Pore Fluid Chemistry Research Articles

A Theoretical Model for the Hydraulic Permeability of Clayey Sediments Considering the Impact of Pore Fluid Chemistry

The chemistry of the pore fluid within clayey sediments frequently changes in various processes. However, the impacts of pore fluid chemistry have not been well included in the hydraulic permeability model, and the physical bases behind the salinity sensitivity of the hydraulic permeability remains elusive. In this study, a theoretical model for the hydraulic permeability of clayey sediments is proposed, and impacts of the pore fluid chemistry are quantitatively considered by introducing electrokinetic flow theory. Available experimental data were used to verify the theoretical model, and the verified model was further applied as a sensitivity analysis tool to explore more deeply how hydraulic permeability depends on pore fluid chemistry under different conditions. Coupling effects of pore water desalination and the effective stress enhancement on the hydraulic permeability of marine sediments surrounding a depressurization wellbore during hydrate production are discussed. Results and discussion show that the hydraulic permeability reduction is significant only when the electric double layer thickness is comparable to the characteristic pore size, and the reduction becomes more obvious when the ion mobility of the saline solution is smaller and the surface dielectric potential of clay minerals is lower. During gas hydrate production in the ocean, the salinity sensitivity of the hydraulic permeability could become either stronger and weaker, depending on whether the original characteristic pore size of marine sediments is relatively large or small.

Biotic and abiotic processes in Ediacaran spheroid formation

Organic-rich shales from the uppermost Doushantuo Fm. (South China) record one of the most negative carbonate carbon isotopic excursions in Earth’s history, known as the Shuram excursion, and contain meter to micro-size spheroids. In this study, we use Raman and energy dispersive spectroscopy to identify and describe the most common diagenetic spheroids to refine our understanding of the profound perturbations of the carbon cycle and the evolution of pore fluid chemistry imprinted in the sedimentary Precambrian record, especially in the late Ediacaran. The presence of 13C-depleted carbonate concretions or organic matter (OM) enclosed by lenticular dolomitic structures within the host shale unit suggests OM remineralisation and anaerobic oxidation, resulting in authigenic carbonate precipitation during the earliest stages of sediment diagenesis. Other mineralogical features, however, point to high levels of primary production, such as apatite bands that host spheroidal microfossils with highly fluorescent quartz and OM within abiotic concretions. These observations highlight the importance of considering co-occurring biotic and abiotic processes in explaining the formation of diagenetic spheroids in ancient sedimentary environments. From an astrobiology perspective, the interplay of biotic and abiotic processes reflects the complexity of early life systems and the environments that may exist on other terrestrial planets. Understanding the signatures of biotic and abiotic interactions in the Doushantuo Fm. is crucial for identifying potential biosignatures in extraterrestrial materials, thereby enhancing our understanding of life’s universality and adaptability in diverse and extreme environments.

Characterization of pore water microdynamics and microstructure of clays: The effect of pore fluid chemistry and temperature

It is crucial to figure out the microdynamics of pore water and the microstructure of clays under various thermal and chemical environments when characterizing the physical properties of clays. In this study water microdynamics in clay was investigated via the nuclear magnetic resonance (NMR) technique. The NMR measurements were performed on three clays saturated with distilled water and three salt solutions from 25 to 75°C. The saline and thermal effect on soil-water interaction, water microdynamics and microstructure of clays has been investigated through relaxation times by invoking the DDL theory and the ionic hydration mechanism. Number of jumps (τS/τm) for water molecule is 82 for soils A or C and 520 for soil B when saturated with distilled water, implying the larger surface molecular affinity of soil B. Salt solutions increase the values of τS/τm in the sequence of K+>Ca2+>Na+. Effective activation energy of pore waterΔE= 2.33 kcal/mol, 1.49 kcal/mol and 1.19 kcal/mol for soils A, B and C when saturated with distilled water are obtained. The effect of salt solution on ΔE depends on cation exchange capacity (CEC) and specific surface area (SSA), the larger the CEC and SSA, the smaller the saline effect. In addition, it is found that the pore size distribution of the compacted clay is bimodal, and inter-aggregate pores are greatly influenced by pore fluid chemistry, due to clay aggregation.

