Ti5553-xFe (x=0.4, 1.2, 2.0, wt.%) alloys have been designed and fabricated through BE (blended element) sintering to investigate the effect of Fe-addition on athermal ω-phase transformation, α-phase evolution and a...Ti5553-xFe (x=0.4, 1.2, 2.0, wt.%) alloys have been designed and fabricated through BE (blended element) sintering to investigate the effect of Fe-addition on athermal ω-phase transformation, α-phase evolution and age hardening behavior. The results show that the formation of athermal ω-phase is fully suppressed in water-quenched specimens when Fe-addition is up to 2 wt.%. The relevant timescales of α formation during initial stages of aging indicate that incubation time increases with Fe-addition. Further aging results in continuous nucleation and growth of α-phase but finer intragranular α lamellae exhibit in Ti5553-2Fe alloy. In addition, the width and extent of grain boundary α-film increase slightly with incremental Fe-addition, especially in furnace cooling condition. Result of Vickers hardness manifests that Fe-addition leads to a strong hardening effect in both solution and aging treatment. The solid solution strengthening is quantitatively estimated by ab initio calculation based on the Labusch?Nabarro model. The evolution of α-precipitate is rationalized by Gibbs free energy. The prominent hardening effect of Ti5553?2Fe alloy is attributed to both large lattice misfit of β-matrix and fine α-precipitate distribution.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
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
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
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
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
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
Biochar,a solid carbonaceous material produced by heating biomass in oxygen-free or low-oxygen conditions(pyrolysis),has been used in various applications,including wastewater treatment,carbon sequestration,and improv...Biochar,a solid carbonaceous material produced by heating biomass in oxygen-free or low-oxygen conditions(pyrolysis),has been used in various applications,including wastewater treatment,carbon sequestration,and improving soil fertility.However,very limited research has been performed to explore its feasibility to improve the expansive clay(EC)subgrade.In this study,fine-grained wood biochar derived from wood waste was used to stabilise and enhance the mechanical performance of the EC as road subgrade.A comprehensive series of geotechnical tests,including unconfined compressive strength(UCS),California bearing ratio(CBR),repeated load triaxial(RLT),and swelling-shrinkage tests,were conducted to investigate the engineering properties of expansive clay mixed with different contents of the fine-grained biochar(FGB)(i.e.0,1%,2%,3%,and 4%by weight of dry soil).Furthermore,X-ray diffraction(XRD),X-ray fluorescence(XRF),X-ray micro-CT,and thermogravimetric analysis(TGA)analyses were performed to study the microchemical modification of the EC-FGB mixtures.The results showed that adding FGB reduced the swelling and shrinkage potential while enhancing the mechanical properties of the EC.The micro-level analysis also supported the enhancement of the geotechnical performance of the EC resulting from the incorporation of FGB.According to the test results,2%FGB was considered the optimum content,increasing UCS,CBR,and resilient modulus by 31.1%,24.1%,and 31.5%,respectively,and decreasing the swell-shrinkage index by 7%.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
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
In order to explore the mechanical properties and microstructure changes of frozen saline silty clay in the Hexi region of Gansu Province,triaxial compression tests and scanning electron microscopy(SEM)analysis experi...In order to explore the mechanical properties and microstructure changes of frozen saline silty clay in the Hexi region of Gansu Province,triaxial compression tests and scanning electron microscopy(SEM)analysis experiment were conducted to explore the effects of moisture content,confining pressure,and temperature on the stress-strain characteristics and failure modes of frozen soil,as well as the changes in the internal microstructure of the sample.The experimental results show that the strength of frozen sulfate saline soil first increases and then decreases with the increase of moisture content,and the maximum strength corresponds to a moisture content of 15%.The changes in confining pressure and strength have the same trend.The lower the temperature,the greater the strength of the sample.During the entire loading process,the specimens undergo a gradual transition from volume shrinkage to volume expansion.Due to the strain harden behavior of the stress-strain curve throughout the entire loading process,the failure mode of the specimens is plastic failure.The internal microstructure of the sample gradually transitions from point-point contact and edge-point contact before shearing to edge-surface contact and edge-edge contact after shearing,and the pore size inside the sample increases after shearing,with a loose arrangement of the particle skeleton.The above research conclusions can lay a certain theoretical foun-dation for the engineering design and construction of sulfate saline soil in cold and arid areas.展开更多
