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Several formulations of a nonlinear elastic behavior within the yield surface of the selected advanced constitutive models are described and compared. Since concentrating on geotechnical applications the accompanied numerical simulations are limited to basic laboratory tests such as isotropic compression, oedometer, and drained triaxial compression. The results show a significant influence of the size of the initial load step on final predictions particularly when starting from a very low initial stiffness associated with the assumed zero initial stress. Differences in the predicted response arising from different formulations are also discussed. These might be quite significant and the design engineer should be aware of that when choosing a particular computational software. [ABSTRACT FROM AUTHOR]

Constitutive models in the literature for creep of frozen soil are based on the direct use of time counted from the onset of creep. An explicit time dependence in a constitutive equation violates the principles of rational mechanics. No change in stress or temperature is allowed for during creep, using the time-based formulations. Moreover, the existing descriptions need much verification and improvement on the experimental side as well. Creep behaviour of artificially frozen sand was evaluated experimentally. Novel testing methods were used, and new insights into the creep behaviour of frozen soil were gained. Creep rate under uniaxial compression was examined with different kinds of interruptions, like unloadings or overloadings. Experimental creep curves were presented as functions of creep strain. They were brought to a dimensionless form which describes the creep universally, despite changes in stress or temperature. Possible anisotropy of frozen soil was revealed in the creep tests on cubic samples with changes of the loading direction. Using the particle image velocimetry (PIV) technique, information on the lateral deformation and the uniformity of creep were obtained. Volumetric creep of unsaturated frozen soil under isotropic compression was demonstrated to be due to the presence of air bubbles only. [ABSTRACT FROM AUTHOR]

Hydrate exploitation may trigger large-scale seafloor subsidence, especially when the depressurization method is used. The isotropic compression characteristics for methane hydrate-bearing soil (MHBS) need to be investigated to evaluate this deformation failure. Change in temperature and pore pressure (TP) condition can generate a considerable influence on the mechanical deformation and strength of MHBS. However, few studies focus on the isotropic compression deformation of MHBS. This paper carried out a series of isotropic compression tests on MHBS with different hydrate saturations and TP conditions. Experimental results show that the MHBS specimens exhibit a completely different isotropic compression curve at different hydrate saturations and TP conditions. The compressibility of MHBS is reduced remarkably with increased hydrate saturation, raised pore pressure, and decreased temperature. Hydrate saturation does not affect the compression index, but it explicitly reduces the swelling index. The yield stress is also enhanced with increasing hydrate saturation. The compression index of MHBS is independent of TP condition, while the swelling index is weakened and the yield stress is enhanced as temperature decreases and/or pore pressure increases. Through employing the phase state parameter as an indicator for TP condition, the influence of TP condition on the isotropic compression characteristics of MHBS is analyzed. Besides, the isotropic compression mechanism of MHBS at different hydrate saturation and TP condition is illustrated. • Temperature and pore pressure explicitly affect the isotropic compression behavior of MHBS. • Hydrate saturation and varying temperature and pore pressure apparently influence swelling index and yield stress. • Phase state parameter reasonably reflect the influence of temperature and pore pressure on isotropic compression. • Isotropic compression mechanism is revealed for MHBS. [ABSTRACT FROM AUTHOR]

Compacted loess is a special collapsible unsaturated soil and is sensitive to hydraulic conditions. Understanding and modeling the coupled hydromechanical behavior of compacted loess during isotropic compression is essential for establishing a complete constitutive model for unsaturated soils, which is of significance for predicting the deformation of loess fills in engineering. In this research, a series of constant suction isotropic compression tests are conducted to study the behavior of compacted loess. The experimental results show that volume change and soil–water characteristics are mutually affected during compression and that the normal compression curves flatten out and shift downward with the decrease in suction. Based on the experimental observations, the normal compression surface is modified, and the loading–collapse yield curve is deduced for the compacted loess. An equation associated with the void ratio is used to describe the effect of the volume change on the soil–water characteristics. Furthermore, a coupled hydromechanical constitutive model for the compacted loess under isotropic compression conditions is proposed within the framework of the Barcelona basic model. Model predictions of the mechanical and hydraulic behaviors of the compacted loess for constant suction isotropic compression tests and wetting tests at constant net stresses are compared with experimental data to verify the performance and validation of the proposed model. The comparisons indicate that the proposed model can accurately reproduce the coupled hydromechanical behavior of the compacted loess under isotropic compression conditions. [ABSTRACT FROM AUTHOR]

