Suffusion refers to the loss of fineparticles within the soil matrix without any associated volume change,induced by hydrodynamic forces.This study investigated the suffusion of sand-clay mixtures through one-dimensio...Suffusion refers to the loss of fineparticles within the soil matrix without any associated volume change,induced by hydrodynamic forces.This study investigated the suffusion of sand-clay mixtures through one-dimensional soil column experiments under a stepwise increase in hydraulic gradient(i),aiming to evaluate the critical hydraulic gradient(icrit)as a function of the size ratio between sand and clay,clay type,and ionic concentration.It was found that icrit was less than 0.1 for all sand-clay mixtures examined in this study.In addition,the lower peak concentrations of filtrated clay observed in sand-illite mixtures,compared to those of sand-kaolinite mixtures at the same level of i,suggest that illite particles are more susceptible to suffusion.Overall,the observed breakthrough curves,mass fraction of filtrated clay,volume of outflow,and total injection time presented in this study highlight the importance of considering clay type,sand-to-clay size ratio,and ionic concentration when assessing the suffusion behavior of clay-containing soils under a stepwise increase in hydraulic gradient.展开更多
In this study,the dynamic characteristics and microstructures of lacustrine soft clays were studied.Dynamic character tests were conducted on undisturbed,remolded,and saturated lacustrine soft clays,using a dynamic tr...In this study,the dynamic characteristics and microstructures of lacustrine soft clays were studied.Dynamic character tests were conducted on undisturbed,remolded,and saturated lacustrine soft clays,using a dynamic triaxial tester.A scanning electron microscope(SEM)was employed to assess the soil samples after dynamic testing.The results indicate that the dynamic characteristics of lacustrine soft clay were significantly affected by confining pressure and water content.A quantitative relationship was established among confining pressures,water content,and the dynamic shear modulus ratio.The dynamic characteristic parameters of undisturbed,remolded and saturated soil are obviously different,and the original structure can enhance the shear strength of soil.By comparing the results with those from other studies,we found that the dynamic characters of soft clays were considerably varied in different regions,and lacustrine soft clays had a larger dynamic shear modulus ratio and a smaller damping ratio when the dynamic shear strain was large.Using IPP software to process the microstructural images,we found that the soil was dominated by small pores and medium particles,and the roundness of pores and particles had an apparently positive correlation with the maximum diameter.Moreover,the pores and particles of the soil showed fractal characteristics and directionality,and the fractal dimensions and probability entropy were strongly correlated with the macrostructural parameters.Finally,we developed a prediction model for macrostructural and microstructural parameters.展开更多
Estimating the properties of foam-conditioned clay soils is important for both conditioning and recycling goals in earth pressure balance(EPB)shield tunneling.In this study,the vacuum dewatering behaviors of foam-cond...Estimating the properties of foam-conditioned clay soils is important for both conditioning and recycling goals in earth pressure balance(EPB)shield tunneling.In this study,the vacuum dewatering behaviors of foam-conditioned clay soils were investigated,with their potential use as an alternative means to assess foam optimization being examined.A series of laboratory and fieldtests was conducted,including vacuum dewatering tests that considered the effects of filtrationtime and pressure,vane shear tests,and improved cone pullout tests under different gravimetric water content(w)and foam injection ratio(FIR)conditions.It was found that the filtrate loss(FL),which characterizes dewaterability,was increased by extended vacuum filtrationtime and elevated pressure.While increases in w and FIR enhanced FL,reductions were observed in the undrained shear strength(cu),tangential adhesion stress(Fs),and normal adhesion stress(Fn).Furthermore,a linear decrease in FL with increasing mechanical indices(cu,Fs,and Fn)was demonstrated by both laboratory and fielddata fittingresults,regardless of w,FIR,and dewatering conditions.This study provides novel insights into the understanding of vacuum dewatering mechanisms in foam-conditioned clay soils,while a simple approach is proposed for evaluating foam conditioning effectiveness in EPB shield tunneling applications.展开更多
Soft clay treatment with all industrial by-product(IBP)binder has great economic and environmental benefits,yet its geomechanics and mechanisms still need to be well probed.With the activation by calcium carbide resid...Soft clay treatment with all industrial by-product(IBP)binder has great economic and environmental benefits,yet its geomechanics and mechanisms still need to be well probed.With the activation by calcium carbide residue(CCR)and phosphogypsum(PG),the strength,structure,and mechanisms of soft clay treated by aluminosilicate-rich IBP(AS-IBP,such as ground granulated blast furnace slag(GGBS),fly ash(FA),coal gangue(CG),Bayer red mud(BR),and sintered red mud(SR))are comparatively investigated.The strength characteristics of solidified clay exhibit significant differences as AS-IBP changes.When GGBS is adopted,the strength is sensitive to the change in PG content,while the impact of CCR is insignificant.After 90 d,the strength of the optimal sample(G23)reaches 1.40 MPa,35.9%higher than cement solidified clay(CSC),while that achieved by other AS-IBPs is less than 0.3 MPa.In the compression test,the structure's evolutionary trend of G23 has a sudden change as the strength increases from 1.81 MPa to 2.29 MPa,suggesting the transformation in material properties.Besides,the structure of G23 is stronger than CSC,which contributes more to the compressive performance.The total amount of main products(C-S-H and ettringite)of all-IBP solidified clay determines the strength,and ettringite is only significant when calcium-rich AS-IBP is adopted.The total amount of minor products(C-A-H and C-A-S-H)is similar for different samples,equivalent to 28.9%-46.3%of the main products.The relationship between the strength and the product amount can be presented using an exponential function.展开更多
The utilization of solid wastes to prepare Li_(4)SiO_(4) based CO_(2) adsorbents and thermochemical energy storage(TES)materials has recently garnered significant interest.Considering practical application conditions,...The utilization of solid wastes to prepare Li_(4)SiO_(4) based CO_(2) adsorbents and thermochemical energy storage(TES)materials has recently garnered significant interest.Considering practical application conditions,the influence of CO_(2) concentration and temperature fluctuations on adsorbent performance remains a key research focus.Among various waste materials,waste clay bricks are particularly suitable for Li_(4)SiO_(4) synthesis due to their high SiO_(2) content(60% to 70%),while enabling waste valorization.Furthermore,it has been demonstrated that heteroatoms present in the waste materials positively in-fluence the CO_(2) adsorption performance of Li_(4)SiO_(4)-based adsorbents.In this study,Li_(4)SiO_(4) was syn thesized for the first time directly from waste clay bricks without pretreatment.Comprehensive characterization revealed that the resulting Li_(4)SiO_(4)-based adsorbent exhibits outstanding performance:a high CO_(2) capture capacity(27.9%(mass)),excellent cycling stability,and remarkable thermal energy storage capability(876.4 kJ·kg^(-1)).These superior properties position it as one of the most promising high-temperature adsorbents for simultaneous CO_(2) capture and thermal energy storage(TES)from fossil fuel flue gase.Moreover,the adsorbent maintained excellent stability under fluctuating temper-ature and CO_(2) concentration.Even at 20%(vol)CO_(2) and 500℃,it achieved a high capacity of 25.7%(mass),reaching equilibrium within 15 min.This CO_(2) capture performance is truly impressive.展开更多