This study was part of the framework that contributed not only to the improvement of thermal comfort in housing but also to the decarbonization of the construction and building materials industry. For this purpose, te...This study was part of the framework that contributed not only to the improvement of thermal comfort in housing but also to the decarbonization of the construction and building materials industry. For this purpose, terracotta brick seems to meet these needs. Thus, the objective of this work was to evaluate the influence of the incorporation of coal fly ash from a thermal power plant on the physical and mechanical properties of fired bricks from grey clay in the Thicky area of Senegal. The coal fly ash was incorporated into the raw clay material in proportions of 0, 5, 10, and 15 % by weight. These two raw materials were first characterized by X-ray fluorescence spectroscopy (XRF). The XRF analyses showed that the most abundant oxides in clay were SiO2 (55.034%) and Fe2O3 (10.155%). In coal fly ash, SiO2 (38.574%) is predominant. The ash also contained Al2O3 (7.717%) and alicano-earthy melting oxides such as CaO (9.271%) and MgO (7.298%) etc. These melting oxides were necessary to facilitate the formation of the liquid phase when baking platelets. The latter, when burned at a temperature of 880°C, were characterized by determining the number of physico-mechanical parameters, such as linear shrinkage during cooking, water absorption, fire loss and compressive strength. A Hierarchical Ascending Classification of these different parameters was performed and three classes were obtained. Class 1 with better compressive strength (6.358 MPa), was in sample A (5%). Class 2 consisted of sample D (reference) and had a higher plasticity index (28.51%) and water absorption rate (11.19%). Finally, class 3, which included samples B (10%) and C (15%), had very high shrinkage and fire losses compared to other platelets. These results highlighted the possibility of using up to 5% of the coal fly ash in the production of new fired bricks with good performance.展开更多
Cement production,while essential for global infrastructure,contributes significantly to carbon dioxide emissions,accounting for approximately 7%of total emissions.To mitigate these environmental impacts,flash calcina...Cement production,while essential for global infrastructure,contributes significantly to carbon dioxide emissions,accounting for approximately 7%of total emissions.To mitigate these environmental impacts,flash calcination of kaolinitic clays has been investigated as a sustainable alternative.This technique involves the rapid heating of clays,enabling their use as supplementary cementitious materials.The primary objective of this study was to modify the color of calcined clay in various atmospheres(oxidizing,inert,and reducing)to achieve a grayish tone similar to commercial cement while preserving its reactive properties.The experimental procedure employed a tubular reactor with precise control of gas flows(atmospheric air,nitrogen,and a carbon monoxide–nitrogen mixture).Physicochemical characterization of the raw clay was conducted before calcination,with analyses repeated on the calcined clays following experimentation.Results indicated that clay calcined in an oxidizing atmosphere acquired a reddish hue,attributed to the oxidation of iron in hematite.The Clay exhibited a pinkish tone in an inert atmosphere,while calcination in a reducing atmosphere yielded the desired grayish color.Regarding pozzolanic activity,clays calcined in oxidizing and inert atmospheres displayed robust strength,ranging from 82%to 87%.Calcination in a reducing atmosphere resulted in slightly lower strength,around 74%,likely due to the clay’s chemical composition and the calcination process,which affects compound formation and material reactivity.展开更多