Salinity-induced soil degradation is a significant challenge in coastal reclamation areas, impacting agricultural productivity and infrastructure development. Variations in soil compression and deformation caused by changes in salinity warrant further investigation, particularly for agricultural applications. This study explores the relationship between soil pore water salinity and compressibility by conducting isotropic compression tests on salinized unsaturated agricultural soils treated with distilled water, 0.5 mol/L and 1 mol/L sodium chloride (NaCl) and calcium chloride (CaCl 2) solutions. The results demonstrate that the type and concentration of salts significantly affect the compression behavior of these soils. The constitutive parameters were calibrated based on the experimental data. To account for osmotic suction, Barcelona Basic Model (BBM) was adjusted. The findings indicate that as pore water salinity increases, soil compressibility decreases, reflected by a compression index (C c), and higher pre-consolidation stress (p y). This modification aimed to quantify the impact of pore water salinity on soil compression. To validate the constitutive model, a numerical analysis of an isotropic compression test was carried out. This study contributes to our understanding of the isotropic compression behavior of coastal saline soil, proposes a constitutive framework for predicting soil responses under different salt conditions, and provides theoretical support for engineering construction in coastal reclamation areas. • Isotropic compression test were performed on salinized unsaturated soils. • The compression index decreased with increasing pore water salinity. • Osmotic suction was considered in the Barcelona Basic Model (BBM). • The model can be well applied in simulating saline soil compression behavior. [ABSTRACT FROM AUTHOR]

It is now viable to use coarse-grained molecular dynamics (CGMD) to model interacting clay particles in simulations of soil mechanics element tests. In CGMD, particle interactions are described by the Gay-Berne (GB) potential, which can approximate the potential energy between clay particles as a function of their separation and relative orientations; however, a previous study identified a significant shortcoming of the GB potential, which is that it lacks a local maximum called the “energy barrier” that the true interaction possesses at very close range. In this study, we propose a modified GB potential which can capture the energy barrier at and we use this new potential function to simulate the clay mineral kaolinite under isotropic compression. Our simulations show that the energy barrier is a crucial ingredient required to reproduce the elastoplastic behaviour observed in laboratory tests upon unloading from an isotropic normally consolidated state. Our data show that the difference in mechanical behaviour between normally consolidated clay and overconsolidated clay can be explained by the fact that, during the initial loading, some pairs of interacting particles surmount the energy barrier so that they then experience a large attractive force. Effectively, these particles become bounded and do not separate when the stress applied to the sample is released. The response of overconsolidated clay to applied stress is stiffer than that of normally consolidated clay because a larger proportion of the clay particle interactions exist in this bonded state.

Suction piles are used to ensure wellhead stability during natural gas hydrate production in the Shenhu area of the South China Sea (SCS). Undrained shear properties of clayey-silty sediments play a critical role in the stability analysis of suction piles. However, it has not been fully studied. This study conducts a series of undrained triaxial shear tests on shallow clayey-silty sediments in the Shenhu area of SCS, and stress–strain curves under different overconsolidation ratio (OCR) conditions are obtained. OCR effects on undrained shear properties of clayey-silty sediments are discussed, and a model to predict the pore pressure coefficient at failure is proposed. Results show that the isotropic compression index is 0.175, and the isotropic swelling index is 0.029. The undrained shear strength is proportional to the effective confining pressure, and the proportionality coefficient is 0.42 for normally consolidated specimens, while the undrained shear strength of OC specimens nonlinearly increases with OCRs increasing. The proposed model aptly predicts the pore pressure coefficient at the failure of clayey-silty sediments of SCS with different OCRs. [ABSTRACT FROM AUTHOR]