It has been well recognized that sand particles significantly affect the mechanical properties of reconstituted sandy clays,including the hosted clay and sand particles.However,interrelation between the permeability a...It has been well recognized that sand particles significantly affect the mechanical properties of reconstituted sandy clays,including the hosted clay and sand particles.However,interrelation between the permeability and compressibility of reconstituted sandy clays by considering the structural effects of sand particles is still rarely reported.For this,a series of consolidation-permeability coefficient tests were conducted on reconstituted sandy clays with different sand fractions(ψ_(ss)),initial void ratio of hosted clays(e_(c0))and void ratio at liquid limit of hosted clays(e_(cL)).The roles of ψ_(ss) in both the relationships of permeability coefficient of hosted clay(k_(v-hosted clay))versus effective vertical stress(σ'_(v))and void ratio of hosted clay(e_(c-hosted clay))versus σ'_(v) were analyzed.The results show that the permeability coefficient of reconstituted sandy clays(k_(v))is dominated by hosted clay(k_(v)=k_(v-hosted clay)).Both ψ_(ss) and σ'_(v) affect the k_(v) of sandy clays by changing the e_(c-hosted clay) at any given σ'_(v).Due to the partial contacts and densified clay bridges between the sand particles(i.e.structure effects),the e_(c-hosted clay) in sandy clays is higher than that in clays at the same σ'_(v)v.The k_(v)-e_(c-hosted clay) relationship of sandy clays is independent of σ'_(v) and ψ_(ss)but is a function of e_(cL).The types of hosted clays affect the k_(v) of sandy clays by changing the e_(cL).Based on the relationship between permeability coefficient and void ratio for the reconstituted clays,an empirical method for determining the k_(v) is proposed and validated for sandy clays.The predicted values are almost consistent with the measured values with k_(v-predicted)=k_(v-measured)=0.6-2.5.展开更多
Interactions between cement clinkers and clay minerals are crucial to the much lower strength of cement-based stabilized clays than concrete or mortar.In this paper,the kaolinite-based and montmorillonite-based clays ...Interactions between cement clinkers and clay minerals are crucial to the much lower strength of cement-based stabilized clays than concrete or mortar.In this paper,the kaolinite-based and montmorillonite-based clays were respectively stabilized by tricalcium silicate(C3S)and tricalcium aluminate(C3A),and measured by the unconfined compressive strength(UCS),29Si/27Al solid state nuclear magnetic resonance(SS-NMR),Fourier transform infrared spectroscopy(FTIR),and transmission electron microscope(TEM)to probe the clinker-clay mineral interaction from macro-mechanical,mineralogical,and microstructural perspectives.The results show that C3A-stabilized samples gain strength rapidly in the first 3 d but are only 20%e60%of the strength of C3S-stabilized ones after 60 d.Microstructures reveal that montmorillonite shows better pozzolanic reactivity due to its superior Sichain and lattice substitution compared to kaolinite.This interaction domains the engineering performance of stabilized clays,benefiting the design of stabilizer referring to as the industrial by-products and clay minerals.展开更多
Suffusion is the process defined as the migration of relatively small soil particles through the pores of a soil matrix composed of relatively large particles,driven by substantial hydrodynamic forces and weak attract...Suffusion is the process defined as the migration of relatively small soil particles through the pores of a soil matrix composed of relatively large particles,driven by substantial hydrodynamic forces and weak attraction energies.This study investigates the influence of flow direction(upward and downward)on suffusion induced by interaction energies in sand-clay mixtures under both saturated and unsaturated conditions.The impact of clay mineralogy(kaolinite,illite,and montmorillonite),sand-grain size,and ionic concentration(IC)gradient were discussed based on the observed breakthrough curves(BTCs)and relative saturation rate(Sr)during injection(particularly for unsaturated conditions).Under saturated conditions,higher susceptibility to suffusion was observed in sand-kaolinite and sand-illite mixtures under downward flow compared to upward flow,whereas the suffusion of montmorillonite was more significant under upward flow than under downward flow.In contrast,for unsaturated conditions,more substantial suffusion of kaolinite and illite particles occurred under upward flow compared to downward flow,whereas the opposite trend was observed in sand-montmorillonite mixtures.In addition,the impact of sand-grain size(or the size ratio between sand and clay)on the suffusion of kaolinite and illite under unsaturated conditions suggests a reduced size ratio that leads to relatively significant suffusion under downward flow compared to upward flow.The findings presented in this study contribute to a comprehensive understanding of the influence of flow direction on suffusion in sand-clay mixtures under both saturated and unsaturated conditions.展开更多
Open caissons are widely used in foundation engineering because of their load-bearing efficiency and adaptability in diverse soil conditions.However,accurately predicting their undrained bearing capacity in layered so...Open caissons are widely used in foundation engineering because of their load-bearing efficiency and adaptability in diverse soil conditions.However,accurately predicting their undrained bearing capacity in layered soils remains a complex challenge.This study presents a novel application of five ensemble machine(ML)algorithms-random forest(RF),gradient boosting machine(GBM),extreme gradient boosting(XGBoost),adaptive boosting(AdaBoost),and categorical boosting(CatBoost)-to predict the undrained bearing capacity factor(Nc)of circular open caissons embedded in two-layered clay on the basis of results from finite element limit analysis(FELA).The input dataset consists of 1188 numerical simulations using the Tresca failure criterion,varying in geometrical and soil parameters.The FELA was performed via OptumG2 software with adaptive meshing techniques and verified against existing benchmark studies.The ML models were trained on 70% of the dataset and tested on the remaining 30%.Their performance was evaluated using six statistical metrics:coefficient of determination(R²),mean absolute error(MAE),root mean squared error(RMSE),index of scatter(IOS),RMSE-to-standard deviation ratio(RSR),and variance explained factor(VAF).The results indicate that all the models achieved high accuracy,with R²values exceeding 97.6%and RMSE values below 0.02.Among them,AdaBoost and CatBoost consistently outperformed the other methods across both the training and testing datasets,demonstrating superior generalizability and robustness.The proposed ML framework offers an efficient,accurate,and data-driven alternative to traditional methods for estimating caisson capacity in stratified soils.This approach can aid in reducing computational costs while improving reliability in the early stages of foundation design.展开更多
Natural gas hydrates widely accumulate in submarine sediments composed of clay minerals.However,due to the complex physiochemistry and micron-sized particles of clay minerals,their effects on methane hydrate(MH)format...Natural gas hydrates widely accumulate in submarine sediments composed of clay minerals.However,due to the complex physiochemistry and micron-sized particles of clay minerals,their effects on methane hydrate(MH)formation and dissociation are still in controversy.In this study,montmorillonite and illite were separately mixed with quartz sand to investigate their effects on MH formation and dissociation.The microstructure of synthesized samples was observed by cryo-SEM innovatively to understand the effects of montmorillonite and illite on MH phase transition in micron scale.Results show that montmorillonite and illite both show the inhibition on MH formation kinetics and water-to-hydrate conversion,and illite shows a stronger inhibition.The 10 wt%montmorillonite addition significantly retards MH formation rate,and the 20 wt%montmorillonite has a less inhibition on the rate.The increase of illite mass ratio(0-20 wt%)retards the rate of MH formation.As the content of clay minerals increase,the water-to-hydrate conversion decreases.Cryo-SEM images presented that montmorillonite aggregates separate as individual clusters while illite particles pack as face-to-face configuration under the interaction with water.The surface-overlapped illite aggregates would make sediments pack tightly,hinder the contact between gas and water,and result in the more significant inhibition on MH formation kinetics.Under the depressurization method,the addition of clay minerals facilitates MH dissociation rate.Physicochemical properties of clay minerals and MH distribution in the pore space lead to the faster dissociation rate in clay-containing sediments.The results of this study would provide beneficial guides on geological investigations and optimizing strategies of natural gas production in marine hydrate-bearing sediments.展开更多