Urban spaces are becoming increasingly congested,and excavations are frequently performed close to existing underground structures such as tunnels.Understanding the mechanical response of proximal soil and tunnels to ...Urban spaces are becoming increasingly congested,and excavations are frequently performed close to existing underground structures such as tunnels.Understanding the mechanical response of proximal soil and tunnels to these excavations is important for efficient and safe underground construction.However,previous investigations of this issue have predominantly made assumptions of plane-strain conditions and normal gravity states,and focused on the performance of tunnels affected by excavation and unloading in sandy strata.In this study,a 3D centrifuge model test is conducted to investigate the influence of excavation on an adjacent existing tunnel in normally consolidated clay.The testing results indicate that the excavation has a significant impact on the horizontal deformation of the retaining wall and tunnel.Moreover,the settlements of the ground surface and the tunnel are mainly affected by the long-term period after excavation.The excavation is found to induce ground movement towards the pit,resulting in prolonged fluctuations in pore water pressure and lateral earth pressure.The testing results are compared with numerical simulations,achieving consistency.A numerical parametric study on the tunnel location shows that when the tunnel is closer to the retaining wall,the decreases in lateral earth pressure and pore water pressure during excavation are more pronounced.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
Geosynthetic-encased stone column(GESC)technology for strengthening soft clay offers significant advantages in terms of cost-effectiveness,environmental sustainability,and engineering applicability.It is widely applie...Geosynthetic-encased stone column(GESC)technology for strengthening soft clay offers significant advantages in terms of cost-effectiveness,environmental sustainability,and engineering applicability.It is widely applied in treating soft foundations for railways,bridges,and embankments.This study evaluates the cyclic response of the geosynthetic-encased steel slag column(GESSC)composite foundation employing three-dimensional nonlinear finite element analysis.A numerical study is conducted to assess the cyclic response of floating GESSC considering the influence of key design variables,including cyclic load amplitude,loading frequency,geosynthetic encasement stiffness,and length-to-diameter ratio.Results show that both cyclic load amplitude and frequency affect the cumulative settlement and excess pore pressure within the GESSC foundation.Within specified limits,increasing the encasement stiffness and column length can significantly improve the GESSC load-bearing characteristics.The parametric study suggests an optimal geosynthetic encasement stiffness for the field prototype columns within the range of 4480–5760 kN/m and a critical steel slag column length of 10 times the column diameter.展开更多
The traditional cement-based stabilization cannot effectively stabilize the marine soft clay under submerged conditions.In order to solve this problem,the enhancement of cement-stabilized marine soft clay was investig...The traditional cement-based stabilization cannot effectively stabilize the marine soft clay under submerged conditions.In order to solve this problem,the enhancement of cement-stabilized marine soft clay was investigated in this study by adding the ionic soil stabilizer(ISS)and polyacrylamide(PAM).For this purpose,varying contents of ISS and PAM(ISS-P)were added into cement-stabilized marine soft clay and subjected to curing under submerged conditions.Atterberg limits tests,direct shear tests,unconfined compression strength(UCS)tests,water-stability tests,scanning electron microscopy analysis,and X-ray diffraction analysis were carried out.The results show that using 1.8%ISS and 0.9%PAM as the optimal ratio,the cohesion,internal friction angle,UCS,and water-stability of the samples increased by 182.7%,15.4%,176.5%,and 368.5% compared to the cement-stabilized soft clay after 28 d.The increment in soil cohesion with increasing ISS-P content was more apparent than that in the internal friction angle.The combined action of ion exchange attraction and electrostatic adsorption altered the failure characteristics of the samples,resulting in localized micro-cracking and multiple failure paths.Increasing the content of ISS-P strengthened the skeletal structure of soil,reduced inter-particle spacing,and enhanced the water-stability.Additionally,ISS promotes the hydration of cement and compensates for the inhibitory effect of PAM on early cement hydration.ISS-P can effectively enhance the strength and stability of submerged cement-based stabilized marine soft clay.展开更多
Fissured clays exhibit unique geotechnical behaviors,with the stiffness characteristics evolving dynamically in response to environmental changes.To address this issue,reported here is a systematic assessment of how d...Fissured clays exhibit unique geotechnical behaviors,with the stiffness characteristics evolving dynamically in response to environmental changes.To address this issue,reported here is a systematic assessment of how dryingewetting(DW)cycles affect the small-strain stiffness characteristics of fissured clay.Resonant column tests are taken to examine the nonlinear attenuation behavior of the small-strain shear modulus(SSSM)and damping ratio of fissured clay under various DW cycle and consolidation pressure(25e200 kPa)conditions.Scanning electron microscopy(SEM)and computed tomography(CT)are