The particle morphological properties, such as sphericity, concavity and convexity, of a granular assembly significantly affect its macroscopic and microscopic compressive behaviors under isotropic loading condition. However, limited studies on investigating the microscopic behavior of the granular assembly with real particle shapes under isotropic compression were reported. In this study, X-ray computed tomography (μCT) and discrete element modeling (DEM) were utilized to investigate isotropic compression behavior of the granular assembly with regard to the particle morphological properties, such as particle sphericity, concavity and interparticle frictions. The μCT was first used to extract the particle morphological parameters and then the DEM was utilized to numerically investigate the influences of the particle morphological properties on the isotropic compression behavior. The image reconstruction from μCT images indicated that the presented particle quantification algorithm was robust, and the presented microscopic analysis via the DEM simulation demonstrated that the particle surface concavity significantly affected the isotropic compression behavior. The observations of the particle connectivity and local void ratio distribution also provided insights into the granular assembly under isotropic compression. Results found that the particle concavity and interparticle friction influenced the most of the isotropic compression behavior of the granular assemblies.

The modified Cam-clay model has been widely adopted as the theoretical framework for constitutive modelling of clays. However, there is so far no such model for sands on the basis of which further development can be carried out. Based on the main differences in the behaviours exhibited during isotropic compression and shear processes between sands and clays, a basic constitutive model for sands is proposed by introducing the compressive hardening parameter p s and the critical state parameter χ into the formulations of normal compression line and elliptic yield surface of the modified Cam-clay model respectively. When the new compressive hardening parameter and critical state parameter both equal 0, the normal compression line and yield surface of the proposed model for sands can degrade into the corresponding ones of the modified Cam-clay model for clays. The comparison between test data and the model prediction indicates that the proposed model can predict the stress–strain relationship of normally compressed sands (i.e. the loosest sands without structure) well. The proposed model can be considered as the basic framework for further research on constitutive modelling of sands due to its clearly defined assumption, simple structure and good capability in model prediction. [ABSTRACT FROM AUTHOR]

The mechanical behaviors including strength and isotropic compression of granular soils under low confining pressure are systematically analyzed. The compressive hardening parameter ps is introduced in semi-logarithmic coordinates to express the curved normal compression line of granular soils in the e-ln p plane, to describe the little compressibility of granular soils under low confining pressure. The nonlinear variation of critical friction angle with confining pressure is considered by introducing the interlocking strength parameter τ0 into strength criteria. Based on the unified hardening model for clays and sands (CSUH model), the unified hardening (UH model) for granular soils considering low confining pressure, called UH-L model, is established. The UH-L model behaves significantly different with the CSUH model under low confining pressure, while tends to be same as the CSUH model with increasing confining pressure. The relationship between parameter ps and τ0cotφ, as well as the effect of ps and τ0cotφ on model performance are analyzed. Good agreement with the experimental data shows that the UH-L model is capable of uniformly describing the stress–strain relations and strength of granular soils with interparticle locking over a wide confining pressure load range, especially at low confining pressure. [ABSTRACT FROM AUTHOR]

Gypseous soil is one of the important high salt content soils in aired and semiarid areas. The failure problems of this soil occur due to the softening of soil and the dissolution of gypsum during leaching (if the flow is continuous). A significant lack of knowledge existed in this research area regarding the effects of leaching on the engineering properties and behavior of gypseous soil in both natural and treated conditions. In this paper, a series of consolidated drained triaxial permeability-leaching tests, under isotropic compression considering three confining pressures (i.e. 100, 200 and 300 kPa), has been carried out to study the effect of leaching on the geotechnical properties and behavior of gypseous soil. A high gypsum content sand soil with little fines was used in this study. Besides, dihydrate calcium chloride was used as an additive to improve the geotechnical properties of soil. The chemical additive percentages are 2.5% and 5.0% by weight of the dry soil. According to the test results, upon leaching, a large reduction in the cohesion of natural soil has been recorded, while the angle of internal friction approximately remained constant. Moreover, the natural soil became more compressible when subjected to leaching under isotropic condition. The inclusion of additive led to a reasonable reduction in permeability, leaching strain, and dissolution of gypsum, while, the shear strength parameters of treated soil were unaffected upon leaching. [ABSTRACT FROM AUTHOR]