A process-based geochemical framework for carbonate sediments during marine diagenesis

A significant proportion of marine calcium carbonate sediments are comprised of metastable minerals that are susceptible to diagenetic alterations during burial. These reactions can reset the geochemical signature of sediments and pore fluids and influence elemental cycling in the ocean. However, the timing and mechanisms by which these reactions take place are poorly constrained. This study uses cores drilled on the slope of the Great Bahama Bank to provide quantitative constraints on important diagenetic reactions; namely respiration-driven dissolution, authigenic carbonate mineral formation, and conversion of aragonite to low Mg calcite (LMC). We perform detailed mineralogical characterization using newly acquired, high resolution X-ray diffraction (XRD) data and over 1000 reanalyzed XRD scans, characterize sediments texturally and elementally using electron microprobe data, calculate pore fluid saturation state with respect to aragonite using a Pitzer ion interaction approach, and use pore fluid chemistry and experimental distribution coefficients to predict authigenic carbonate compositions. These data suggest that aerobic organic matter oxidation, enabled by the advection of oxygenated seawater throughout the upper ∼ 30 m interval of sediment, causes undersaturation and thus dissolution of biogenic high Mg calcite (HMC) and aragonite. Deeper, anaerobic organic matter oxidation takes over and causes supersaturation, promoting authigenic precipitation in the form of HMC, which in turn decreases pore fluid Mg/Ca and promotes aragonite conversion to LMC. One novel aspect of this study is the identification of three types of calcites using the newly acquired XRD and electron microprobe data. Based on their unique crystallographic characteristics and chemical compositions, these types of calcites are interpreted to represent pelagic biogenic LMC, bank-derived biogenic HMC, and authigenic HMC precipitated from pore fluids. Notably, the composition of the authigenic calcite matches that predicted to precipitate from pore fluids using an empirical Mg partition coefficient in calcite. Calcites that form authigenically and from aragonite via replacement are suggested to recrystallize with burial as evidenced by the decrease in Mg content and micro-strain. This process-based geochemical framework assigns diagenetic processes to a specific depth window within the sediment column and paves the way for a mechanistic understanding of carbonate diagenesis, one that is rooted in thermodynamic and kinetic bases.

Geochemical indications of hydrothermal fluid through sediments within the Geolin Mounds and Mienhua Volcano hydrothermal fields, southernmost Okinawa Trough

This study focused on the chemistry of sedimentary pore fluids to clarify hydrothermal fluid migrating within sediments at the Geolin Mounds (GLM) and Mienhua Volcano (MHV) hydrothermal fields, southernmost Okinawa Trough, where are characterized by covering of thick sediment. The significant downward decrease in Mg2+ (low to 23.3 mmol L−1) and concurrent increase in Li+ (up to 2,269 μmol L−1) in sedimentary pore fluids implied a substantial influence of hydrothermal fluid, which might be associated with high-temperature (>350 °C) rock/sediment-fluid interaction. The best fitting of the 1-D advection-diffusion equation to pore-fluid Cl−, Mg2+, and Li+ concentrations further evidenced the upward hydrothermal through sediments with rates of 0.13 ∼ 124 cm yr−1. The apparently Cl-depleted and slightly Cl-enriched pore fluids in the GLM and MHV hydrothermal fields supported the occurrence of subseafloor phase separation and classified their hydrothermal fluids into vapor-rich and brine-rich phases, respectively. The low pH values (pH = 5.67 ∼ 6.21) with downward increasing trends of pore-fluid dissolved inorganic carbon (DIC, up to 60 mmol L−1) and its heavy isotopic compositions (δ13CDIC = +2.5 ∼ +7.0 ‰) inferred in-situ liquid CO2-impregnated sedimentary circumstance in the GLM and MHV hydrothermal fields. This sedimentary environment, as demonstrated, enhanced the chemical weathering of silicate and carbonate minerals, resulting in the elevated concentrations of Ca2+ and K+ in pore fluids. It highlights the impact of acidic and in-situ CO2-saturated fluids within sediments on geochemical alterations of bulk solids/sediments and interstitial fluids.