employed to reveal the microstructure of fissured clay.The HardineDrnevich(H-D)model is used to describe the decay law of its SSSM,and the small strain stiffness characteristics of fissured soil are analyzed in view of damage mechanics.The results show that the SSSM of the fissured clay decreases as the DWcycles increase,with the greatest attenuation at original soil state.The damping ratio exhibits an incremental trend with escalating strain and a higher number of DW cycles.Regarding damage,DW cycles can lead to the formation of microcracks in the sample,and the aggregates disperse into smaller aggregates,which then aggregates again,resulting in structural damage.The damage variables of the samples under various confining pressures and DW cycles are analyzed based on the principle of strain damage.Finally,the volume changes and the distribution of different pore sizes obtained through CT are analyzed to investigate the stiffness attenuation under DW cycles.Additionally,the study examines the propagation direction of secondary cracks induced by primary fissures,which will play an important role in reduction of the stiffness.Our investigations contribute to understanding of soil mechanics and practical applications in areas where fissured clay is prevalent.展开更多
Red clay,widely used as a subgrade material in southern China,requires a reliable evaluation of its dynamic behavior to ensure infrastructure safety.Long-term cyclic triaxial tests were conducted on red clay from typi...Red clay,widely used as a subgrade material in southern China,requires a reliable evaluation of its dynamic behavior to ensure infrastructure safety.Long-term cyclic triaxial tests were conducted on red clay from typical,complex subway subgrades to investigate its dynamic properties and shakedown behavior under intermittent cyclic loading.Results show that intermittent cyclic loading,especially with multiple amplitudes,causes greater axial plastic strain and lower post-cyclic strength than continuous loading.These effects diminish with increasing confining pressure.Notably,axial strain partially recovers during loading intervals,with recovery ratios depending on the number and sequence of pauses.Based on the rules of cumulative plastic strain rates and cumulative plastic strain increments,shakedown behavior for red clay under intermittent cyclic loading is divided into three categories:plastic shakedown,critical shakedown,and plastic creep.A quantitative shakedown limit criterion is proposed using the Boltzmann function.Shakedown behavior significantly influences the post-cyclic strengths,and the influence diminishes as confining pressure increases.Samples exhibiting plastic creep and plastic shakedown behavior have the lowest and highest strengths,and those with critical shakedown behaviors have medium strengths.Cyclic loading with relatively low-stress amplitude causes a hardening effect,while cyclic loading intermittence or cyclic loading with relatively high-stress amplitude causes a degradation effect,and both effects are mitigated by higher confining pressures.展开更多
基金Projects(51671158,51871176,51621063)supported by the National Natural Science Foundation of ChinaProject(2014CB644003)supported by the National Basic Research Program of China+1 种基金Project(PB2018008)supported by the 111 Project 2.0,ChinaProject(2018JM5098)supported by the Natural Science Basic Research Plan in Shaanxi Province of China
文摘Ti5553-xFe (x=0.4, 1.2, 2.0, wt.%) alloys have been designed and fabricated through BE (blended element) sintering to investigate the effect of Fe-addition on athermal ω-phase transformation, α-phase evolution and age hardening behavior. The results show that the formation of athermal ω-phase is fully suppressed in water-quenched specimens when Fe-addition is up to 2 wt.%. The relevant timescales of α formation during initial stages of aging indicate that incubation time increases with Fe-addition. Further aging results in continuous nucleation and growth of α-phase but finer intragranular α lamellae exhibit in Ti5553-2Fe alloy. In addition, the width and extent of grain boundary α-film increase slightly with incremental Fe-addition, especially in furnace cooling condition. Result of Vickers hardness manifests that Fe-addition leads to a strong hardening effect in both solution and aging treatment. The solid solution strengthening is quantitatively estimated by ab initio calculation based on the Labusch?Nabarro model. The evolution of α-precipitate is rationalized by Gibbs free energy. The prominent hardening effect of Ti5553?2Fe alloy is attributed to both large lattice misfit of β-matrix and fine α-precipitate distribution.
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.
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 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.
基金supported by the Australian Research Council Training Centre for Whole Life Design of Carbon Neutral Infrastructure(Grant No.IC230100015).
