extract was necessary to obtain a suitable urease activity. In the sand solidification test, garlic extract addition resulted in a smaller difference in sonic time values or CaCO_(3) contents at different parts of samples. The improved solidification homogeneity can achieve higher strength. The correlation between sonic time values and CaCO_(3) content was higher than that between CaCO3 content and strength. Appropriate concentrations of garlic extract were obtained at 35 ℃, 40℃, 45 ℃, 50 ℃, and 55 ℃. The proposed garlic extract addition method was significant to improve the homogeneity of solidified soil in practical engineering applications.

The Reduction of the Permeability of a Lateritic Soil through the Application of Microbially Induced Calcite Precipitation

Lateritic soils are frequently utilised in tropical areas of the developing world as an engineering material in the construction of rural earth roads, usually in the form of engineered natural surface (ENS) roads. The heavy, seasonal rainfalls common to the tropics results in ENS roads becoming quickly saturated with rainwater, and no longer accessible to motorised transportation. Microbially induced calcite precipitation (MICP) has been successfully used as a treatment process to decrease the permeability of clean, cohesionless sands by studies trying to impede the movement of groundwater, and any pollutants they may contain. In order to see if MICP treatment can also reduce the susceptibility of ENS road lateritic soils to rainwater saturation, this study has treated a Brazilian sample extracted from an ENS road in Espirito do Santo, Brazil, using the MICP bacterium Sporosarcina pasteurii contained within a urea-calcium chloride solution inoculum. Investigation, by means of a Rowe cell, of the post-treatment permeability, to untreated control samples, has shown an average decrease in the vertical coefficient of permeability of 83%, from 1.15 × 10-7 m/s for the untreated control samples, to 1.92 × 10-8 m/s in treated samples.

Physical-mechanical properties of microbially induced calcite precipitation-treated loess and treatment mechanism

Loess disintegration can lead to geotechnical engineering problems,e.g.,slope erosion,wetting-induced landslide,and hydroconsolidation.Microbially induced calcite precipitation(MICP)technique is a potential loess reinforcing method.This study investigated the physical-mechanical properties of MICP-treated loess and then explored the mechanism of loess modification by MICP.Here,loess first underwent MICP treatment,i.e.,mixing loess with Sporosarcina pasteurii and cementation solution(CS).Then,the effects of the CS concentration(0.2,0.6,0.8,and 1 M)on the physical and mechanical properties of the MICP-treated loess were tested.Finally,the static contact angle test,scanning electron microscopy(SEM),and X-ray diffractometry(XRD)were conducted to study the mechanism of MICP treatment on loess.Results showed the following property changes of loess after MICP treatment:the liquid limit decreased by 1.7%,the average particle size increased from 6 to 47μm,the specific gravity decreased from 2.65 to 2.43,the unconfined compressive strength increased from 37 to 71 k Pa,and the disintegration time increased from 10 to 25 min.Besides,the shear strength also increased,and the shear strength parameters(cohesion c and internal friction angle?)varied with the CS concentration.The static contact angle tests indicated that the water absorption ability of loess was reduced after MICP treatment.SEM and XRD results verified that the CaCO_(3)from MICP was attributed to the above results.The above findings explained the mechanism of MICP treatment of loess:the CaCO_(3)coats and cements the particles,and fills the pores of loess,improving the strength and water stability of loess.

A comparative study of using two numerical strategies to simulate the biochemical processes in microbially induced calcite precipitation

In this study,we carried out a comparative study of two different numerical strategies for the modeling of the biogeochemical processes in microbially induced calcite precipitation(MICP)process.A simplified MICP model was used,which is based on the mass transport theory.Two numerical strategies,namely the operator splitting(OS)and the global implicit(GI)strategies,were adopted to solve the coupled reactive mass transport problems.These two strategies were compared in the aspects of numerical accuracy,convergence property and computational efficiency by solving the presented MICP model.To look more into the details of the model,sensitivity analysis of some important modeling parameters was also carried out in this paper.

