Behavior Of Clay Research Articles

Sustainable Stabilization of Brown and Green Clays Using Industrial By-products

Background The disposal of industrial by-products and the rising cost of construction materials are critical issues globally, particularly in developing nations such as Jordan. Brown and green clay are considered problematic types of soft clay, as they fail to meet the necessary specifications for use in construction. Objective This study aims to assess the efficiency of Cement Kiln Dust (CKD) and Silica Fume (S.F.) as stabilizing agents for brown and green clays. The research explores how CKD and S.F. can be used as cost-efficient and eco-friendly alternatives to enhance the mechanical properties of soft clays, improving their viability for construction. Methods An experimental approach was used to investigate the impact of CKD and S.F. on brown and green clay stabilization. The study examines the effect of varying CKD and S.F. concentrations on the clays' plasticity, compaction, unconfined compressive strength, and consolidation properties. CKD was tested at four different levels (0%, 5%, 10%, and 15%), as was S.F. (0%, 5%, 10%, and 15%). Results The findings revealed a notable enhancement in the engineering properties and behavior of both brown and green clay, with reductions observed in the plasticity index (P.I.), compression index (Cc), compressive strength (qc), and maximum dry density (γd). Conclusion Adding 15% CKD to brown clay resulted in the most significant improvements after a curing period of 7 days based on the unconfined compressive strength test results.

Effective Stress-Based Numerical Method for Predicting Large-Diameter Monopile Response to Various Lateral Cyclic Loadings

Extreme marine environmental cyclic loading significantly affects the serviceability of monopiles applied for the foundation of offshore wind turbines (OWTs). Existing research has primarily used p-y methods or total stress-based models to investigate the behavior of monopile–marine clay systems, overlooking the pore pressure development in subsea clay. Studies on the effective stress-based behavior of clay under various lateral cyclic loading conditions are limited. This paper presents an effective stress-based 3D finite element numerical method developed to predict key behaviors of pile–clay systems, including permanent pile rotation under cyclic loading, pile bending moment, and the evolution of pore pressure in subsea clay. The model is verified by contrasting the simulations results to centrifuge experimental results. Cyclic lateral loading is divided into average cyclic load and amplitude of cyclic load to investigate their impacts on the pile–clay system response. The research findings offer insights for the design of large-diameter monopiles under complex cyclic loading conditions.

Investigating temperature effects on the shear behavior of clays: Molecular dynamics simulations

The shear behavior of clays is critically important for the stability and safety of nuclear waste repositories and clay gouges. These contexts expose clayey geomaterials to high pressures and temperatures. Under such varying conditions, the shear behavior of these materials becomes complex, necessitating thorough investigations. This study aims to elucidate the effect of temperature on the shear behavior of three clayey materials: kaolinite, illite, and montmorillonite—through Molecular Dynamics. The research replicates a geotechnical shear setup at the molecular scale, varying the temperature (including sub-freezing temperatures below 300 K and elevated temperatures 400-500 K and hydrostatic pressures. The results reveal stick-slip behavior, enabling the calculation of nanoscale cohesion, friction angle, and shear modulus across different temperatures. Thermal effects are notably significant for illite and kaolinite, both exhibiting a marked decrease in shear properties with increasing temperature. Kaolinite demonstrates a high shear modulus of up to 40 GPa, indicating substantial shear strength. Illite displays the highest friction angle among the studied materials. For montmorillonite, thermal effects on shear behaviour is comparatively less pronounced. This study provides critical insights into the mechanical behaviour of clays under varying thermal conditions, contributing to the broader understanding of geomaterial stability in high-stake environments.

Generalized Effective Stress of Dual-Porosity Geomaterials Considering Thermochemical Effects

The accurate calculating of effective stress is crucial to predicting soil deformation and ensuring structural safety under complex mechanical, thermal, and chemical loads. In this study, the thermodynamic pressures of the solid phase, and liquid phases in macropores and micropores of dual-porosity geomaterials are determined on the basis of thermodynamics and conservation equations with considering for the impact of temperature and solute concentration on soil-water interactions. In particular, thermal pressurization related to temperature, and generalized osmotic pressure related to solute concentration were incorporated into the liquid-phase thermodynamic pressure equations. Thereafter, an equation for the generalized effective stress that could be applied specifically to dual-porosity geotechnical materials with consideration for environmental loads was derived from the definition of the stress tensor. The deformation behavior of clay under mechanical, thermal, and chemical coupling loading conditions was predicted using the newly proposed generalized effective stress. Predicted results revealed a stronger correlation between the generalized effective stress and void ratio, thereby confirming the accuracy and effectiveness of the proposed approach. The derived equation establishes a solid theoretical foundation for designing impermeable buffer barriers in geotechnical engineering and geo-environmental engineering safety assessments.

