Saturated Clay Research Articles

Application of a modified mixed hardening model to cyclic degradation of saturated clay

Application of a modified mixed hardening model to cyclic degradation of saturated clay

Thermo-elasto-plastic constitutive model of saturated clay considering state-dependent

Thermo-elasto-plastic constitutive model of saturated clay considering state-dependent

Analytical study on included angle of double-plate vertically loaded anchors in saturated clay

The double-plate vertically loaded anchor (DPVLA) represents a new type of anchor. To maximize the ultimate pullout capacity of a DPVLA in saturated clay, it is crucial to determine the included angle corresponding to the maximum pullout capacity (IAMPC). An expression for the IAMPC of the DPVLA in saturated clay has been derived based on its mechanical model. Furthermore, the influence of various parameters on the IAMPC is analyzed based on the derived expression. The effect of the IAMPC of the DPVLA on the critical embedment depth has been investigated through finite element analysis. The results indicate that, aside from the area of the auxiliary fluke, the IAMPC of the DPVLA is significantly influenced by other parameters, which also impact the ultimate pullout capacity associated with IAMPC, except for the adhesion factor. Additionally, it is also found that the critical embedment depth of a DPVLA, with the main fluke area equal to that of the auxiliary fluke, increases with the IAMPC until a -maximum critical embedment depth is reached. These findings provide valuable insights for the design and installation of DPVLAs in saturated clay environments.

Quantitative investigation of temperature-dependent bound water degeneration in bentonite clays

Temperature increases in saturated clay alter the physicochemical clay-water interactions and may lead to the conversion of bound water into free water. These changes significantly influence the physical, chemical, and engineering properties of clays, which are critical for geotechnical and geological engineering and minimizing risks in areas with expansive clay soils. However, quantifying this phenomenon remains challenging in the literature. This study presents a robust experimental approach for quantifying the thermal-induced conversion of bound water in clays, providing valuable insights into the mechanisms governing their thermo-mechanical behavior. A novel experimental method is proposed to quantify the degenerated bound water content in a clay system subjected to temperatures ranging from 20 to 50 °C. The research employs the siphon principle to examine volume changes in a clay system at elevated temperatures, focusing on measuring the conversion of bound water to free water. This method accounts for thermal expansion of both the soil constituents and the confining glass cylinder, as well as potential evaporation losses. To validate the setup's accuracy, a calibration test using standard Ottawa sand with negligible bound water was performed. After measuring system error, the primary outcome was calibrated. Results showed that at 30 °C, 40 °C, and 50 °C, 3 %, 9 %, and 15 % of the initial bound water, respectively, converted to free water.

Specific ion effects on the soil shear strength and clay surface properties of collapsing wall in Benggang.

Benggangs are a special type of soil erosion in the hilly granite regions of the tropical and subtropical areas of Southern China. They cause severe soil and water loss, which can severely deteriorate soil quality and threat to the local ecological environment. Soils (red soil, sandy soil and detritus soil) were collected from collapsing wall of a typical Benggang in Changting County of Fujian Province, and their physicochemical and mineralogical properties were analyzed. Five different monovalent cations were used to saturate the soil samples to examine the specific ion effects on the shear strength and clay surface properties. Red soil had a higher clay content, plastic limit, liquid limit and shear strength than sandy soil and detritus soil. The studied soils mainly consisted of kaolinite, hydroxy-interlayer vermiculite, illite and gibbsite clay minerals. The soils saturated with K+, NH4 +and Cs+ had greater cohesion than the Li+- and Na+-saturated soils, e.g., the cohesion of the red soil saturated with Li+, K+, NH4 + and Cs+ cations were 1.05, 1.23, 1.45 and 1.20 times larger than that of the Na+-saturated soil, respectively. While the internal friction angle was slightly different, which indicated that different monovalent cations affected the shear strength differently. K+-, NH4 +- and Cs+-saturated clay particles had higher zeta potentials and thinner shear plane thicknesses than Li+- and Na+-saturated clay particles and showed strong specific ion effects on the clay surface properties. The changes in clay surface properties strongly affected the soil mechanical properties. Soils saturated with K+, NH4 + and Cs+ could increase the shear strength, and then increase the stability of the collapsing wall, thus might decrease the erosion intensity of Benggang. The results provide a scientific basis for the interpretation of and practical treatment of Benggang.