As a widely used fertilizer,urea significantly promotes the leaching of dissolved organic nitrogen(DON)in soils and aggravates nitrogen contamination in groundwater.Clayminerals are considered the most important facto...As a widely used fertilizer,urea significantly promotes the leaching of dissolved organic nitrogen(DON)in soils and aggravates nitrogen contamination in groundwater.Clayminerals are considered the most important factor in retaining DON.However,the effect of urea on the retention of DON with different molecular weights by clay minerals is unknown.In this study,the retention of both low-molecular weight DON(LMWD)and high-molecular weight DON(HMWD)by clay minerals in the presence of urea was investigated.For this purpose,batch adsorption and soil column leaching experiments,characterization analysis(Fourier transform infrared spectroscopy X-ray diffraction,and X-ray photoelectron spectroscopy),and molecular dynamics simulations were carried out.Urea had a positive effect on the adsorption of LMWD,whereas a competitive effect existed for the adsorption of HMWD.The dominant interactions among DON,urea,and clay minerals included H-bonding,ligand exchange,and cation exchange.The urea was preferentially adsorbed on clay minerals and formed a complex,which provided more adsorption sites to LMWD and only a few to HMWD.The presence of urea increased the retention of LMWD and decreased the retention of HMWD in clay minerals.The retention capacity of LMWD increased by 6.9%–12.8%,while that of HMWD decreased by 6.7%–53.1%.These findings suggest that LMWD tended to be trapped in soils,while HMWD was prone to be leached into groundwater,which can be used to evaluate the leaching of DON from soil to groundwater.展开更多
The presence of heavy metals in soil negatively impacts its mechanical properties.Reactive MgO carbonation presents a promising approach to enhance the solidification of Pb-contaminated sandy soils.However,the mechani...The presence of heavy metals in soil negatively impacts its mechanical properties.Reactive MgO carbonation presents a promising approach to enhance the solidification of Pb-contaminated sandy soils.However,the mechanical properties and structural behavior of contaminated soils during carbonation can vary significantly due to differences in soil composition.This study examines the potential application and underlying mechanisms of reactive MgO carbonation in improving the mechanical properties of Pb-contaminated red clay.The findings demonstrate that Pb-contaminated red clay transitions from a plastic to a brittle state following reactive MgO carbonation.After 1 h of treatment,the strength of the red clay exceeded 3 MPa,even at high Pb^(2+)concentrations.The deformation modulus to unconfined compressive strength(UCS)ratio was calculated to be 37.761,with the failure strain primarily ranging from 1.5%to 4.0%.A strength prediction model for the reactive MgO-stabilized Pb-contaminated red clay was proposed,which showed good predictive accuracy.Furthermore,reactive MgO carbonation significantly reduced the Pb leaching concentration in the high-level Pb-contaminated soil to below 0.1 mg/L.Microscopic analysis revealed that an optimal amount of hydrated magnesium carbonates(HMCs)formed a stable and compact structure with the soil particles.However,long-term carbonation causes red clay particles to become sandy,and excessive HMCs can harm the soil structure.Therefore,to maximize the strength improvement while avoiding structural damage,the carbonation time should be controlled to 1 h.展开更多
Numerous former military sites worldwide require environmental cleanup from buried unexploded ordnance(UxO)that pose hazards such as leaching toxic chemicals and explosion risks.However,selecting the appropriate mitig...Numerous former military sites worldwide require environmental cleanup from buried unexploded ordnance(UxO)that pose hazards such as leaching toxic chemicals and explosion risks.However,selecting the appropriate mitigation technology relies on prior knowledge of UxO depth of burial(DoB)at specific sites.This study utilizes numerical simulations,employing large deformation explicit finite element(LDEFE)analysis and the Coupled Eulerian-Lagrangian(CEL)approach,to model the penetration of ordnances into clay targets.A modified Tresca constitutive model is implemented in ABAQUS software to capture key features of clay behavior under high strain rate(HSR)loading.The role of various parameters on DoB is investigated,including undrained shear strength,stiffness,and density of the soil.The findings highlight the paramount importance of undrained shear strength in clayey soil penetrability,in addition to the role of soil stiffness,and density.The simulations were employed to calibrate model parameters for Young's empirical penetration model,as well as the Poncelet phenomenological penetration model,demonstrating the efficacy of the numerical simulations in extrapolating its findings within the relevant parameter space.In particular,the calibrated parameters of Young's and Poncelet's models can be identified as a direct function of the various discussed soil properties,which was previously unavailable.展开更多
This study aims to perform thermophysical characterization,thermogravimetric analysis,and specific surface area determination of a lime-stabilized mixture composed of previously studied Gaoui clay and Michemirédi...This study aims to perform thermophysical characterization,thermogravimetric analysis,and specific surface area determination of a lime-stabilized mixture composed of previously studied Gaoui clay and Michemirédiatomite.Lime stabilization of clay is a widespread technique;the addition of diatomite significantly reduced the mixture’s thermophysical properties due to its porous structure.The absolute density was determined using a helium pycnometer,and the specific surface area,air permeability test,was also determined using a Blaine permeabilimeter.Experimental results showed that the thermal conductivity and thermal effusivity of the clay decreased significantly with the addition of the other two materials.They decreased from 0.74 W/m·K to 0.338 W/m·K and from 985.5 W/s^(1/2)/m^(2)/K to 519.6 W/s^(1/2)/m^(2)/K respectively,for the 100%clay and 50%clay+35%diatomite+15%lime formulations,at a compaction pressure of 3 MPa.Thermogravimetric analysis showed that at low temperatures(0 to 150℃),free water from the materials began to evaporate.From medium temperatures(400 to 600℃)to high temperatures(1,000℃),the results showed a mass loss of 6%for Gaoui clay,2%for Michemirédiatomite,and 1.5%for lime.The results of the Blaine test and air permeability tests demonstrated that the specific surface area of 100%clay is high at 0.355 m^(2)/kg,followed by that of 100%diatomite at 0.305 m^(2)/kg and that of 100%lime at 0.273 m^(2)/kg.展开更多
Clays are a constituent of the earth. As a result, the discovery and traditional use of clays in construction and pottery worldwide dates back to antiquity. Guinea has several deposits of clay minerals whose chemical ...Clays are a constituent of the earth. As a result, the discovery and traditional use of clays in construction and pottery worldwide dates back to antiquity. Guinea has several deposits of clay minerals whose chemical and mineralogical compositions have been little studied. Despite lacking of scientific data on these clay minerals, they are used today in pottery and habitat construction. As a step towards promoting the use of clay materials in Guinea, we conducted a study of the physicochemical and mineralogical properties of three natural clays from Kakan in the Republic of Guinea (AKKB, AKKE, AKKO) used in habitat construction. The aims of this work were to better understand their properties, but above all to be able to act on them to improve and broaden their applications, which until now have been limited to construction. These clays were studied by X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF), moisture content (%W), laser granulometry, Atterberg limits, specific surface area, infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermogravimetric analysis and differential thermal analysis (TGA/DTA). These analyses revealed that the main clay minerals present in our samples are kaolinite, illite and, montmorillonite, with the addition of impurities, the most abundant of which is quartz.展开更多