Atomistic origin of montmorillonite clay subjected to freeze-thaw hysteresis

The freeze-thaw cycles of frozen soil could significantly affect its thermo-hydro-mechanical-chemical (THMC) properties, causing the frost heaving and thawing settlement. The microscale essence is the water-ice phase transition, but the microscale details are still poorly understood, especially at ultra-low temperatures. Nuclear magnetic resonance (NMR) technology and molecular dynamics (MD) simulation methods were performed to explore the freeze-thaw behaviors of montmorillonite clay under temperature of 210 - 293 K. Then, the water-ice phase transition, freeze-thaw hysteresis, ice nucleation mechanism, and surface effect of clay at an atomistic level were discussed. A classification method of different types of unfrozen water through NMR experiment was proposed, including bulk, capillary, and bound water. Here, it is found that: (1) the freeze-thaw process of frozen soil at the macroscale was essentially the occurrence of ice-water phase transition at the microscale. (2) The freeze-thaw hysteresis was caused by different growth and melting rates of ice crystals, where the ice growth/nucleation on clay surface was more difficult to develop. (3) The surface effect of clay was essential for the ice nucleation and the existence of bound water. For example, little unfrozen water still existed in unfrozen soil even at 213 K. (4) For unsaturated frozen soil, the quasi-liquid water was an essential component of unfrozen water that cannot be ignored. This work could provide an atomistic insight to unravel the atomistic origin of the freeze-thaw mechanism of montmorillonite clay and complement relevant experimental evidence.

Synergetic Effects of Alkaline and Sulfate-Based Waste Binders on Undrained Triaxial Behavior of Cement-Admixed Soft Clay

Synergetic Effects of Alkaline and Sulfate-Based Waste Binders on Undrained Triaxial Behavior of Cement-Admixed Soft Clay

Investigation of cracking behavior of fine-grained clays exposed to different humidity environments and engineering implications based on X-ray computed tomography

Due to the humidity difference between fine-grained clay and atmosphere environment, the complex crack network is formed, which is the main channel for water storage and migration and hence poses a potential threat to engineering construction. Therefore, the appropriate characterization of cracking behavior of fine-grained clay is of great significance for exploring its microphysical properties. To this end, this work took expansive soils as research object and a series of desiccation tests and X-ray computed tomography tests were conducted to investigate the shrinkage cracking behavior. The results indicate that a higher desiccation rate records a smaller shrinkage strain, but it aggravates the cracking on a much larger scale. Especially at high desiccation rates, two-dimensional crack ratio shows a significant fluctuation. Small cracks tend to turn into large ones during desiccation, and the increasing desiccation rate primarily exerts a significant effect on the cracks with equivalent radius more than 1000 µm. The expansive soil is dominated by horizontal cracks, and a low desiccation rate mainly promotes the connection between horizontal cracks, whereas high desiccation rates enhance the connectivity of oblique cracks, which exerts an adverse effect on soil slopes. Besides, the rise in desiccation rate leads to a wealth of micro-scale pores and throats occurring in the soil. The fine-grained clays at higher desiccation rates present larger pore and throat volume, more connected pores, and higher average coordination number, thus enhancing the connectivity between pore and pore. Permeability simulation results also confirm the positive correlation between connected crack ratio and hydraulic conductivity of the soil. In terms of engineering significance, narrowing down the difference in humidity between fine-grained clays and atmosphere is the most effective measure to constrain the extension of cracks.