Insight into nonlinear thermal consolidation of saturated clay under coupled thermo-mechanical loading: a unified one-dimensional model

Insight into nonlinear thermal consolidation of saturated clay under coupled thermo-mechanical loading: a unified one-dimensional model

Influence of drainage conditions on piezocone penetration mechanism in offshore clays

ABSTRACT CPTu (piezocone penetration test) is widely used in engineering practice to determine various parameters of clays under partially drained conditions. However, most existing research is based on undrained or fully drained conditions for clays, leading to underestimation or overestimation of soil strength. By applying the Eulerian-Lagrangian large deformation finite element method to analyse the water-soil interaction, the CPTu driving mechanism in offshore saturated soft clays under different drainage conditions is revealed. An advanced hypoplastic constitutive model for clays is used to simulate the nonlinear behaviour of kaolin under different drainage conditions. The generation, accumulation, and dissipation of excess pore water pressure under different drainage conditions are analysed, as well as the influence of excess pore water pressure on cone tip resistance and the effective stress of the soil during the CPTu penetration process.

Experimental investigation of the roughness, freezing temperature and normal stress on the shear mechanical action of frozen saturated clay-rock interface

Recently, with the increase in global temperature, the permafrost degradation trend has intensified, and the soil-rock binary slope in permafrost regions has become more unstable. Therefore, this paper focuses on the shear strength of the clay-rock interface in the binary slope. The three-dimensional roughness, freezing temperature, and normal stress are key factors affecting the shear strength of the clay-rock interface. The influence of freezing temperature can be further quantified by using the unfrozen water content (UWC), which was measured by nuclear magnetic resonance (NMR) technology. By analyzing experimental results, it can be concluded that the three-dimensional roughness can effectively improve the shear strength of the clay-rock interface under freezing conditions, and the shear strength increases with the growth of the climbing angle (ic). The influence of temperature can be attributed to the effect of UWC on the internal friction angle and cohesion of saturated clay. Compared with the internal friction angle, the cohesion of saturated clay decreases faster with the increase of UWC. In addition, the shear strength of the clay-rock interface rises linearly as the normal stress increases, therefore the Mohr-Coulomb criterion also can be used to characterize the shear strength of the clay-rock interface. An interesting finding is that significant tensile cracks will appear in the clay part around the large bulge under low normal stress and high roughness. It further confirmed the contribution of large bulges to the prevention of shear slides of soft clay. The quantification understanding of the shear mechanical action of the clay-rock interface can provide a reference for scientific disaster reduction in cold regions.

Coupled model for electro‐osmosis consolidation and ion transport considering chemical osmosis in saturated clay soils

AbstractThe electro‐osmosis approach efficiently facilitates the rapid dewatering of soil with high water content and contributes to reducing contaminant levels within the clay soil. However, the changes of chemical field caused by ion transport in the clay soil during electro‐osmosis process will also influence the clay soil consolidation effect. Existing theories predominantly tend to disregard this crucial physical process and its resultant effects, thereby restraining a comprehensive analysis of electro‐osmosis consolidation (EOC) behavior under intricate chemical conditions. This study introduces a concise model of EOC and ion transport considering chemical osmosis. The model considers the nonlinear variation of clay soil parameters such as compressibility, permeability, and effective diffusion coefficients, along with the interaction between EOC and ion transport. Meanwhile, the correctness of the model is verified from different aspects such as theoretical derivation and model comparison. Based on the proposed model, the impacts of the variation in electrical field intensity and chemical concentration on the coupled behaviors between EOC and ion transport are systematically investigated, with and without incorporating nonlinear consolidation characteristics. The results show that diffusion and electro‐migration exhibit a more pronounced effect on ion transport during EOC. Simultaneously, with the increase of ion concentration in clay soil pore solution, the effects of chemical osmosis become increasingly apparent, thereby enhancing clay soil settlement.