Clay swelling and fines migration pose significant challenges to thermally enhanced oil recovery(EOR)operations,particularly in clay-rich formations.This study systematically investigates clay swelling behavior and pe...Clay swelling and fines migration pose significant challenges to thermally enhanced oil recovery(EOR)operations,particularly in clay-rich formations.This study systematically investigates clay swelling behavior and permeability impairment under high-temperature,low-salinity(HTLS) conditions and evaluates various inhibition methods to mitigate formation damage.To ensure realistic analysis,data and materials from a field with similar issues in Kazakhstan were used.Static/dynamic swelling tests demonstrated that a quaternary ammonium-based inhibitor consistently provided superior clay stabilization through effective ion exchange and surface charge modification mechanisms.In distilled water at 100℃,inhibitor-treated samples maintained 48.89 % of their original permeability,while untreated samples exhibited severe damage,retaining only 17.05 %.Additionally,this chemical inhibitor significantly lowered the critical salt concentration(CSC),effectively stabilizing clay at 4920 ppm salinity compared to 7380 ppm required without treatment.Scanning electron microscopy(SEM) imaging corroborated these results,revealing that inhibitor-treated clay maintains a compact and coherent structure,in stark contrast to the pronounced swelling,delamination,and structural deterioration observed in untreated clay samples.Nevertheless,this quaternary ammonium-based clay stabilizer presents a robust and promising solution for reducing clay swelling-induced damage,sustaining reservoir permeability,and improving thermal EOR performance in swelling-prone formations.展开更多
In Switzerland,the Opalinus Clay has been selected as a potential host rock for the deep geological disposal of radioactive waste due to its low hydraulic conductivity and favorable swelling properties.During the oper...In Switzerland,the Opalinus Clay has been selected as a potential host rock for the deep geological disposal of radioactive waste due to its low hydraulic conductivity and favorable swelling properties.During the operational phase of the repository,the host rock will be exposed to pH values as high as 13.5 due to concrete degradation,which will certainly affect its hydraulic properties.This study investigates the effect of pH increase on the water retention properties of Opalinus Clay.A series of samples from the lower sandy facies of the Mont Terri site in Switzerland,at initial dry state,were exposed to a hyperalkaline solution of pH=13.5 and to the synthetic water of pH=7.5 at different water contents.After equilibrium,the total suction was measured with a dew point potentiometer and microstructural analyses were conducted via mercury intrusion porosimetry(MIP)and nitrogen adsorption-desorption technique.It was found that the total suction decreased with hydration and pH increase.Since the two investigated solutions have the same osmotic suction,the decrease in total suction was attributed to the decrease in matric suction.Indeed,the total porosity increased with saturation and pH increase.This was confirmed by MIP data that evidenced an increase in the proportion of macropores,and by Barret eJoynereHalenda(BJH)data that showed mesopore generation.The specific surface area(SSA)also increased.The previous results were due to mineral hydration and,exclusively in the case of alkaline solution,to(1)the dissolution of quartz and calcite and(2)the acid-base reactions,which were concentrated at the edges of the clay particles,leading to an increase in negatively charged groups and thus to a face-to-face association of the clay particles(dispersion),causing an increase in the repulsive forces between the clay particles.In addition,the weakening of covalent bonds led to the primary dissolution of clay minerals,i.e.silicon and aluminum detachment.展开更多
This study evaluates the influence of sand content on the mechanical behavior and water resistance of compressed earth bricks(CEBs)manufactured from Lendi clay(Douala,Cameroon).Twenty-seven specimens(prismatic and cub...This study evaluates the influence of sand content on the mechanical behavior and water resistance of compressed earth bricks(CEBs)manufactured from Lendi clay(Douala,Cameroon).Twenty-seven specimens(prismatic and cubic)were produced with three formulations:0%,30%and 60%sand substitution by dry mass,compacted at 2.5 MPa and cured for 7,14 and 28 days.Raw material characterization included particle size distribution,sand equivalent,Atterberg limits,bulk density and Proctor compaction.The clay displayed a liquid limit of 44.07%,plastic limit of 35.23%and plasticity index of 8.84%;optimum moisture content was 15.9%and maximum dry density 1.24 g·cm^(-3).Mechanical testing showed that pure-clay bricks achieved the highest compressive and flexural strengths at all ages(up to≈1.98 MPa and 0.56 MPa respectively).Although the 30%sand mix exhibited marginally higher early compressive strength(7 days),strength decreased substantially by 28 days.Capillary absorption tests revealed an important distinction:while 0%sand bricks exhibited continuous water uptake,they retained cohesion during immersion;conversely,30%and 60%sand bricks disintegrated into a slurry within seconds of immersion,evidencing severe loss of internal bonding.These findings indicate that,for this highly plastic tropical clay,sand acts primarily as a microstructural diluent that undermines long-term cohesion and durability despite short-term packing benefits.The study underscores the need for locally tailored formulations or stabilizers when designing durable CEBs for humid tropical climates.展开更多
This work aims to investigate the thermo-poromechanical behavior of saturated silt clay(SC)under varying temperatures through experiments and constitutive modeling.A series of undrained triaxial compression tests was ...This work aims to investigate the thermo-poromechanical behavior of saturated silt clay(SC)under varying temperatures through experiments and constitutive modeling.A series of undrained triaxial compression tests was conducted on saturated SC with temperature ranges from 25℃to 60℃.The effects of temperature on the main poromechanical properties of saturated SC,such as stress-strain relations,pore pressure evolution,and strength parameters,were thoroughly examined.Based on the experimental results,a subtly thermodynamically consistent thermo-poromechanical model was established using the concept of effective plastic stress within the poromechanical framework.Plastic deformation was described with a specific yield criterion and non-associated plastic potential that both depend on the effective plastic stress and a simple hardening variable.Finally,this model was implemented by a semi-implicit return mapping algorithm(SRMA)and validated through the comparison of model predictions and experimental data.The proposed model accurately reproduces the main thermo-poromechanical characteristics observed in saturated SC.展开更多
The presence of clay coatings on the surfaces of quartz grains can play a pivotal role in determining the porosity and permeability of sandstone reservoirs,thus directly impacting their reservoir quality.This study em...The presence of clay coatings on the surfaces of quartz grains can play a pivotal role in determining the porosity and permeability of sandstone reservoirs,thus directly impacting their reservoir quality.This study employs a multiphase-field model of syntaxial quartz cementation to explore the effects of clay coatings on quartz cement volumes,porosity,permeability,and their interrelations in sandstone formations.To generate various patterns of clay coatings on quartz grains within three-dimensional(3D)digital sandstone grain packs,a pre-processing toolchain is developed.Through numerical simulation experiments involving syntaxial overgrowth cementation on both single crystals and multigrain packs,the main coating parameters controlling quartz cement volume are elucidated.Such parameters include the growth of exposed pyramidal faces,lateral encasement,coating coverage,and coating pattern,etc.The coating pattern has a remarkable impact on cementation,with the layered coatings corresponding to fast cement growth rates.The coating coverage is positively correlated with the porosity and permeability of sandstone.The cement growth rate of quartz crystals is the lowest in the vertical orientation,and in the middle to late stages of evolution,it is faster in the diagonal orientation than in the horizontal orientation.Through comparing the simulated results of dynamic evolution process with the actual features,it is found that the simulated coating patterns after 20 d and 40 d show clear similarities with natural samples,proving the validity of the proposed three-dimensional numerical modeling of coatings.The methodology and findings presented contribute to improved reservoir characterization and predictive modeling of sandstone formations.展开更多
基金supported by the National Research Foundation of Korea(NRF)grants(Grant Nos.RS-2020-NR049594 and RS-2022-NR071877)the Korea Agency for Infrastructure Technology Advancement under the Ministry of Land,Infrastructure and Transport(Grant No.RS-2024-00410248).