文摘Biochar,a solid carbonaceous material produced by heating biomass in oxygen-free or low-oxygen conditions(pyrolysis),has been used in various applications,including wastewater treatment,carbon sequestration,and improving soil fertility.However,very limited research has been performed to explore its feasibility to improve the expansive clay(EC)subgrade.In this study,fine-grained wood biochar derived from wood waste was used to stabilise and enhance the mechanical performance of the EC as road subgrade.A comprehensive series of geotechnical tests,including unconfined compressive strength(UCS),California bearing ratio(CBR),repeated load triaxial(RLT),and swelling-shrinkage tests,were conducted to investigate the engineering properties of expansive clay mixed with different contents of the fine-grained biochar(FGB)(i.e.0,1%,2%,3%,and 4%by weight of dry soil).Furthermore,X-ray diffraction(XRD),X-ray fluorescence(XRF),X-ray micro-CT,and thermogravimetric analysis(TGA)analyses were performed to study the microchemical modification of the EC-FGB mixtures.The results showed that adding FGB reduced the swelling and shrinkage potential while enhancing the mechanical properties of the EC.The micro-level analysis also supported the enhancement of the geotechnical performance of the EC resulting from the incorporation of FGB.According to the test results,2%FGB was considered the optimum content,increasing UCS,CBR,and resilient modulus by 31.1%,24.1%,and 31.5%,respectively,and decreasing the swell-shrinkage index by 7%.
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 National Natural Science Foun-dation of China(12362032)the Key Research and Development Pro-gram of Gansu Province-Social Development(23YFFA0063).
文摘In order to explore the mechanical properties and microstructure changes of frozen saline silty clay in the Hexi region of Gansu Province,triaxial compression tests and scanning electron microscopy(SEM)analysis experiment were conducted to explore the effects of moisture content,confining pressure,and temperature on the stress-strain characteristics and failure modes of frozen soil,as well as the changes in the internal microstructure of the sample.The experimental results show that the strength of frozen sulfate saline soil first increases and then decreases with the increase of moisture content,and the maximum strength corresponds to a moisture content of 15%.The changes in confining pressure and strength have the same trend.The lower the temperature,the greater the strength of the sample.During the entire loading process,the specimens undergo a gradual transition from volume shrinkage to volume expansion.Due to the strain harden behavior of the stress-strain curve throughout the entire loading process,the failure mode of the specimens is plastic failure.The internal microstructure of the sample gradually transitions from point-point contact and edge-point contact before shearing to edge-surface contact and edge-edge contact after shearing,and the pore size inside the sample increases after shearing,with a loose arrangement of the particle skeleton.The above research conclusions can lay a certain theoretical foun-dation for the engineering design and construction of sulfate saline soil in cold and arid areas.
文摘This study was part of the framework that contributed not only to the improvement of thermal comfort in housing but also to the decarbonization of the construction and building materials industry. For this purpose, terracotta brick seems to meet these needs. Thus, the objective of this work was to evaluate the influence of the incorporation of coal fly ash from a thermal power plant on the physical and mechanical properties of fired bricks from grey clay in the Thicky area of Senegal. The coal fly ash was incorporated into the raw clay material in proportions of 0, 5, 10, and 15 % by weight. These two raw materials were first characterized by X-ray fluorescence spectroscopy (XRF). The XRF analyses showed that the most abundant oxides in clay were SiO2 (55.034%) and Fe2O3 (10.155%). In coal fly ash, SiO2 (38.574%) is predominant. The ash also contained Al2O3 (7.717%) and alicano-earthy melting oxides such as CaO (9.271%) and MgO (7.298%) etc. These melting oxides were necessary to facilitate the formation of the liquid phase when baking platelets. The latter, when burned at a temperature of 880°C, were characterized by determining the number of physico-mechanical parameters, such as linear shrinkage during cooking, water absorption, fire loss and compressive strength. A Hierarchical Ascending Classification of these different parameters was performed and three classes were obtained. Class 1 with better compressive strength (6.358 MPa), was in sample A (5%). Class 2 consisted of sample D (reference) and had a higher plasticity index (28.51%) and water absorption rate (11.19%). Finally, class 3, which included samples B (10%) and C (15%), had very high shrinkage and fire losses compared to other platelets. These results highlighted the possibility of using up to 5% of the coal fly ash in the production of new fired bricks with good performance.