Enzyme-Induced Carbonate Precipitation for the Protection of Earthen Dikes and Embankments Under Surface Runoff: Laboratory Investigations

Earthen structures such as shore protection dikes and river embankments easily suffer from erosion under surface water runoff.This study made experimental efforts to explore the enzyme-induced carbonate precipitation(EICP)method for slope erosion control under surface runoff for earthen structures.The sandy soils were treated by the EICP method for various rounds.Surface characteristics were evaluated by the surface penetration resistance,calcium carbonate content,and surface hard crust thickness of EICP-treated soils.Slope runoff erosion experiments were carried out to evaluate the erosion control performances of the EICP treatment.The surface penetration resistance,calcium carbonate content,and surface hard crust thickness were found to significantly increase with the treatment rounds.In the erosion experiments,it was observed that the level of damages decreased and the water flow volume required to trigger the damage increased with more treatments.The increase in the soil slope angle led to more serious surface damages.The amount and rate that the soil particles were eroded from the slope surfaces declined with more EICP treatments,which was consistent with those of visual observations.The preliminary investigations presented in this study have shown the potential of the EICP method for slope erosion control under surface runoff for earthen structures.

Experimental study on mitigating wind erosion of calcareous desert sand using spray method for microbially induced calcium carbonate precipitation

Wind erosion is one of the significant natural calamities worldwide, which degrades around one-third of global land. The eroded and suspended soil particles in the environment may cause health hazards, i.e.allergies and respiratory diseases, due to the presence of harmful contaminants, bacteria, and pollens.The present study evaluates the feasibility of microbially induced calcium carbonate precipitation(MICP)technique to mitigate wind-induced erosion of calcareous desert sand(Thar desert of Rajasthan province in India). The temperature during biotreatment was kept at 36℃ to stimulate the average temperature of the Thar desert. The spray method was used for bioaugmentation of Sporosarcina(S.) pasteurii and further treatment using chemical solutions. The chemical solution of 0.25 pore volume was sprayed continuously up to 5 d, 10 d, 15 d, and 20 d, using two different concentration ratios of urea and calcium chloride dihydrate viz 2:1 and 1:1. The biotreated samples were subjected to erosion testing(in the wind tunnel) at different wind speeds of 10 m/s, 20 m/s, and 30 m/s. The unconfined compressive strength of the biocemented crust was measured using a pocket penetrometer. The variation in calcite precipitation and microstructure(including the presence of crystalline minerals) of untreated as well as biotreated sand samples were determined through calcimeter, scanning electron microscope(SEM), and energydispersive X-ray spectroscope(EDX). The results demonstrated that the erosion of untreated sand increases with an increase in wind speeds. When compared to untreated sand, a lower erosion was observed in all biocemented sand samples, irrespective of treatment condition and wind speed. It was observed that the sample treated with 1:1 cementation solution for up to 5 d, was found to effectively resist erosion at a wind speed of 10 m/s. Moreover, a significant erosion resistance was ascertained in15 d and 20 d treated samples at higher wind speeds. The calcite content percentage, thickness of crust,bulk density, and surface strength of biocemented sand were enhanced with the increase in treatment duration. The 1:1 concentration ratio of cementation solution was found effective in improving crust thickness and surface strength as compared to 2:1 concentration ratio of cementation solution. The calcite crystals formation was observed in SEM analysis and calcium peaks were observed in EDX analysis for biotreated sand.

Eff ect of Cementation on Calcium Carbonate Precipitation of Loose Sand Resulting from Microbial Treatment

Microbe-induced calcite precipitation is a sustainable improvement technique for sandy soil, which can alter the properties of sand via microbial activity. In this study, we investigated the loose-sand-consolidation effect by controlling the injection velocity, bacterial and cementing-solution concentrations, and hold times. The results demonstrate that, as the cyclic batch increases, the utilization rate of the bacterial fluid increases and both the optical density (OD600) of the bacteria and urease activity decrease. Moreover, it was determined that a 3-h hold time for a 0.5 mol/L cementing solution with a cementing fluid velocity of 2 mL/min has the greatest bonding effect. The final strength of the loose sand with an increase in calcium carbonate content was further discussed. © 2017 Tianjin University and Springer-Verlag GmbH Germany

Biochar-bacteria partnership based on microbially induced calcite precipitation improves Cd immobilization and soil function