文摘Suffusion refers to the loss of fineparticles within the soil matrix without any associated volume change,induced by hydrodynamic forces.This study investigated the suffusion of sand-clay mixtures through one-dimensional soil column experiments under a stepwise increase in hydraulic gradient(i),aiming to evaluate the critical hydraulic gradient(icrit)as a function of the size ratio between sand and clay,clay type,and ionic concentration.It was found that icrit was less than 0.1 for all sand-clay mixtures examined in this study.In addition,the lower peak concentrations of filtrated clay observed in sand-illite mixtures,compared to those of sand-kaolinite mixtures at the same level of i,suggest that illite particles are more susceptible to suffusion.Overall,the observed breakthrough curves,mass fraction of filtrated clay,volume of outflow,and total injection time presented in this study highlight the importance of considering clay type,sand-to-clay size ratio,and ionic concentration when assessing the suffusion behavior of clay-containing soils under a stepwise increase in hydraulic gradient.
基金National Natural Science Foundation of China under Grant No.52278340Natural Science Foundation of Hebei Province under Grant No.E2023202028。
文摘In this study,the dynamic characteristics and microstructures of lacustrine soft clays were studied.Dynamic character tests were conducted on undisturbed,remolded,and saturated lacustrine soft clays,using a dynamic triaxial tester.A scanning electron microscope(SEM)was employed to assess the soil samples after dynamic testing.The results indicate that the dynamic characteristics of lacustrine soft clay were significantly affected by confining pressure and water content.A quantitative relationship was established among confining pressures,water content,and the dynamic shear modulus ratio.The dynamic characteristic parameters of undisturbed,remolded and saturated soil are obviously different,and the original structure can enhance the shear strength of soil.By comparing the results with those from other studies,we found that the dynamic characters of soft clays were considerably varied in different regions,and lacustrine soft clays had a larger dynamic shear modulus ratio and a smaller damping ratio when the dynamic shear strain was large.Using IPP software to process the microstructural images,we found that the soil was dominated by small pores and medium particles,and the roundness of pores and particles had an apparently positive correlation with the maximum diameter.Moreover,the pores and particles of the soil showed fractal characteristics and directionality,and the fractal dimensions and probability entropy were strongly correlated with the macrostructural parameters.Finally,we developed a prediction model for macrostructural and microstructural parameters.
基金supported by the National Youth Top-notch Talent Support Program of China(Grant No.00389335)the National Natural Science Foundation of China(Grant No.52378392)the“Foal Eagle Program”Youth Top-notch Talent Project of Fujian Province(Grant No.00387088).
文摘Estimating the properties of foam-conditioned clay soils is important for both conditioning and recycling goals in earth pressure balance(EPB)shield tunneling.In this study,the vacuum dewatering behaviors of foam-conditioned clay soils were investigated,with their potential use as an alternative means to assess foam optimization being examined.A series of laboratory and fieldtests was conducted,including vacuum dewatering tests that considered the effects of filtrationtime and pressure,vane shear tests,and improved cone pullout tests under different gravimetric water content(w)and foam injection ratio(FIR)conditions.It was found that the filtrate loss(FL),which characterizes dewaterability,was increased by extended vacuum filtrationtime and elevated pressure.While increases in w and FIR enhanced FL,reductions were observed in the undrained shear strength(cu),tangential adhesion stress(Fs),and normal adhesion stress(Fn).Furthermore,a linear decrease in FL with increasing mechanical indices(cu,Fs,and Fn)was demonstrated by both laboratory and fielddata fittingresults,regardless of w,FIR,and dewatering conditions.This study provides novel insights into the understanding of vacuum dewatering mechanisms in foam-conditioned clay soils,while a simple approach is proposed for evaluating foam conditioning effectiveness in EPB shield tunneling applications.
基金supported by the National Natural Science Foundation of China(Grant No.U24A20183)Natural Science Fund for Distinguished Young Scholars of Hubei Province,China(Grant No.2024AFA051)Youth Science Fund(A-class)of Hunan Natural Science Foundation of China(Grant No.2025JJ20049).
文摘Soft clay treatment with all industrial by-product(IBP)binder has great economic and environmental benefits,yet its geomechanics and mechanisms still need to be well probed.With the activation by calcium carbide residue(CCR)and phosphogypsum(PG),the strength,structure,and mechanisms of soft clay treated by aluminosilicate-rich IBP(AS-IBP,such as ground granulated blast furnace slag(GGBS),fly ash(FA),coal gangue(CG),Bayer red mud(BR),and sintered red mud(SR))are comparatively investigated.The strength characteristics of solidified clay exhibit significant differences as AS-IBP changes.When GGBS is adopted,the strength is sensitive to the change in PG content,while the impact of CCR is insignificant.After 90 d,the strength of the optimal sample(G23)reaches 1.40 MPa,35.9%higher than cement solidified clay(CSC),while that achieved by other AS-IBPs is less than 0.3 MPa.In the compression test,the structure's evolutionary trend of G23 has a sudden change as the strength increases from 1.81 MPa to 2.29 MPa,suggesting the transformation in material properties.Besides,the structure of G23 is stronger than CSC,which contributes more to the compressive performance.The total amount of main products(C-S-H and ettringite)of all-IBP solidified clay determines the strength,and ettringite is only significant when calcium-rich AS-IBP is adopted.The total amount of minor products(C-A-H and C-A-S-H)is similar for different samples,equivalent to 28.9%-46.3%of the main products.The relationship between the strength and the product amount can be presented using an exponential function.
基金the National Natural Science Foundation of China(5240101142)Yunnan Province basic research project(202401CF070252)+1 种基金the Key R&D plan of Yunnan Province(202303AC100008)the Scientific Researching Fund Projects of Yunnan Provincial Department of Education(2025J0077),which funded this study。
文摘The utilization of solid wastes to prepare Li_(4)SiO_(4) based CO_(2) adsorbents and thermochemical energy storage(TES)materials has recently garnered significant interest.Considering practical application conditions,the influence of CO_(2) concentration and temperature fluctuations on adsorbent performance remains a key research focus.Among various waste materials,waste clay bricks are particularly suitable for Li_(4)SiO_(4) synthesis due to their high SiO_(2) content(60% to 70%),while enabling waste valorization.Furthermore,it has been demonstrated that heteroatoms present in the waste materials positively in-fluence the CO_(2) adsorption performance of Li_(4)SiO_(4)-based adsorbents.In this study,Li_(4)SiO_(4) was syn thesized for the first time directly from waste clay bricks without pretreatment.Comprehensive characterization revealed that the resulting Li_(4)SiO_(4)-based adsorbent exhibits outstanding performance:a high CO_(2) capture capacity(27.9%(mass)),excellent cycling stability,and remarkable thermal energy storage capability(876.4 kJ·kg^(-1)).These superior properties position it as one of the most promising high-temperature adsorbents for simultaneous CO_(2) capture and thermal energy storage(TES)from fossil fuel flue gase.Moreover,the adsorbent maintained excellent stability under fluctuating temper-ature and CO_(2) concentration.Even at 20%(vol)CO_(2) and 500℃,it achieved a high capacity of 25.7%(mass),reaching equilibrium within 15 min.This CO_(2) capture performance is truly impressive.