基金financial support for the research and for the publication costs of the articlesupported by Santa Catarina State Research Support Foundation(FAPESC)National Council for Scientific and Technological Development(CNPq no 302903/2023-2).
文摘Cement production,while essential for global infrastructure,contributes significantly to carbon dioxide emissions,accounting for approximately 7%of total emissions.To mitigate these environmental impacts,flash calcination of kaolinitic clays has been investigated as a sustainable alternative.This technique involves the rapid heating of clays,enabling their use as supplementary cementitious materials.The primary objective of this study was to modify the color of calcined clay in various atmospheres(oxidizing,inert,and reducing)to achieve a grayish tone similar to commercial cement while preserving its reactive properties.The experimental procedure employed a tubular reactor with precise control of gas flows(atmospheric air,nitrogen,and a carbon monoxide–nitrogen mixture).Physicochemical characterization of the raw clay was conducted before calcination,with analyses repeated on the calcined clays following experimentation.Results indicated that clay calcined in an oxidizing atmosphere acquired a reddish hue,attributed to the oxidation of iron in hematite.The Clay exhibited a pinkish tone in an inert atmosphere,while calcination in a reducing atmosphere yielded the desired grayish color.Regarding pozzolanic activity,clays calcined in oxidizing and inert atmospheres displayed robust strength,ranging from 82%to 87%.Calcination in a reducing atmosphere resulted in slightly lower strength,around 74%,likely due to the clay’s chemical composition and the calcination process,which affects compound formation and material reactivity.
基金supported by the National Natural Science Foundation of China(Nos.52378341,51938005,and 52090082).
文摘Urban spaces are becoming increasingly congested,and excavations are frequently performed close to existing underground structures such as tunnels.Understanding the mechanical response of proximal soil and tunnels to these excavations is important for efficient and safe underground construction.However,previous investigations of this issue have predominantly made assumptions of plane-strain conditions and normal gravity states,and focused on the performance of tunnels affected by excavation and unloading in sandy strata.In this study,a 3D centrifuge model test is conducted to investigate the influence of excavation on an adjacent existing tunnel in normally consolidated clay.The testing results indicate that the excavation has a significant impact on the horizontal deformation of the retaining wall and tunnel.Moreover,the settlements of the ground surface and the tunnel are mainly affected by the long-term period after excavation.The excavation is found to induce ground movement towards the pit,resulting in prolonged fluctuations in pore water pressure and lateral earth pressure.The testing results are compared with numerical simulations,achieving consistency.A numerical parametric study on the tunnel location shows that when the tunnel is closer to the retaining wall,the decreases in lateral earth pressure and pore water pressure during excavation are more pronounced.
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.
基金support from the National Natural Science Foundation of China(Grant Nos.52078427 and 51608461)is greatly acknowledged.
文摘Geosynthetic-encased stone column(GESC)technology for strengthening soft clay offers significant advantages in terms of cost-effectiveness,environmental sustainability,and engineering applicability.It is widely applied in treating soft foundations for railways,bridges,and embankments.This study evaluates the cyclic response of the geosynthetic-encased steel slag column(GESSC)composite foundation employing three-dimensional nonlinear finite element analysis.A numerical study is conducted to assess the cyclic response of floating GESSC considering the influence of key design variables,including cyclic load amplitude,loading frequency,geosynthetic encasement stiffness,and length-to-diameter ratio.Results show that both cyclic load amplitude and frequency affect the cumulative settlement and excess pore pressure within the GESSC foundation.Within specified limits,increasing the encasement stiffness and column length can significantly improve the GESSC load-bearing characteristics.The parametric study suggests an optimal geosynthetic encasement stiffness for the field prototype columns within the range of 4480–5760 kN/m and a critical steel slag column length of 10 times the column diameter.