Microbially induced calcite precipitation(MICP)technique utilizes ureolytic bacteria to decompose urea and generate carbonate ions for metal combination.MICP can remediate heavy metal(e.g.,Cd)contaminated soils while maintaining or even improving soil functions,but its efficiency in agricultural soil practical application still needs to be enhanced.Here,we constructed a biochar-bacteria(2B)partnership in which biochar provides high nutrition and diverse sorption sites.Using the 2B system,Cd immobilization effectiveness and the underlying mechanism were examined along with the soil properties and soil functions.Results showed that compared to the single biochar and ureolytic bacteria systems,soil Cd mobility was reduced by 23.6%and 45.8%through co-precipitating with CaCO_(3) as otavite(CdCO_(3))in the 2B system,whereas soil fertility,bacterial diversity,and richness increased by 11.7-90.2%,5.4-16.1%,and 6.8-54.7%,respectively.Moreover,the abundances of Proteobacteria and Firmicutes were enhanced in the 2B system.Notably,Sporosarcina and Bacillus(Firmicutes genus)that carry the ureC gene were boosted in the system,further implicating the microbiological mechanism in reducing Cd migration and its bioavailability in soil.Overall,the constructed 2B system was efficient in soil Cd immobilization by strengthening the ureolytic bacteria growth and their nutrient supply in the bacteria-rich soil ecosystem.

低分子量有机酸(苹果酸)对方解石-氟的吸附/沉淀反应影响

低分子量有机酸常对矿物的表面反应(吸附/沉淀)产生影响,从而影响矿物的溶解、矿化等过程,进而影响环境地球化学进程中元素的迁移稳定性。苹果酸作为一种广泛存在于自然界中的有机酸,是植物通过代谢过程分泌的副产品。通过批量平衡法开展了苹果酸对方解石-氟的吸附/沉淀反应的影响研究,旨在深入理解有机酸在地球化学过程中的作用。结果表明:①初始pH值为7.7条件下,对于低浓度氟(≤5 mg·L^(-1)),随着苹果酸浓度的升高,其对氟去除的抑制作用呈增强趋势;对于中、高浓度氟(25或60 mg·L^(-1)),氟去除主导机制为CaF 2沉淀反应,苹果酸的抑制作用对其影响不大,但其表面吸附反应导致pH值升高和钙浓度下降。②初始pH值为8.3条件下,对于低浓度氟(≤20 mg·L^(-1)),苹果酸对氟去除仍有抑制作用;苹果酸与Ca 2+的络合反应促使pH值和钙浓度上升;对于中浓度氟(60 mg·L^(-1)),氟去除主导机制为CaF 2沉淀反应,20 mg·L^(-1)苹果酸已对其产生抑制作用,随着苹果酸浓度继续升高,pH值先降后升,钙浓度持续上升,彰显了苹果酸络合反应的效应;对于高浓度氟(100 mg·L^(-1)),100 mg·L^(-1)苹果酸能极大抑制CaF 2沉淀反应,对应的pH值未超过无苹果酸时,对应的钙浓度仍低于其空白背景值,暗示了CaF 2沉淀反应的主导性。③初始pH值为8.7条件下,对于低浓度氟(≤5 mg·L^(-1)),苹果酸对氟去除的抑制作用有所减弱,但其络合反应产生的效应十分显著,导致pH值和钙浓度上升;对于高浓度氟(240 mg·L^(-1)),氟去除主导机制为CaF 2沉淀反应,该反应随着苹果酸浓度的升高而受到抑制,对应的钙浓度不断上升彰显苹果酸络合反应的效应,而pH值的下降也表明了CaF 2沉淀反应的主导性。本研究深入探讨了氟元素在方解石矿物界面上的吸附、迁移和转化过程,为理解氟的迁移稳定性提供了新的视角和理论基础,同时对富含有机酸环境中方解石矿物的稳定性评估具有重要意义,也为氟在其他矿物上的迁移转化研究提供借鉴。