THEORETICAL FRAMEWORK FOR LARGE-STRAIN SHEAR RESISTANCE OF KAOLIN CLAYS UNDER CHEMO-MECHANICAL LOADINGS

The normal stress, strain rate, and pore-fluid chemistry significantly influence the large-strain shear response of clays and received great attention for engineering practice. The effect of inundation pressure, consolidation pressure, pH of aqueous solutions, and di-electric on the shear response of kaolin was experimentally investigated. The strain-softening behaviour was observed under normally consolidated (NC) conditions as observed in the past studies on different clays. However, this anomalous shear response with volumetric contraction is not understood. Thus, for the first time, the strain-softening behaviour of NC clays was addressed from an effective stress approach using physico-chemical analysis of kaolin. In this study, the drained shear strength response of NC kaolin was investigated under physico-chemical influence using ring shear tests. A theoretical framework was developed by including micro-mechanism of clay fabric evolution during shear and explicit expressions for electro-chemical forces. The proposed framework provides useful expressions for predicting the shear strength behaviour of kaolin clays, which were validated with experimental data from the present study and literature studies. The new conceptual framework satisfactorily explained the peak and residual shear strength variations under different chemo-mechanical loading for NC conditions. The proposed model adequately predicted the effective stress paths, peak, and residual envelopes in ring shear stress conditions for normally consolidated kaolin soils

Clay micromechanics: Mapping the future of particle-scale modelling of clay

Geotechnical engineers need to predict the macroscopic behaviour of clays in terms of strength, stiffness, and permeability and the variation in these properties during deformation. Engineers also need to predict the influence of environmental variables (temperature, pressure, pore-fluid chemistry) on these engineering properties. Particle-based methods, which explicitly model individual clay platelets and their interactions, can help identify the fundamental mechanisms that govern the engineering behaviour. Virtual samples can be created, and simulations can consider application of mechanical loading or change in the environmental conditions to generate data on particle kinematics and interparticle interactions. Particlebased models can be used to simulate stress and strain paths that are not easy to reproduce in physical experiments. This approach to simulation also enables parametric studies to understand the sensitivity of the overall behaviour to various particle characteristics and the nature of the particle interactions. This contribution provides a review of the state-of-theart of existing particle-based models for clays, namely Discrete Element Method (DEM), Monte Carlo method (MC), and Molecular Dynamics (MD). The technical challenges, advantages, and disadvantages of each method for the simulation of clays are presented and discussed, together with the technical developments we would like to see over the next decade to realize the full potential of these modelling tools.

Effect of pore water chemistry on the ring shear behavior and the rate dependency of residual strength

The rate dependency of residual strength plays an important role in the selection of residual strength parameters to design the remediation works for reactivated landslides. In the literature, it is shown that the rate dependency of residual strength depends on some factors such as types of soil, range of shear rates, range of effective normal stresses, and pore water chemistry. Recently, the effect of pore water chemistry on the rate dependency of residual strength soil has been examined. However, the ring shear behavior and the rate dependency of residual strength of soil having different pore fluids should be more evaluated. In this study, the effect of the pore fluids of distilled water and 1 M NaCl on the rate dependency of residual strength of kaolin clay was investigated in the Bishop ring shear apparatus. The ring shear tests were conducted at different shearing rates from 0.02 mm/min to 20 mm/min under the effective normal stress of 98 kPa. The research results showed that the pore fluid chemistry affected the shear displacement required to reach the peak strength, the vertical displacement, and the peak strength of kaolin clay. These parameters also exhibited rate dependency, especially at the fast shear rates. The research also indicated that the pore fluid chemistry had a significant effect on the rate dependency of residual strength. Accordingly, the rate dependency of residual strength of kaolin mixed with distilled water showed a positive tendency while that of kaolin with 1 M NaCl as the pore fluid was the neutral tendency.