A systematic investigation of the freezing process of silty clay through unidirectional stepwise freezing method combined with digital imaging processing technology

Soil freezing represents a complex thermo-hydro-mechanical coupling process that encompasses a range of physical and mechanical phenomena, such as heat transfer, moisture migration, cryostructure development, ice lens segregation, frost heave, and consolidation, all of which interact and influence one another throughout the freezing process. This study conducted a unidirectional stepwise freezing test, comprising three distinct freezing stages, to investigate the freezing behavior of Qinghai-Tibet silty clay using digital imaging processing technology (DIPT), which includes an image acquisition system and a digital image processing system. The results demonstrate that the stepwise freezing test provides a more comprehensive insight into the physical and mechanical processes occurring during unidirectional soil freezing. At various stages of freezing, the temperature distribution within the sample achieves a linear stabilization, with the frozen zone exhibiting a slightly larger extent compared to the unfrozen zone. The longitudinal section of the sample developed layered cryogenic cracks, whereas the horizontal section revealed interconnected cryogenic polygonal cracks of varying sizes, which facilitated moisture migration and ice segregation. Furthermore, ice lenses can segregate within a broad temperature range below the soil freezing point in the frozen zone, resulting in frost heave within the frozen zone and consolidation of the unfrozen zone. This study proposes an experimental method to clarify the complex phenomenon and mechanisms of frost heave during soil freezing.

Study of the one-dimensional consolidation and creep of clays with different thicknesses using different hypotheses and three elastic visco-plastic models

The one-dimensional consolidation analysis of clays considering creep compression is a classical issue in soil mechanics and geotechnical design. The major debate lies in how to predict the consolidation settlement for a thick layer in the field using parameters obtained from a thin specimen from the laboratory. Different hypotheses have been advocated, based on which various methods and constitutive models have been developed. However, there are still some questions unaddressed and concepts inconsistently used, which may mislead engineers in the selection of methods/models and may result in settlements underestimated on a risk design side. In this paper, a state-of-the-art review and a thorough comparison study are performed on the existing methods and models for the consolidation analysis of clays exhibiting creep, from theoretical derivations to numerical simulations in comparison with soil test data. An in-depth discussion is carried out on several key issues related to the thickness effects on the time-dependent compression behaviour of clays. The arguments of Hypothesis A and Hypothesis B are revisited based on the current development of constitutive theories. Three existing elastic visco-plastic (EVP) models that consider the creep compression implicitly during the whole consolidation process can perform well in predicting the settlement of clay layers with different thicknesses, and are in line with Hypothesis B. It is concluded that using existing EVP models based on porous-media continuum mechanics is a rigorous scientific method (also called “rigorous” Hypothesis B method), which is superior to the old Hypothesis A method which has logic errors and may result in unsafe underestimation of settlements.

Investigation of strain-softening behaviours and development of constitutive model of red clays in Guiyang, China

Red clay is widely used in engineering projects; it is characterized by high moisture content, high plasticity, large porosity, high strength and low compressibility. The engineering properties and deformation modelling of red clay in Guiyang differ significantly from those of ordinary soils. Consequently, it is essential to conduct a detailed study of the stress–strain relationship of red clay in order to obtain accurate engineering parameters. Hence, a series of unconsolidated undrained triaxial compression tests (UU) was conducted on red clay in Guiyang under different water contents and confining pressures. The test results show that the stress–strain curve of the clay undergoes three stages: elastic deformation, plastic yielding and stress reduction after failure. After reaching peak deviatoric stress, the deviatoric stress decreases gradually and stabilizes, showing noticeable strain-softening characteristics. The non-linear model from the Nanjing Hydraulic Research Institute (NHRI) was introduced for fitting and obtaining relevant parameters. Then, based on the FLAC 3D platform, numerical simulation was carried out on a standard soil sample. The research results show that the calculated curve from the non-linear model fits the experimental curve quite well, and the numerical test curve also agrees with it. This indicates that the non-linear model from NHRI can effectively reflect the strain-softening behaviour of clay and is highly applicable to Guiyang red clay.