A unified thermo-mechanical bounding surface model for saturated clay and sand

To accurately predict soil thermal effects is of great importance for simulations of complex boundary value problems such as the energy foundations and nuclear waste disposal. Existing thermo-mechanical constitutive models only account for clay, and cannot simulate the sand’s behaviour under thermo-mechanical conditions. In this study, a unified thermo-mechanical bounding surface (UTMBS) model is proposed for saturated clay and sand. Based on the thermal effects on the isotropic compression line, the model proposes a new unified thermal softening relationship and a plastic modulus for clay and sand, with the thermal cyclic behaviour replicated by a memory surface. The unified model considers the thermal effects on the critical state line and the shape of the bounding surface, accounting for both drained and undrained shearing of clay and sand at different temperatures. In addition, the non-linear elasticity relationship represents the hysteresis loops of the stress–strain relationship in the mechanical cycles. The performance of the proposed model is evaluated against existing experimental results for clay and sand in terms of their thermal cyclic behaviour, drained/undrained triaxial compression, and mechanical cyclic behaviour at different temperatures. It is evident that the UTMBS model is able to simulate various thermo-mechanical behaviours of clay and sand.

Undrained behavior of marine clay under one-way cyclic loading with variable confining pressure

Settlement of roads or railway caused by traffic loading has a serious effect on the safety and service performance of transport infrastructures constructed on soft marine clay. While simple cyclic triaxial test with constant confining pressure (CCP) were used in most of the previous studies, a series of cyclic triaxial tests with variable confining pressure (VCP) were carried out on normally consolidated (NC) and overconsolidated (OC) reconstituted Wenzhou soft clay in this paper to study the undrained behavior of soft marine clay due to surcharge preloading as well as cyclic traffic loading. VCP test is able to approximate the complicated stress path than CCP test caused by traffic loading. The test results indicate that NC specimens show significantly different pore water pressure (u) evolution compared with OC specimens. However, a change in the overconsolidation ratio (OCR) of OC specimens does not have a significant influence on variation of u with identical cyclic stress ratio (CSR) and total stress path (η). The slope of the effective stress path is dependent on the total stress path under which the specimen was loaded cyclically, regardless of the OCR and whether variable confining pressure was applied. The slope of the effective stress path is broadly in line with the slope of corresponding total stress path. In addition, the development of permanent axial strain (εpa) due to one-way cyclic loading was shown to depend significantly on the values of η and OCR. Both the variable confining pressure and OCR limited the strain accumulation of saturated marine clay under undrained one-way cyclic loading. Finally, the effects of η and OCR on the magnitude of εpa after 1000 loading cycles are quantified and incorporated in a power law function for the permanent deformation prediction of soft marine clay due to traffic loading.

Analisis Perubahan Volume pada Timbunan Tanah Lempung Berdasarkan Nilai Batas Susut (SNI 3422:2008)

Sedimentation has continuously resulted in siltation of the port of Pelabuhan Perikanan Samudera (PPS) Lampulo located in Kuta Alam District, Banda Aceh City. The dredged soil collected outside the port area visually indicates clay soil. In addition to the low bearing capacity and high plasticity, the effect of water on clay is high swelling and shrinkage. One of the prominent behaviors that cause major damage to structures built on clay is associated with volume decrease i.e., shrinkage in saturated compressible clay soil when water get evaporated. Shrinkage in clay will result in volume changes. The purpose of this research is to calculate the volume changes in mound of clay soil based on shrinkage limit values using SNI 3422:2008. The soil sample used is an undisturbed sample (UDS) originating from the dredging area of the port of PPS Lampulo. The test consists of water content, specific gravity, liquid limit, plastic limit, shrinkage limit and grain size distribution using the SNI method. Based on the results of the index properties test, according to AASHTO the soil sample belongs to group A-7-5 which means it is a clay soil with a GI value greater than 20, so it is considered poor as a subgrade soil. According to USCS, the soil belongs to the CH classification, which means clay soil with high plasticity, so it has a large potential for expansion and shrinkage. Based on SNI 3422:2008, the average shrinkage limit (SL) is 21.21%, the average shrinkage ratio (R) is 2.27% and the average linear shrinkage (LS) is 9.65%. With an average volume change (VC) value of 35.59%, the shrinkage volume of soil embankment of the dredging area of the port of PPS Lampulo is 32,438.85 m3 compared to its initial volume (91,145.97 m3). Therefore, the shrinkage limit is an important parameter for calculating the volume shrinkage in mound of soil due to the soil type is clay with high plasticity.