Numerical simulation of creep behavior of clay using discrete element method

The current study examined the creep behavior of clay in terms of particle sliding using samples containing montmorillonite and kaolinite by modeling all interparticle forces using the discrete element method. The effects of the stress level, pore fluid chemistry, fabric structure and mineral compositions of clay on creep behavior have been studied. The results show that creep mechanisms emerged as a result of clay particle slippage at their points of contact and deformation of the particles themselves. It was also observed that interparticle physicochemical interactions affected the creep behavior of clay minerals. Generally, the rate of secondary consolidation declined with an increase in loading due to densification of the soil. Additionally, a stronger DDL repulsive force led to the neutralization of applied stress at higher compressions, resulting in sooner completion of primary consolidation and initiation of creep.

Pore fluid chemistry effects on homogenization of compacted bentonite specimen with technological voids

Pore fluid chemistry effects on homogenization of compacted bentonite specimen with technological voids

Sedimentation Behavior of Clays in Response to Pore-Fluid Chemistry: Effect of Ionic Concentration and pH on Its Trends

This study investigates the effect of pore fluid chemistry on the sedimentation trends and liquid and plastic limits within the new fines classification framework for four clayey soils with different specific surface and mineralogy. The sedimentation tests and fall cone tests are performed with seven different ionic concentrations (c = 1 × 10−5 ∼ 1.8 M) and the four target pH values (pH = 3, 5, 7, and 9) for each of the ionic concentrations. Three different sedimentation trends such as flocculated, dispersed, and mixed (at c = 0.0015-to-0.003 M) modes are observed at different ion concentrations and pH conditions of the pore fluids. Three sedimentation parameters named A1, A2 and A3 are defined from the sedimentation curve. The relationship between them implies the salient features of the sedimentation trend for tested clayey soils. These parameters confirm the observed sedimentation modes and the critical ionic concentration; c* ∼ 3 × 10−3 M for AMK and EPK (high specific surface) and c* ∼ 1.5 × 10−3 M for LKW and MI (low specific surface) where notable fabric change occurs. The higher specific surface clays are classified as intermediate electrical sensitive clays whereas the lower specific surface clays are categorized into low electrical sensitivity fines in the new classification chart. A complementary data analysis for the sedimentation parameters and the new fines classification chart reveals that the robust link between distinct sedimentation trends and salient features of clay particles captured in the new fines classification chart can be useful to predict the sedimentation modes of clays with different pore fluid chemistry.

Reconstruction of the Diagenetic Environments of Tight Sandstone Reservoirs: A Case Study from the Tengger Formation in the Baiyinchagan Sag, Erlian Basin, Northern China