Comparative Analysis of Foundation Systems in Expansive Soil: A Three-Dimensional Model Approach to Moisture Diffusion and Volume Changes

This study compares the performance of various foundation systems in expansive soils, such as mats, granular anchor piles, and concrete piles. Expansive soils experience volumetric changes due to moisture fluctuations, which can lead to structural damage. Abaqus software, in conjunction with the SCV approach, is used to analyze soil-foundation interactions. A custom subroutine enhances simulation accuracy by incorporating empirical data on unsaturated clay behavior, matric suction, and variations in effective stress. The method’s accuracy is validated by comparing simulation results to field and laboratory experiments. The findings indicate that increasing the applied load on mats decreases overall heave but increases the differential heave. Additionally, higher soil permeability dereases the differential heave of mats. Granular anchor piles outperform concrete piles by more than 50% in highly expansive soils, suggesting a preference for these foundations. This study provides insights into the behavior of expansive soils, which will assist engineers in designing resilient foundation systems for structures.

Effects of reconsolidation on cyclic deformation behaviours of a kaolin clay

Effects of reconsolidation on cyclic deformation behaviours of a kaolin clay

A simplified strategy to simulate the nonlinear behavior of clay for seismic SSI analysis

A simplified strategy to simulate the nonlinear behavior of clay for seismic SSI analysis

Enhanced understanding on permanent deformation behaviour of subgrade compacted clay under long-term cyclic loading

The long-term performance of pavement structures is heavily reliant on the sustained load-carrying capacity of the subgrade soil. Under repetitive traffic loads, permanent deformation (PD) gradually accumulates in the subgrade due to plastic yielding and soil particle rearrangement, which can compromise the serviceability and durability of overlying pavement layers. This study aimed to enhance the understanding of compacted clay response under long-term cyclic loads through a systematic repeated load triaxial (RLT) testing approach. The proposed approach considered depth-dependent static and dynamic stresses exerted on compacted clay beneath pavement structures and traffic loads. A series of RLT tests were conducted to investigate the impact of key factors, including soil properties (moisture content and compaction degree), stress conditions (confining pressure and deviator stress), and load characteristics (load duration and rest period), on the PD behaviour of compacted clay subgrade. Stress-strain hysteresis loops and damping ratios were analyzed to enhance the fundamental understanding of subgrade PD evolution. The results showed that higher moisture content and lower compaction degree significantly increased PD, with the PD response transitioning from plastic shakedown to plastic creep. Greater deviator stress also exacerbated PD accumulation. Variations in loading duration and rest period influenced the PD behaviour, demonstrating the importance of accurately simulating the stress history experienced by subgrade soil elements under traffic loading. The findings provide valuable insights to optimize subgrade design and implement performance-based management of pavements.

Dynamic behavior of kaolin clay under bidirectional cyclic loading for suction bucket foundation

The stability of offshore wind turbine (OWT) foundations is largely influenced by the dynamic characteristics of marine clay. In offshore engineering, marine clays may exposed to bidirectional cyclic stresses. To empirically examine the influence of different cyclic stress magnitudes on the dynamic characteristics of marine clay at different depth, a sequence of dynamic triaxial tests is conducted on marine kaolin clay, encompassing diverse values of the cyclic stress ratio (CSR) and effective confining pressure (p'0). Some valuable inferences have been drawn: At low cyclic stress ratios (CSR≤0.3), the axial strain (εa), stiffness (k), and excess pore water pressure (EPWP) of the specimen exhibit logarithmic increase, logarithmic decrease, and logarithmic accumulation, respectively. Under high cyclic stress ratio conditions (CSR＞0.3), the axial strain increases linearly, the stiffness deteriorates linearly, and the logarithmic excess pore water pressure accumulates. After analyzing the dynamic characteristics data of kaolin clay, the correlation between excess pore water pressure and axial strain was established. By analyzing the vertical cyclic mechanism of suction bucket foundation, a prediction model for suction bucket foundation under vertical cyclic loading was established based on the dynamic characteristics of marine clay and the model was validated. The comparison between the validation outcomes and the experimental outcomes shows good agreement. This study provides certain guidance for the design of suction bucket foundations for OWTs.