赤泥对磷石膏生物胶结的充填性能影响研究

为了解决充填骨料磷石膏强酸性劣化生物胶结充填体材料性能的问题,提出引入碱性固废赤泥的方法,探究添加不同质量分数的赤泥对磷石膏生物胶结充填料浆和充填体力学性能的影响。结果显示:在微生物诱导碳酸盐沉淀(Microbially Induced Calcite Precipitation, MICP)作用下,充填骨料中赤泥质量分数从0提高至80%时,充填料浆的泌水率由17%增至44%,表观黏度由585 mPa·s降至121 mPa·s,初、终凝时间分别增加了139%和135%。赤泥质量分数影响磷石膏生物胶结充填体的单轴抗压强度(Uniaxial Compressive Strength, UCS)。当赤泥占骨料总质量的20%时,充填体强度最高,为2 070 kPa,而过高的赤泥添加质量分数会导致UCS降低。强度的变化与赤泥的高碱性和干缩性有关。研究为碱性固废赤泥在磷石膏生物胶结充填中的应用提供理论基础和技术支撑,实现了固废资源化利用。

Modelling of the elastoplastic behaviour of the bio-cemented soils using an extended Modified Cam Clay model

An elastoplastic constitutive model based on the Modified Cam Clay(MCC)model is developed to describe the mechanical behaviour of soils cemented via microbially induced calcite precipitation(MICP).It considers the increase of the elastic stiffness,the change of the yield surface due to MICP cementation and the degradation of calcium carbonate bonds during shearing.Specifically,to capture the typical contraction-dilation transition in MICP soils,the original volumetric hardening rule in the MCC model is modified to a combined deviatoric and volumetric hardening rule.The model could reproduce a series of drained triaxial tests on MICP-treated soils with different calcium carbonate contents.Further,we carry out a parametric study and observe numerical instability in some cases.In combination with an analytical analysis,our numerical modelling has identified the benefits and limitations of using MCCbased models in the simulation of MICP-cemented soils,leading to suggestions for further model development.

沸石增强砂土微生物固化效果研究

为提高砂土的微生物固化效果,考虑沸石作为吸附材料具有多孔的特性,通过宏观物理力学试验和微细观检测,系统分析了沸石对微生物固化砂土的增强效果。研究结果表明:沸石能够显著提高砂土微生物加固过程中的固菌率。与常规微生物固化相比,掺入沸石后,固菌率提升约5.5倍,抗压强度提升39.35%,渗透系数减小71.94%。掺入沸石,一方面能够增加碳酸钙沉淀生成量,并改善其分布均匀性;另一方面,沸石周围的碳酸钙沉淀对两侧砂颗粒起到良好的桥接作用,能够增强砂颗粒之间的结构性及试样的整体性。研究成果为进一步优化微生物诱导碳酸钙沉积技术提供参考。

冻融循环作用下MICP固化铅污染土的强度与浸出特性研究

微生物诱导碳酸钙沉淀(MICP)技术可用于重金属污染土固化稳定修复。本文通过开展无侧限抗压强度、离子浸出及微观试验,主要研究MICP固化铅污染土在冻融循环作用下的强度与化学稳定性,并揭示其微观作用机理。结果表明:随着铅离子浓度的增加,土体的无侧限抗压强度先增大后减小,铅离子浸出浓度增大;随冻融循环次数的增加,土体的强度逐渐降低并趋于稳定,铅离子浸出浓度增大。冻融循环作用后,固化土的主要矿物成分未发生变化;土中的小孔隙数量增加,大孔隙数量基本保持不变。冻融循环作用损伤固化土的碳酸钙胶结与铅离子沉淀结构,致使土体性能劣化。

微生物加固粉土的强度特性及加固机理研究

针对华北地区广泛分布的黄河冲积粉土级配差、强度低的问题,采用微生物诱导碳酸钙沉淀(MICP)技术对其进行加固。通过三轴试验研究加固粉土的强度特性,通过微观结构测试分析其微观机理;结合宏观现象和微观机理揭示强度加固机理。结果表明:MICP加固后粉土的强度得到了大幅提升;其黏聚力和内摩擦角均随加固轮数、胶结液浓度的增加而增大,且增长速率呈现出先快后慢的趋势;在胶结液浓度为0.5 mol/L、加固两轮时加固效率更高。就微观结构而言,土样中的孔隙随胶结液浓度和加固轮数的增大而逐渐减少;土样截面的平均非孔隙面积比随加固轮数、胶结液浓度的增加而增大;黏聚力、内摩擦角与平均非孔隙面积比之间均符合先快后慢的双线性增加关系。黏聚力与内摩擦角提升原因在于MICP加固生成的碳酸钙通过粘结粉土颗粒,填充堵塞颗粒间孔隙,使平均非孔隙面积比增大,进而提升土体强度。