基金supported by the Fundamental Research Funds for the Central Universities(Nos.202061027,202261063)the National Natural Science Foundation of China(No.41572247)。
文摘The traditional cement-based stabilization cannot effectively stabilize the marine soft clay under submerged conditions.In order to solve this problem,the enhancement of cement-stabilized marine soft clay was investigated in this study by adding the ionic soil stabilizer(ISS)and polyacrylamide(PAM).For this purpose,varying contents of ISS and PAM(ISS-P)were added into cement-stabilized marine soft clay and subjected to curing under submerged conditions.Atterberg limits tests,direct shear tests,unconfined compression strength(UCS)tests,water-stability tests,scanning electron microscopy analysis,and X-ray diffraction analysis were carried out.The results show that using 1.8%ISS and 0.9%PAM as the optimal ratio,the cohesion,internal friction angle,UCS,and water-stability of the samples increased by 182.7%,15.4%,176.5%,and 368.5% compared to the cement-stabilized soft clay after 28 d.The increment in soil cohesion with increasing ISS-P content was more apparent than that in the internal friction angle.The combined action of ion exchange attraction and electrostatic adsorption altered the failure characteristics of the samples,resulting in localized micro-cracking and multiple failure paths.Increasing the content of ISS-P strengthened the skeletal structure of soil,reduced inter-particle spacing,and enhanced the water-stability.Additionally,ISS promotes the hydration of cement and compensates for the inhibitory effect of PAM on early cement hydration.ISS-P can effectively enhance the strength and stability of submerged cement-based stabilized marine soft clay.
基金the financial support of the National Key Research and Development Program of China(Grant No.2019YFC1509901).
文摘Fissured clays exhibit unique geotechnical behaviors,with the stiffness characteristics evolving dynamically in response to environmental changes.To address this issue,reported here is a systematic assessment of how dryingewetting(DW)cycles affect the small-strain stiffness characteristics of fissured clay.Resonant column tests are taken to examine the nonlinear attenuation behavior of the small-strain shear modulus(SSSM)and damping ratio of fissured clay under various DW cycle and consolidation pressure(25e200 kPa)conditions.Scanning electron microscopy(SEM)and computed tomography(CT)are employed to reveal the microstructure of fissured clay.The HardineDrnevich(H-D)model is used to describe the decay law of its SSSM,and the small strain stiffness characteristics of fissured soil are analyzed in view of damage mechanics.The results show that the SSSM of the fissured clay decreases as the DWcycles increase,with the greatest attenuation at original soil state.The damping ratio exhibits an incremental trend with escalating strain and a higher number of DW cycles.Regarding damage,DW cycles can lead to the formation of microcracks in the sample,and the aggregates disperse into smaller aggregates,which then aggregates again,resulting in structural damage.The damage variables of the samples under various confining pressures and DW cycles are analyzed based on the principle of strain damage.Finally,the volume changes and the distribution of different pore sizes obtained through CT are analyzed to investigate the stiffness attenuation under DW cycles.Additionally,the study examines the propagation direction of secondary cracks induced by primary fissures,which will play an important role in reduction of the stiffness.Our investigations contribute to understanding of soil mechanics and practical applications in areas where fissured clay is prevalent.
基金the support of the National Natural Science Foundation of China(Grant No.52108319)the Natural Science Foundation of Jiangxi Province(20224BAB214069)。
文摘Red clay,widely used as a subgrade material in southern China,requires a reliable evaluation of its dynamic behavior to ensure infrastructure safety.Long-term cyclic triaxial tests were conducted on red clay from typical,complex subway subgrades to investigate its dynamic properties and shakedown behavior under intermittent cyclic loading.Results show that intermittent cyclic loading,especially with multiple amplitudes,causes greater axial plastic strain and lower post-cyclic strength than continuous loading.These effects diminish with increasing confining pressure.Notably,axial strain partially recovers during loading intervals,with recovery ratios depending on the number and sequence of pauses.Based on the rules of cumulative plastic strain rates and cumulative plastic strain increments,shakedown behavior for red clay under intermittent cyclic loading is divided into three categories:plastic shakedown,critical shakedown,and plastic creep.A quantitative shakedown limit criterion is proposed using the Boltzmann function.Shakedown behavior significantly influences the post-cyclic strengths,and the influence diminishes as confining pressure increases.Samples exhibiting plastic creep and plastic shakedown behavior have the lowest and highest strengths,and those with critical shakedown behaviors have medium strengths.Cyclic loading with relatively low-stress amplitude causes a hardening effect,while cyclic loading intermittence or cyclic loading with relatively high-stress amplitude causes a degradation effect,and both effects are mitigated by higher confining pressures.