Micro to macro investigation of clays advising their constitutive modelling - part II

This paper reports the second part of the keynote lecture, whose part I has been already published in this journal, presenting extensive experimental research on the investigation of clay microstructure and its evolution upon loading. Whether the first part focused on the micro to macro behaviour of different reconstituted clays, this part instead concerns the microscale features of the corresponding natural clays, their changes under different loading paths and the ensuing constitutive modelling implications. The experimental investigation is carried out according to the methodology outlined in the part I-paper, hence micro-scale analyses are presented on natural clays subjected to macro-scale mechanical testing, with the purpose to provide experimental evidence of the processes at the micro-scale which underlie the clay response at the macroscale. As for the reconstituted clays in the part I-paper, original results on stiff Pappadai and Lucera clay, this time in their natural state, are compared to literature results on clays of different classes, either soft or stiff. The results presented in this paper, together with those discussed in the part I, allow for a conceptual modelling of the microstructure evolution under compression of natural versus reconstituted multi-mineral clays, providing microstructural insights into the macro-behaviour described by constitutive laws and advising their mathematical formalization in the framework of either continuum mechanics or micro-mechanics.

Fully coupled finite strain consolidation analysis for soft clay treated by prefabricated horizontal drain with vacuum and heat preloading

This paper established a one-dimensional fully coupled finite strain consolidation analysis for soft clay treated by thermal prefabricated horizontal drain under vacuum and heat preloading with the consideration of thermal elastic viscoplastic (TEVP) behaviors of soft clay. Firstly, the governing equations for finite strain consolidation, heat conduction, and heat convention process have been carefully derived based on the well-established Gibson’s large strain consolidation theory and TEVP constitutive model. Secondly, the accuracy and reliability of the numerical method have been verified with benchmark cases and three physical model tests. Then, improvement of consolidation efficiency rate (IER) was defined and used to study the effect of three variables on consolidation efficiency. Last but not least, a graphical user interface (GUI) was provided to support researchers and engineers in utilizing the proposed numerical method for conducting consolidation analysis of soft soil treated in the same or similar fashion.

Disintegration behaviors of red clay under wet-dry cycles

Cyclic wetting-drying alternation has a significant influence on the strength and structure of soils. It is prone to causing soil softening and disintegration, highlighting the importance to improve the soil's resistance to disintegration. This paper utilizes a self-developed disintegration test apparatus to analyze the disintegration characteristics of improved red soil under wet-dry cycles, focusing on the disintegration amount and ratio. Furthermore, XRD (X-ray diffraction), SEM (scanning electron microscope), tensile test, and contact angle test are employed to investigate the anti-disintegration behaviors of the improved red soil. The results show that the disintegrating amount and ratio of undisturbed and improved red soil are distinctly different under wet-dry cycles. Linear, stepped, constant and concave but perfect "S" shapes of the disintegrating ratio are observed in the cyclic tests. Cement and lime strengthen the red soil primarily through hydration reaction. The drop experiment confirms that cement plays a crucial role in restraining the disintegration. When the ameliorant content is low, the correlation between pore parameters and disintegration duration of red soil follows the order: mean shape coefficient > fractal dimension > probability entropy > area probability distribution index. With a high ameliorant content, the correlation remains similar, with slightly higher correlation for probability entropy. Under wet-dry cycle conditions, sludge and kaolin can improve the soil through the bonding of clay particles. The improved water repellency greatly enhances the resistance to disintegration of the altered red soil. The research provides valuable insights for the practical application of soil.

Effect of Freeze–Thaw–Dry–Wet Cycles on the Shear Behavior of Silty Clay Salinized in Wetting Processes

Effect of Freeze–Thaw–Dry–Wet Cycles on the Shear Behavior of Silty Clay Salinized in Wetting Processes

Behaviour of wet clay due to off-road traffic loading

Abstract The presence of water in the soil can greatly affect the trafficability of off-roading vehicles, making it difficult to operate. As the water content increases, it can eventually lead to sinkage and immobility. Despite the relevance of this topic in many applications, such as military, agricultural, and earthmoving vehicles, the studies available on tire and moist soil interaction are limited. The numerical modeling of such a system is very challenging because it requires accounting for hydro-mechanical effects, large deformations, non-linear behavior, and complex interactions between the tire and the soil. This work contributes to the understanding of the behavior of moist clay under the influence of traffic loading. In particular, the preliminary results of numeric simulations to study the interaction between moist clay and a passing tire using physics-based techniques are presented. A great emphasis is given to the development of an accurate soil model that can capture the fundamental characteristics of moist clays in saturated conditions.