微生物诱导碳酸钙沉淀技术对花岗岩残积土渗透性的影响规律研究

用花岗岩残积土填筑的路基具有水稳性差、渗透系数大、易受降雨冲刷等特点。为探讨微生物诱导碳酸钙沉淀(microbial induced calcite precipitation,MICP)技术对花岗岩残积土渗透系数的影响规律及作用机理,测定MICP固化前后重塑花岗岩残积土试样的渗透系数,并对固化前后的试样进行碳酸钙质量分数测定、核磁共振扫描、电镜扫描以及X射线衍射分析。结果表明:1) MICP技术能使花岗岩残积土试样的渗透系数降低两个数量级,且在试验范围内,将各因素按照对渗透系数的影响程度从大到小排列,依次为:胶结液浓度、固化次数、灌注液量。同时,最佳固化条件为灌注液量40 mL、胶结液浓度1.0 mol/L、固化16次。2)固化产生的沉淀填充在花岗岩残积土孔隙中,致使孔隙间的连通性变差,孔隙率下降。总体上,越靠近注入端碳酸钙的质量分数越大,固化效果越好。3)簇状的方解石碳酸钙有效胶结了原本松散的土颗粒,堵塞了土颗粒孔隙间的渗流通道,降低了试样的渗透系数。

开放系统下方解石除氟机制的主导性界定研究

方解石除氟机制主要涉及表面吸附和沉淀2个方面,宏观界定以上2种机制在除氟过程中的主导性,对氟去除后的稳定性评估有重要意义。文章采用批量平衡法,在不同pH、时间、氟浓度等条件下,对开放体系中方解石除氟机制的主导性进行界定研究。结果表明:(1)在pH8.3条件下,初始氟浓度≤40 mg/L,表面吸附为氟去除的主导机制,该反应3 h内便基本完成;初始氟浓度≥60 mg/L,CaF_(2)沉淀反应作为除氟的主导机制,该主导性在3 h后已体现出来,24 h后反应仍未达到平衡;Langmuir和Freundlich模型拟合结果与上述结果一致。(2)在pH7.7条件下,初始氟浓度≤10 mg/L,表面吸附作为除氟的主导机制,反应在3 h内也基本完成;当初始氟浓度≥25mg/L时,氟去除的主导机制为CaF_(2)沉淀反应,对应Ca浓度和pH值的变化趋势印证了该沉淀反应的主导性,3 h后反应基本完成。(3)在pH7.3条件下,初始氟浓度≤5 mg/L时,氟去除的主导机制为表面吸附,该反应在3 h内也基本完成;当初始氟浓度≥10 mg/L,氟去除的主导机制已转变为沉淀反应,反应在3 h内也基本完成,与pH7.7条件时类似。对应的Ca浓度和pH值并未产生重大变化,与pH7.7时情况不同。(4)氟的去除率结果指出,不管反应3 h还是24 h后,氟的去除率曲线总出现拐点,暗示了氟去除的主导机制由表面吸附向沉淀转变,与上述氟去除动力学结果一致。通过对2种除氟机制主导性的宏观界定,为今后氟的迁移稳定性研究提供借鉴。

微生物改良膨胀土的胀缩性及耐水性试验研究

为了探索微生物诱导碳酸钙沉淀技术对膨胀土的改良效果,开展了微生物改良膨胀土的胀缩试验、崩解试验和冲刷试验,分析了微生物固化对膨胀土的自由膨胀率、无荷载膨胀率、有荷载膨胀率、收缩率、收缩系数、缩限和耐水性的影响。研究结果表明,随着微生物诱导生成的碳酸钙含量的增加,膨胀土的膨胀率、收缩率、崩解量、冲刷量均有明显降低;总体上,养护前7 d各项指标降低迅速,养护15 d之后变化较小。