Consolidation and seepage solutions in enclosure space based on non-zero-constant values boundary.

Research is ongoing to find solutions to the problem of Consolidation and seepage in saturated clay in enclosure space. Firstly, the boundary of non-zero-constant values is established, considering the seepage boundary of the clay is affected by pumping water or lowering boundary pressure on the site. Secondly, the differential equation is established to reflect the spatial and temporal variations of excess pore water pressure dissipation in the clay in enclosure space, and the solution is derived using variable separation methods. Finally, based on results of the solution derived, contour maps of the water pressure are drawn corresponding with the different inhomogeneous boundary conditions.

Three-Dimensional Upper Bound Solution to Estimate Soil Thrust of a Track System on Saturated Clay Slopes under Undrained Conditions

This study proposes a three-dimensional upper bound solution for estimating the soil thrust of tracked vehicles on saturated clay slopes. The present study considered block, triangular wedge, and trapezoidal wedge failure modes to formulate an upper bound solution for each. The analytical solution for soil thrust was determined as the minimum upper bound solution among those for each failure mode. This analytical solution was validated through numerical simulations that modeled track-ground interactions. Parametric studies, based on the upper bound solution, assessed the impact of track system shape, vehicle weight, undrained shear strength, and ground slope on soil thrust. The analytical solutions and parametric studies provide a rapid method for assessing vehicle operability on clay slopes and offer references for designing tracked vehicles suitable for site conditions.

Creep Characteristics of Reconstituted Silty Clay under Different Pre-Loading Path Histories

Due to the long-term deformation settlement of foundations, issues such as damage and functional failure of buildings and structures have long been a concern in the engineering field. The creep of soil is one of the primary causes leading to long-term deformation of foundations. In this paper, the consolidation deformation, creep characteristics, and creep model of reconstituted saturated silty clay were studied using the isotropic consolidation creep test and triaxial compression creep test. The results show that for the isotropic consolidation creep test, although the applied load adopted different stages of loading, as long as the final applied confining pressure was the same, the number of stages applied by the confining pressure had little effect on the final isotropic consolidation deformation of the sample and the triaxial undrained shear strength after creep. However, for the triaxial shear creep test, it was found that under the same final deviatoric stress, the final deviatoric strain of the sample was closely related to the number of loading stages of deviatoric stress. The test showed that the more loading stages with the same deviatoric stress, the smaller the final deviatoric strain, and the triaxial undrained shear strength of the sample after creep increased. In addition, it was reasonable to set the pore pressure dissipation of the sample at 95% ((u0 − u)/u0 = 95%) as the time (t100) at which the primary consolidation of the soil sample was completed. The isotropic consolidation creep curves and the triaxial compression creep curves showed certain non-linearity. Then, the logarithmic model and the hyperbolic model were used to fit the creep curves of the samples. It was found that the hyperbolic model had a better fitting effect than the logarithmic model, but for the triaxial compression creep test, the creep parameters of the sample changed greatly. Therefore, studying the creep characteristics of soil under different pre-loading steps is of significant engineering importance for evaluating the long-term deformation of underground structures.

A semi‐analytical model for coupled THM consolidation of saturated clays improved by PVTD considering thermal contraction

AbstractPrevious studies have demonstrated that saturated normally consolidated and lightly over‐consolidated clays undergo contraction when heated due to a reduction in preconsolidation pressure. A linear constitutive model is proposed to describe the thermal contraction, with this model, governing equations are developed for the coupled thermo‐hydro‐mechanical (THM) consolidation induced by a prefabricated vertical thermo‐drain (PVTD). Corresponding semi‐analytical solutions are derived employing the Laplace transform and validated via comparison with experimental results, existing numerical model, and custom finite element method (FEM) model. Subsequently, comprehensive parametric analyses are carried out to investigate the THM coupling consolidation behaviors of the clays. Outcomes show that aside from surcharge load, generation of excess pore water pressure in soils can also be induced by thermal contraction, difference in thermal expansibility between pore water and soil grains, and thermo‐osmosis, where the influence of thermal contraction on the excess pore water pressure is the most prominent among the three factors.