基金supported by the National Natural Science Foundation of China (Grant Nos.52278334 and 4197724)Fundamental Research Funds for the Central Universities (Grant No.2242024k30066).
文摘It has been well recognized that sand particles significantly affect the mechanical properties of reconstituted sandy clays,including the hosted clay and sand particles.However,interrelation between the permeability and compressibility of reconstituted sandy clays by considering the structural effects of sand particles is still rarely reported.For this,a series of consolidation-permeability coefficient tests were conducted on reconstituted sandy clays with different sand fractions(ψ_(ss)),initial void ratio of hosted clays(e_(c0))and void ratio at liquid limit of hosted clays(e_(cL)).The roles of ψ_(ss) in both the relationships of permeability coefficient of hosted clay(k_(v-hosted clay))versus effective vertical stress(σ'_(v))and void ratio of hosted clay(e_(c-hosted clay))versus σ'_(v) were analyzed.The results show that the permeability coefficient of reconstituted sandy clays(k_(v))is dominated by hosted clay(k_(v)=k_(v-hosted clay)).Both ψ_(ss) and σ'_(v) affect the k_(v) of sandy clays by changing the e_(c-hosted clay) at any given σ'_(v).Due to the partial contacts and densified clay bridges between the sand particles(i.e.structure effects),the e_(c-hosted clay) in sandy clays is higher than that in clays at the same σ'_(v)v.The k_(v)-e_(c-hosted clay) relationship of sandy clays is independent of σ'_(v) and ψ_(ss)but is a function of e_(cL).The types of hosted clays affect the k_(v) of sandy clays by changing the e_(cL).Based on the relationship between permeability coefficient and void ratio for the reconstituted clays,an empirical method for determining the k_(v) is proposed and validated for sandy clays.The predicted values are almost consistent with the measured values with k_(v-predicted)=k_(v-measured)=0.6-2.5.
基金supported by the National Natural Science Foundation of China(Grant Nos.52278334,42272322,and 52209136).
文摘Interactions between cement clinkers and clay minerals are crucial to the much lower strength of cement-based stabilized clays than concrete or mortar.In this paper,the kaolinite-based and montmorillonite-based clays were respectively stabilized by tricalcium silicate(C3S)and tricalcium aluminate(C3A),and measured by the unconfined compressive strength(UCS),29Si/27Al solid state nuclear magnetic resonance(SS-NMR),Fourier transform infrared spectroscopy(FTIR),and transmission electron microscope(TEM)to probe the clinker-clay mineral interaction from macro-mechanical,mineralogical,and microstructural perspectives.The results show that C3A-stabilized samples gain strength rapidly in the first 3 d but are only 20%e60%of the strength of C3S-stabilized ones after 60 d.Microstructures reveal that montmorillonite shows better pozzolanic reactivity due to its superior Sichain and lattice substitution compared to kaolinite.This interaction domains the engineering performance of stabilized clays,benefiting the design of stabilizer referring to as the industrial by-products and clay minerals.
基金supported by the Korea Agency for Infrastructure Technology Advancement under the Ministry of Land,Infrastructure and Transport (Grant No.RS-2024-00410248)by National Research Foundation of Korea (NRF)grants funded by the Korean government (MSIT) (Grant No.RS-2022R1C1C1007296).
文摘Suffusion is the process defined as the migration of relatively small soil particles through the pores of a soil matrix composed of relatively large particles,driven by substantial hydrodynamic forces and weak attraction energies.This study investigates the influence of flow direction(upward and downward)on suffusion induced by interaction energies in sand-clay mixtures under both saturated and unsaturated conditions.The impact of clay mineralogy(kaolinite,illite,and montmorillonite),sand-grain size,and ionic concentration(IC)gradient were discussed based on the observed breakthrough curves(BTCs)and relative saturation rate(Sr)during injection(particularly for unsaturated conditions).Under saturated conditions,higher susceptibility to suffusion was observed in sand-kaolinite and sand-illite mixtures under downward flow compared to upward flow,whereas the suffusion of montmorillonite was more significant under upward flow than under downward flow.In contrast,for unsaturated conditions,more substantial suffusion of kaolinite and illite particles occurred under upward flow compared to downward flow,whereas the opposite trend was observed in sand-montmorillonite mixtures.In addition,the impact of sand-grain size(or the size ratio between sand and clay)on the suffusion of kaolinite and illite under unsaturated conditions suggests a reduced size ratio that leads to relatively significant suffusion under downward flow compared to upward flow.The findings presented in this study contribute to a comprehensive understanding of the influence of flow direction on suffusion in sand-clay mixtures under both saturated and unsaturated conditions.
文摘Open caissons are widely used in foundation engineering because of their load-bearing efficiency and adaptability in diverse soil conditions.However,accurately predicting their undrained bearing capacity in layered soils remains a complex challenge.This study presents a novel application of five ensemble machine(ML)algorithms-random forest(RF),gradient boosting machine(GBM),extreme gradient boosting(XGBoost),adaptive boosting(AdaBoost),and categorical boosting(CatBoost)-to predict the undrained bearing capacity factor(Nc)of circular open caissons embedded in two-layered clay on the basis of results from finite element limit analysis(FELA).The input dataset consists of 1188 numerical simulations using the Tresca failure criterion,varying in geometrical and soil parameters.The FELA was performed via OptumG2 software with adaptive meshing techniques and verified against existing benchmark studies.The ML models were trained on 70% of the dataset and tested on the remaining 30%.Their performance was evaluated using six statistical metrics:coefficient of determination(R²),mean absolute error(MAE),root mean squared error(RMSE),index of scatter(IOS),RMSE-to-standard deviation ratio(RSR),and variance explained factor(VAF).The results indicate that all the models achieved high accuracy,with R²values exceeding 97.6%and RMSE values below 0.02.Among them,AdaBoost and CatBoost consistently outperformed the other methods across both the training and testing datasets,demonstrating superior generalizability and robustness.The proposed ML framework offers an efficient,accurate,and data-driven alternative to traditional methods for estimating caisson capacity in stratified soils.This approach can aid in reducing computational costs while improving reliability in the early stages of foundation design.
基金supported by the Key Research Program of the Institute of Geology&Geophysics,CAS(Grant No.IGGCAS-201903).