Abstract The Lower Cretaceous Tengger Formation located in the Baiyinchagan Sag of the Erlian Basin comprises mainly deeply buried tight sandstone. The identification of high-quality reservoirs in these thickly stacked and heterogeneous units requires a comprehensive understanding of the diagenetic environmental history of the rocks. This paper reports an integrated study involving thin-section petrography, scanning electron microscopy, X-ray diffraction, fluid-inclusion analysis, and vitrinite reflectance analysis of Tengger Formation sandstones with the aim of characterizing the diagenetic conditions of the reservoir rocks and providing guidance for future petroleum exploration. Observed mineral assemblages, the distribution of authigenic minerals, and the distribution and nature of pores suggest the presence of two types of diagenetic environment, acidic and alkaline, which have varied over time and vertically through the rock column. Acidic conditions are indicated by quartz overgrowths and dissolution of both feldspar and carbonate cement. In contrast, alkaline conditions are indicated by the precipitation of carbonate cement, feldspar overgrowths, quartz dissolution, and occurrences of authigenic illite and chlorite. Changes in pore fluid chemistry controlled the evolution of the diagenetic environment. The early diagenetic environment from 110 Ma to 107 Ma was syndepositional and thus controlled by the chemistry of water in depositional centers, which is interpreted to have been weakly alkaline. Significant burial that occurred at 107 Ma induced pulses of hydrothermal fluids and petroleum into the reservoir rocks, which caused a shift to an acidic diagenetic environment. From 103 Ma to 70 Ma, subsequent episodes of uplift and burial caused periodic alternation between acidic and alkaline diagenetic environments. Three distinct episodes of oil and gas charging interpreted from petrography and the homogenization temperatures of fluid inclusions played a critical role in the enhancement of porosity through time. From 70 Ma to the present, acidic diagenesis gradually weakened because of the consumption of organic acids during the process of interaction between rocks and fluids. This study demonstrates the importance of understanding the diagenetic history of reservoir rocks and provides the basis for improved reservoir characterization and optimized hydrocarbon exploration of the Tengger Formation.

Early-age characterisation of Portland cement by impedance spectroscopy

Alternating current impedance spectroscopy (ACIS) was used to assess the effect of different sand, anhydrite and water contents on the electrochemical response of Portland cement paste in the early stages of hydration. Potential factors that may affect impedance measurements and data interpretation are also discussed, such as the complexity of the chemical composition of cement, its physical properties and hydration kinetics, and technique limitations. The impedance data obtained were benchmarked against different supporting techniques and literature data, showing a strong relationship among hydration rates as determined by thermochemistry, setting time measurements by physical approaches, pore fluid chemistry, electrical conductivity and the observed impedance behaviour. The results demonstrate that ACIS is a sensitive technique for assessing cement paste hydration, enabling differentiation of changes in the water and cement content, hydration degree and microstructural development during the first 24 h after mixing.

Physicochemical effects of pore fluid on the dynamic behavior of reconstituted marine clay

An experimental investigation was conducted to study the effect of pore fluid chemistry on the dynamic behavior of reconstituted marine clay. Sodium chloride solution of 0.4 M and 1 M concentrations was used to induce the physicochemical changes. Strain-controlled undrained cyclic triaxial tests were carried out to evaluate the most important parameters such as shear modulus and damping ratio at a large strain range. The results showed that the effect of pore fluid was more pronounced on cyclic shear modulus values at a strain amplitude of 0.3–1%. Tests were also conducted to study the effect of physicochemical factors on the degradation of normalized modulus G N/G 1 of marine clay specimens reconstituted with distilled water and salt solutions.

Impact of High Methane Flux on the Properties of Pore Fluid and Methane-Derived Authigenic Carbonate in the ARAON Mounds, Chukchi Sea

We investigated the pore fluid and methane-derived authigenic carbonate (MDAC) chemistry from the ARAON Mounds in the Chukchi Sea to reveal how methane (CH4) seepage impacts their compositional and isotopic properties. During the ARA07C and ARA09C Expeditions, many in situ gas hydrates (GHs) and MDACs were found near the seafloor. The fluid chemistry has been considerably modified in association with the high CH4 flux and its related byproducts (GHs and MDACs). Compared to Site ARA09C-St 08 (reference site), which displays a linear SO42- downcore profile, the other sites (e.g., ARA07C-St 13, ARA07C-St 14, ARA09C-St 04, ARA09C-St 07, and ARA09C-St 12) that are found byproducts exhibit concave-up and/or kink type SO42- profiles. The physical properties and fluid pathways in sediment columns have been altered by these byproducts, which prevents the steady state condition of the dissolved species through them. Consequently, chemical zones are separated between bearing and non-bearing byproducts intervals under non-steady state condition from the seafloor to the sulfate-methane transition (SMT). GH dissociation also significantly impacts pore fluid properties (e.g., low Cl-, enriched δD and δ18O). The upward CH4 with depleted δ13C from the thermogenic origin affects the chemical signatures of MDACs. The enriched δ18O fluid from GH dissociation also influences the properties of MDACs. Thus, in the ARAON Mounds, the chemistry of the fluid and MDAC has significantly changed, most likely responding to the CH4 flux and GH dissociation through geological time. Overall, our findings will improve the understanding and prediction of the pore fluid and MDAC chemistry in the Arctic Ocean related to CH4 seepage by global climate change.