Analysis of hole wall stability in saturated clay using undrained solution for cylindrical cavity contraction

To investigate the stress state of soil during the instability of the hole wall (hole shrinkage) in saturated clay, the theory of cylindrical cavity contraction in an infinite medium is applied, utilizing the modified Cam-Clay (MCC) model. By employing intermediate variables, the issue of cylindrical cavity contraction is reformulated into a first-order ordinary differential equation in Lagrangian form, with three effective stress components and pore pressure as the unknowns. In MATLAB, the stress conditions at the elastoplastic boundary serve as the initial values for solving the initial value problem of the differential equation system. After determining the correlation between the stress distribution around the cavity and the diameter reduction ratio, the analysis proceeds to evaluate the internal support pressure required for stabilizing the hole wall according to various stability criteria. This pressure is then integrated into the hole wall stability coefficient formula within the soil pressure model, facilitating the evaluation of hole wall stability. The effectiveness and accuracy of the proposed semi-analytical elastic–plastic solutions were subsequently confirmed through comparison with finite element analysis results, underscoring its relevance for addressing hole wall stability challenges.

A thermoplastic clay constitutive model with temperature dependent evolution of stress anisotropy

This paper presents a thermomechanical constitutive model that captures temperature dependent evolutions of preconsolidation stress and stress anisotropy in normally consolidated and lightly overconsolidated saturated clays. Following a non-associative flow rule, the model was formulated to account for the rate of evolution of stress anisotropy as a function of temperature. A temperature-dependent rotational hardening parameter was introduced and calibrated employing a simple optimization algorithm for four different clays. The developed model was further implemented in a finite element (FE) analysis software for use in boundary value problems. Success of such numerical implementation and predictive performance of the constitutive model was further verified through FE simulations of drained and undrained triaxial tests on saturated clays at reference and elevated temperature. FEA results obtained from these simulations agreed very well with test data reported in the literature.

A new method for rapid preparing high-strength saturated clay samples in large-scale model tests

The preparation of high-strength saturated clay samples for large-scale model tests presents a significant challenge in geotechnical engineering. The slurry consolidation method has been conventionally employed to prepare saturated clay, despite its time-consuming and labor-intensive nature. Therefore, this study proposes a rapid preparation technique for clayey soils utilizing the dynamic compaction method, enabling the facile preparation of saturated clay samples by compacting the soils from an unsaturated state. During compaction, the void ratio decreases, thereby increasing the degree of saturation and enhancing the soil strength. Critical to this method are two variables: the moisture water content and the soil density, which are determined through bench-scale compaction tests using the Proctor compaction test apparatus. These tests establish the relationships between moisture content and density, degree of saturation, and soil strength. The moisture content aligning with the target soil strength is selected as the target moisture content for model-scale soil preparation, whereas the moisture content-density relationship sets the target density value. The laboratory tests validate that the soil strength of the saturated model-size clay samples prepared using the proposed method fulfills the requisite criteria, indicating its effectiveness for rapid preparation of high-strength saturated clay samples in large-scale model tests.

Calculation model of depth under quantification of surface morphology of dry shrinkage cracks in red clay

Cracks commonly form in clay owing to water loss, negatively affecting strength and hydraulic properties of soil, leading to rock and soil damage including landslides and dam instability. Understanding the changing patterns of the shrinkage crack depth is crucial for exploring slope infiltration patterns and determining key factors for slope stability. This study suggests a relationship between the surface and depth variations during cracking, and investigates the influence of the surface roughness on shrinkage cracks in saturated red clay. Regression analysis and machine learning algorithms were used to establish a depth prediction model. (1) Based on the surface morphology of shrinkage cracks, they are categorized into three types: linear, curved, and inflectional (linear and curved are the main types). (2) The surface roughness and development rate of surface cracks were positively correlated. (3) Based on the geometric parameters of the crack surface, a prediction model (error within 15%) for crack depth was established using multivariate nonlinear regression, providing a reference for the initial assessment of crack depth. These results provide a better understanding of the development patterns of shrinkage cracks, whose influence on slope stability is critical for mitigating the risks associated with slope instability and other soil failures.