文摘Natural gas hydrates widely accumulate in submarine sediments composed of clay minerals.However,due to the complex physiochemistry and micron-sized particles of clay minerals,their effects on methane hydrate(MH)formation and dissociation are still in controversy.In this study,montmorillonite and illite were separately mixed with quartz sand to investigate their effects on MH formation and dissociation.The microstructure of synthesized samples was observed by cryo-SEM innovatively to understand the effects of montmorillonite and illite on MH phase transition in micron scale.Results show that montmorillonite and illite both show the inhibition on MH formation kinetics and water-to-hydrate conversion,and illite shows a stronger inhibition.The 10 wt%montmorillonite addition significantly retards MH formation rate,and the 20 wt%montmorillonite has a less inhibition on the rate.The increase of illite mass ratio(0-20 wt%)retards the rate of MH formation.As the content of clay minerals increase,the water-to-hydrate conversion decreases.Cryo-SEM images presented that montmorillonite aggregates separate as individual clusters while illite particles pack as face-to-face configuration under the interaction with water.The surface-overlapped illite aggregates would make sediments pack tightly,hinder the contact between gas and water,and result in the more significant inhibition on MH formation kinetics.Under the depressurization method,the addition of clay minerals facilitates MH dissociation rate.Physicochemical properties of clay minerals and MH distribution in the pore space lead to the faster dissociation rate in clay-containing sediments.The results of this study would provide beneficial guides on geological investigations and optimizing strategies of natural gas production in marine hydrate-bearing sediments.
基金supported by the National Natural Science Foundation of China(No.42107052)Beijing Natural Science Foundation(No.JQ21031).
文摘As a widely used fertilizer,urea significantly promotes the leaching of dissolved organic nitrogen(DON)in soils and aggravates nitrogen contamination in groundwater.Clayminerals are considered the most important factor in retaining DON.However,the effect of urea on the retention of DON with different molecular weights by clay minerals is unknown.In this study,the retention of both low-molecular weight DON(LMWD)and high-molecular weight DON(HMWD)by clay minerals in the presence of urea was investigated.For this purpose,batch adsorption and soil column leaching experiments,characterization analysis(Fourier transform infrared spectroscopy X-ray diffraction,and X-ray photoelectron spectroscopy),and molecular dynamics simulations were carried out.Urea had a positive effect on the adsorption of LMWD,whereas a competitive effect existed for the adsorption of HMWD.The dominant interactions among DON,urea,and clay minerals included H-bonding,ligand exchange,and cation exchange.The urea was preferentially adsorbed on clay minerals and formed a complex,which provided more adsorption sites to LMWD and only a few to HMWD.The presence of urea increased the retention of LMWD and decreased the retention of HMWD in clay minerals.The retention capacity of LMWD increased by 6.9%–12.8%,while that of HMWD decreased by 6.7%–53.1%.These findings suggest that LMWD tended to be trapped in soils,while HMWD was prone to be leached into groundwater,which can be used to evaluate the leaching of DON from soil to groundwater.
基金supported by the National Key Research and Development Program of China(Grant No.2023YFC3707900)the National Natural Science Foundation of China(Grant Nos.42030710 and 42472337).
文摘The presence of heavy metals in soil negatively impacts its mechanical properties.Reactive MgO carbonation presents a promising approach to enhance the solidification of Pb-contaminated sandy soils.However,the mechanical properties and structural behavior of contaminated soils during carbonation can vary significantly due to differences in soil composition.This study examines the potential application and underlying mechanisms of reactive MgO carbonation in improving the mechanical properties of Pb-contaminated red clay.The findings demonstrate that Pb-contaminated red clay transitions from a plastic to a brittle state following reactive MgO carbonation.After 1 h of treatment,the strength of the red clay exceeded 3 MPa,even at high Pb^(2+)concentrations.The deformation modulus to unconfined compressive strength(UCS)ratio was calculated to be 37.761,with the failure strain primarily ranging from 1.5%to 4.0%.A strength prediction model for the reactive MgO-stabilized Pb-contaminated red clay was proposed,which showed good predictive accuracy.Furthermore,reactive MgO carbonation significantly reduced the Pb leaching concentration in the high-level Pb-contaminated soil to below 0.1 mg/L.Microscopic analysis revealed that an optimal amount of hydrated magnesium carbonates(HMCs)formed a stable and compact structure with the soil particles.However,long-term carbonation causes red clay particles to become sandy,and excessive HMCs can harm the soil structure.Therefore,to maximize the strength improvement while avoiding structural damage,the carbonation time should be controlled to 1 h.
基金the support of the Strategic Environmental Research and Development Program(SERDP)of the United States of America(Grant No.MR23-3855).
文摘Numerous former military sites worldwide require environmental cleanup from buried unexploded ordnance(UxO)that pose hazards such as leaching toxic chemicals and explosion risks.However,selecting the appropriate mitigation technology relies on prior knowledge of UxO depth of burial(DoB)at specific sites.This study utilizes numerical simulations,employing large deformation explicit finite element(LDEFE)analysis and the Coupled Eulerian-Lagrangian(CEL)approach,to model the penetration of ordnances into clay targets.A modified Tresca constitutive model is implemented in ABAQUS software to capture key features of clay behavior under high strain rate(HSR)loading.The role of various parameters on DoB is investigated,including undrained shear strength,stiffness,and density of the soil.The findings highlight the paramount importance of undrained shear strength in clayey soil penetrability,in addition to the role of soil stiffness,and density.The simulations were employed to calibrate model parameters for Young's empirical penetration model,as well as the Poncelet phenomenological penetration model,demonstrating the efficacy of the numerical simulations in extrapolating its findings within the relevant parameter space.In particular,the calibrated parameters of Young's and Poncelet's models can be identified as a direct function of the various discussed soil properties,which was previously unavailable.
文摘This study aims to perform thermophysical characterization,thermogravimetric analysis,and specific surface area determination of a lime-stabilized mixture composed of previously studied Gaoui clay and Michemirédiatomite.Lime stabilization of clay is a widespread technique;the addition of diatomite significantly reduced the mixture’s thermophysical properties due to its porous structure.The absolute density was determined using a helium pycnometer,and the specific surface area,air permeability test,was also determined using a Blaine permeabilimeter.Experimental results showed that the thermal conductivity and thermal effusivity of the clay decreased significantly with the addition of the other two materials.They decreased from 0.74 W/m·K to 0.338 W/m·K and from 985.5 W/s^(1/2)/m^(2)/K to 519.6 W/s^(1/2)/m^(2)/K respectively,for the 100%clay and 50%clay+35%diatomite+15%lime formulations,at a compaction pressure of 3 MPa.Thermogravimetric analysis showed that at low temperatures(0 to 150℃),free water from the materials began to evaporate.From medium temperatures(400 to 600℃)to high temperatures(1,000℃),the results showed a mass loss of 6%for Gaoui clay,2%for Michemirédiatomite,and 1.5%for lime.The results of the Blaine test and air permeability tests demonstrated that the specific surface area of 100%clay is high at 0.355 m^(2)/kg,followed by that of 100%diatomite at 0.305 m^(2)/kg and that of 100%lime at 0.273 m^(2)/kg.
文摘Clays are a constituent of the earth. As a result, the discovery and traditional use of clays in construction and pottery worldwide dates back to antiquity. Guinea has several deposits of clay minerals whose chemical and mineralogical compositions have been little studied. Despite lacking of scientific data on these clay minerals, they are used today in pottery and habitat construction. As a step towards promoting the use of clay materials in Guinea, we conducted a study of the physicochemical and mineralogical properties of three natural clays from Kakan in the Republic of Guinea (AKKB, AKKE, AKKO) used in habitat construction. The aims of this work were to better understand their properties, but above all to be able to act on them to improve and broaden their applications, which until now have been limited to construction. These clays were studied by X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF), moisture content (%W), laser granulometry, Atterberg limits, specific surface area, infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermogravimetric analysis and differential thermal analysis (TGA/DTA). These analyses revealed that the main clay minerals present in our samples are kaolinite, illite and, montmorillonite, with the addition of impurities, the most abundant of which is quartz.