Tunnel cation and water structures of todorokite: Insights into metal partitioning and isotopic fractionation

Tectomanganate todorokite and phyllomanganate vernadite are the two major manganese minerals in marine ferromanganese sediments that contain large quantities of trace metals. Todorokite has a less clear metal partitioning mechanism than vernadite, mainly because the metal cation and water structures in the tunnel cavities remain poorly understood. Here, we report the composition-dependent tunnel-cation site disorder of todorokite obtained from molecular dynamics (MD) simulations. Our simulations of homocationic Ni2+-, Zn2+-, Mg2+-, Ca2+-, or Na+-todorokite revealed that tunnel cations form inner-sphere (IS) complexes with Mn octahedral surface at low hydration states, but at higher hydration states, outer-sphere (OS) complexes are the dominant cation species located at the center of the tunnel. However, K+ and Cs+ form only IS complexes regardless of the tunnel hydration state. Optimum water contents were determined based on the free energy changes associated with water intercalation into the tunnel cavities calculated as a function of water content for two heterocationic todorokite models: Mg0.5Na0.4Ca0.1Mn6O12·nH2O (Mg/Mn = 0.08, average Mn oxidation state = +3.73) and Mg1.1K0.1Ca0.1Mn6O12·nH2O (Mg/Mn = 0.18, average Mn oxidation state = +3.58). These models emulate the chemical compositions of well-characterized terrestrial and marine todorokite samples, respectively. At each optimum water content, MD simulations revealed that OS complexes are the major Mg2+ species in the former model. However, IS complexes are the major Mg2+ species in the latter model, indicating that the tunnel cation speciation of diagenetic todorokite can be influenced by the sediment pore-fluid chemistry. The atomic tunnel cation and water structures of todorokite provide a molecular basis for understanding of metal partitioning to Mn oxides and interpretation of metal stable isotopes recorded in ferromanganese nodules.

Influence of Pore Fluid Chemistry on Electrical Force-Dominated Fabrics of Fine-Grained Soils: Implications in Submerged Sediments

Structures to mitigate the climate change such as offshore wind farms and geological CO<sub>2</sub> sequestration would be located on coastal regions and offshores. Understanding of fine-grained soil fabrics in submerged conditions can help evaluate the safety of coastal underground constructions such as submarine excavation and slope stability. Fall cone tests for the liquid limit, grain-settling-based sedimentation tests, and ball penetration tests were conducted to investigate soil fabrics in different pore fluids with changes in ionic concentration and permittivity. Based on particle morphology and mineralogy, fine-grained soils were influenced by pore fluid chemistry. Fall cone tests showed the influence of pore fluid chemistry on uniformly mixed soil samples. Fine-grained soils that contained clay minerals such as kaolinite and bentonite showed significant liquid limit changes. Sedimentation tests and ball penetration tests induced fabrics with particle segregation and identified the type of fine-grained soils that could form gravitational force-dominated fabric or electrical force-dominated fabric during natural sedimentation process in submerged conditions.