文摘Clay swelling and fines migration pose significant challenges to thermally enhanced oil recovery(EOR)operations,particularly in clay-rich formations.This study systematically investigates clay swelling behavior and permeability impairment under high-temperature,low-salinity(HTLS) conditions and evaluates various inhibition methods to mitigate formation damage.To ensure realistic analysis,data and materials from a field with similar issues in Kazakhstan were used.Static/dynamic swelling tests demonstrated that a quaternary ammonium-based inhibitor consistently provided superior clay stabilization through effective ion exchange and surface charge modification mechanisms.In distilled water at 100℃,inhibitor-treated samples maintained 48.89 % of their original permeability,while untreated samples exhibited severe damage,retaining only 17.05 %.Additionally,this chemical inhibitor significantly lowered the critical salt concentration(CSC),effectively stabilizing clay at 4920 ppm salinity compared to 7380 ppm required without treatment.Scanning electron microscopy(SEM) imaging corroborated these results,revealing that inhibitor-treated clay maintains a compact and coherent structure,in stark contrast to the pronounced swelling,delamination,and structural deterioration observed in untreated clay samples.Nevertheless,this quaternary ammonium-based clay stabilizer presents a robust and promising solution for reducing clay swelling-induced damage,sustaining reservoir permeability,and improving thermal EOR performance in swelling-prone formations.
文摘In Switzerland,the Opalinus Clay has been selected as a potential host rock for the deep geological disposal of radioactive waste due to its low hydraulic conductivity and favorable swelling properties.During the operational phase of the repository,the host rock will be exposed to pH values as high as 13.5 due to concrete degradation,which will certainly affect its hydraulic properties.This study investigates the effect of pH increase on the water retention properties of Opalinus Clay.A series of samples from the lower sandy facies of the Mont Terri site in Switzerland,at initial dry state,were exposed to a hyperalkaline solution of pH=13.5 and to the synthetic water of pH=7.5 at different water contents.After equilibrium,the total suction was measured with a dew point potentiometer and microstructural analyses were conducted via mercury intrusion porosimetry(MIP)and nitrogen adsorption-desorption technique.It was found that the total suction decreased with hydration and pH increase.Since the two investigated solutions have the same osmotic suction,the decrease in total suction was attributed to the decrease in matric suction.Indeed,the total porosity increased with saturation and pH increase.This was confirmed by MIP data that evidenced an increase in the proportion of macropores,and by Barret eJoynereHalenda(BJH)data that showed mesopore generation.The specific surface area(SSA)also increased.The previous results were due to mineral hydration and,exclusively in the case of alkaline solution,to(1)the dissolution of quartz and calcite and(2)the acid-base reactions,which were concentrated at the edges of the clay particles,leading to an increase in negatively charged groups and thus to a face-to-face association of the clay particles(dispersion),causing an increase in the repulsive forces between the clay particles.In addition,the weakening of covalent bonds led to the primary dissolution of clay minerals,i.e.silicon and aluminum detachment.
文摘This study evaluates the influence of sand content on the mechanical behavior and water resistance of compressed earth bricks(CEBs)manufactured from Lendi clay(Douala,Cameroon).Twenty-seven specimens(prismatic and cubic)were produced with three formulations:0%,30%and 60%sand substitution by dry mass,compacted at 2.5 MPa and cured for 7,14 and 28 days.Raw material characterization included particle size distribution,sand equivalent,Atterberg limits,bulk density and Proctor compaction.The clay displayed a liquid limit of 44.07%,plastic limit of 35.23%and plasticity index of 8.84%;optimum moisture content was 15.9%and maximum dry density 1.24 g·cm^(-3).Mechanical testing showed that pure-clay bricks achieved the highest compressive and flexural strengths at all ages(up to≈1.98 MPa and 0.56 MPa respectively).Although the 30%sand mix exhibited marginally higher early compressive strength(7 days),strength decreased substantially by 28 days.Capillary absorption tests revealed an important distinction:while 0%sand bricks exhibited continuous water uptake,they retained cohesion during immersion;conversely,30%and 60%sand bricks disintegrated into a slurry within seconds of immersion,evidencing severe loss of internal bonding.These findings indicate that,for this highly plastic tropical clay,sand acts primarily as a microstructural diluent that undermines long-term cohesion and durability despite short-term packing benefits.The study underscores the need for locally tailored formulations or stabilizers when designing durable CEBs for humid tropical climates.
基金supported by the National Natural Science Foun-dation of China(Grant No.52478335)the 2023 Annual Science and Technology Project of Jiangsu Province Construction System(Grant No.90)the Science and Technology Research and Develop-ment Topic of CSCEC 7th Division(Grant No.CSCEC7b-2024-Z-4).
文摘This work aims to investigate the thermo-poromechanical behavior of saturated silt clay(SC)under varying temperatures through experiments and constitutive modeling.A series of undrained triaxial compression tests was conducted on saturated SC with temperature ranges from 25℃to 60℃.The effects of temperature on the main poromechanical properties of saturated SC,such as stress-strain relations,pore pressure evolution,and strength parameters,were thoroughly examined.Based on the experimental results,a subtly thermodynamically consistent thermo-poromechanical model was established using the concept of effective plastic stress within the poromechanical framework.Plastic deformation was described with a specific yield criterion and non-associated plastic potential that both depend on the effective plastic stress and a simple hardening variable.Finally,this model was implemented by a semi-implicit return mapping algorithm(SRMA)and validated through the comparison of model predictions and experimental data.The proposed model accurately reproduces the main thermo-poromechanical characteristics observed in saturated SC.
基金the Helmholtz association for funding the main parts of the modeling and simulation research work under the program“MTET:38.04.04”。
文摘The presence of clay coatings on the surfaces of quartz grains can play a pivotal role in determining the porosity and permeability of sandstone reservoirs,thus directly impacting their reservoir quality.This study employs a multiphase-field model of syntaxial quartz cementation to explore the effects of clay coatings on quartz cement volumes,porosity,permeability,and their interrelations in sandstone formations.To generate various patterns of clay coatings on quartz grains within three-dimensional(3D)digital sandstone grain packs,a pre-processing toolchain is developed.Through numerical simulation experiments involving syntaxial overgrowth cementation on both single crystals and multigrain packs,the main coating parameters controlling quartz cement volume are elucidated.Such parameters include the growth of exposed pyramidal faces,lateral encasement,coating coverage,and coating pattern,etc.The coating pattern has a remarkable impact on cementation,with the layered coatings corresponding to fast cement growth rates.The coating coverage is positively correlated with the porosity and permeability of sandstone.The cement growth rate of quartz crystals is the lowest in the vertical orientation,and in the middle to late stages of evolution,it is faster in the diagonal orientation than in the horizontal orientation.Through comparing the simulated results of dynamic evolution process with the actual features,it is found that the simulated coating patterns after 20 d and 40 d show clear similarities with natural samples,proving the validity of the proposed three-dimensional numerical modeling of coatings.The methodology and findings presented contribute to improved reservoir characterization and predictive modeling of sandstone formations.