Numerical Simulation of Cool Hydrothermal Processes in the Upper Volcanic Crust Beneath a Marine Sediment Pond: North Pond, North Atlantic Ocean

AbstractLow temperature hydrothermal systems hosted in the volcanic oceanic crust are responsible for ∼20% of Earth's global heat loss. Marine sediment ponds comprise an important type setting on young ridge flanks where hydrothermal circulation advectively extracts lithospheric heat, but the nature of coupled fluid‐heat transport in these settings remains poorly understood. Here we present coupled (fluid‐heat) numerical simulations of ocean crustal hydrogeology in and below North Pond, a sediment pond on ∼8 Ma seafloor of the North Atlantic Ocean. Two‐ and three‐dimensional simulations show that advective transport beneath North Pond is complex and time varying, with multiple spatial and temporal scales, consistent with seafloor and borehole observations. A unidirectional, single‐pass flow system is neither favored nor needed to match the spatial distribution of seafloor heat flux through North Pond sediments. When the permeability of the crustal aquifer is relatively high (10−10–10−9 m2), simulations can replicate much of the observed variability and suppression of seafloor heat flux and can explain basement overpressures and transient perturbations in pressure and temperature in the upper volcanic crust. Simulation results can also help explain heterogeneity in pore fluid chemistry and microbiology in the crust. Although driven by the same physical processes, the dynamics of hydrothermal circulation below North Pond are different from those seen on "discharge‐dominated" ridge flanks, where the permeability and exposed area of isolated basement outcrops control the extent of regional heat extraction.

Effect of Pore–Fluid Chemistry on the Undrained Shear Strength of Xanthan Gum Biopolymer-Treated Clays

Xanthan gum (XG) biopolymer-based soil treatment is an effective soil improvement method. In this study, we explored the effect of XG on the undrained shear strength of clays (kaolinite and montmorillonite) in chemically distinct pore fluids. Among the pore fluids tested, the undrained shear strength of kaolinite was the highest in kerosene, followed by deionized (DI) water and brine. This study hypothesized that the interparticle forces and interactions dominated the undrained shear strength of the kaolinite clay. In contrast, montmorillonite showed the highest undrained shear strength with DI water, followed by brine and kerosene, likely due to the increase in thickness of the viscous double layer that reduced the undrained strength of the montmorillonite clay. XG also affected the undrained shear strength of the clays, possibly due to the increase in viscosity of the pore fluids and modification of the clay interparticle fabrics. In DI water, XG increased the undrained shear strength of kaolinite (maximum shear strength was observed in the sample with an XG-to-soil mass ratio of 0.5%) via water absorption. Simultaneously, XG decreased the undrained shear strength of montmorillonite, likely due to XG-induced particle aggregation resulting from the changes in the montmorillonite particle surface charges. In 2-M-NaCl brine, the undrained shear strength increased with the increase in XG content, regardless of the mineral types, owing to the salt-induced double-layer compression and increase in concurrent XG-induced pore–fluid viscosity. However, the unaffected and constant undrained shear strength of both clays in nonpolar kerosene suggests that hydrating XG is a prerequisite for its application in soil treatment.

Impact of Particle Sizes, Mineralogy and Pore Fluid Chemistry on the Plasticity of Clayey Soils

The current classification of clayey soils does not entail information of pore fluid chemistry and particle size less than 75 µm. However, the pore fluid chemistry and particle size (at given mineralogy) are critical in the plasticity of clayey soils because of their impact on negative charge density. Therefore, this study extensively discusses the description of clay with respect to mineralogy, particle sizes, and pore fluid chemistry based on liquid and plastic limits of kaolinite, illite, and bentonite, and estimates undrained shear strength from the observed liquid limits. The liquid limits and undrained shear strength estimated from the observed liquid limits as a function of mineralogy (clay type), particle size, and ionic concentration reveal the need of incorporating pore fluid chemistry and particle size into the fines classification system. Furthermore, multiple linear regression models developed in this study demonstrate the importance of particle size and ionic concentration in predicting the liquid limit of clayey soils. This study also discusses the need for a comprehensive understanding of fines classification for proper interpretation of natural phenomena and engineering applications for fine-grained sediments.