Piezochromic luminescent materials that exhibit distinct luminescence responses to different types of mechanical stresses have been emerging as new kinds of materials which are rarely investigated. Herein, we report a donor–acceptor (D–A) charge‐transfer (CT) cocrystal, which shows distinct hypochromatic and bathochromatic shifts upon anisotropic grinding and isotropic compression, respectively. Detailed spectroscopic and structural analyses revealed that the hypochromatic shifted emission under grinding is attributable to a structural reorganization from a loosely segregated‐stack to a mixed‐stack, while the bathochromatic shifted emission originates from the formation of a tighter packing structure. We present rare evidence of a distinct luminescent response to anisotropic grinding and isotropic compression on the basis of structural rearrangement in a D–A cocrystal, and thus enriches our insight into piezochromic luminescence. Under pressure: Distinct luminescent responses to anisotropic grinding and isotropic compression are found for a donor–acceptor cocrystal, called CT‐R. It shows a unique enhanced hypochromatic shift emission under grinding, but a remarkable bathochromic‐shift emission under hydrostatic pressure. [ABSTRACT FROM AUTHOR]

To investigate the stress-dependent behavior of fly-ash blended cement (FAC)-admixed marine clay, isotropic consolidated drained (CID) triaxial tests were performed in the confining pressure range of 50-350 kPa. Stress dilatancy was observed when the confining pressure was in the lowest range of 50-100 kPa. The peak strength increased linearly with increasing confining pressure; this linear relationship was described by the following equation: pp = 1.7σ3 + 581 kPa, wherein pp is the peak strength and σ3 is the confining pressure. In the CID tests, failure modes of specimens were similar under different confining pressures. From the Mohr circles, it was found that the angle of shearing resistance was 52.8° and the cohesion intercept was 230.5 kPa. When the confining pressure was lower than the primary yield stress, some variation in the secant modulus were observed. However, the secant modulus tends to increase when the confining pressure exceeds the primary yield stress. [ABSTRACT FROM AUTHOR]

Cement-stabilized clay is widely used in soft clay improvement for deep excavation, underground construction, and land reclamation. This paper presents a study on the evaluation of elastic modulus for cement-stabilized marine clay. First, two types of cement-stabilized soils were studied through isotropic compression tests and cylinder split tensile tests. Specimens with different mix ratios and curing periods were used. Stress–strain behavior under isotropic compression was discussed, followed by an introduction and estimation of the stress-free bulk modulus. Empirical correlations between elastic moduli and functions for estimating elastic moduli were then proposed. Further estimation of elastic modulus was conducted with another data set. The results showed that the proposed function for estimating elastic modulus is effective for cement-improved marine clay. Finally, the proposed method and empirical functions were validated with other types of cement-stabilized clay. [ABSTRACT FROM PUBLISHER]

In material sciences, it is a well-known fact that linear or linearized theory based on Hooke's law does not offer a satisfactory description of solids in special regimes, which include e.g. too high strains under large uniaxial stresses. Therefore, in general, the response to biaxial or triaxial loading cannot be obtained as superposition of uniaxial load responses. Striking paper book example of material demonstrating such behavior is rubber subjected to uniaxial or isotropic compression. Despite this fact, linear mechanical moduli, being secant or differential, determined through standard rock-mechanics tests, mostly from the uniaxial compression, are still widely used for description of deformational behavior of rocks. Without doubt, an appropriate interpretation of these effective quasi-elastic or stiffness moduli can give useful information about mechanical properties of the rocks, especially in comparative sense. However, for more reliable constitutive modeling of any solid materials, paricularly rocks, an experimental investigation of deformational responses to uniaxial, biaxial and triaxial loading or unloading regimes is very useful. This contribution presents the results of an experimental case study on homogeneous sandstone exposed to isotropic triaxial, and equi-biaxial or uniaxial loading regimes. The measured deformational response of this rock is compared with behavior of elastic solid materials. Finally, benefit of the experimental testing for constitutive modeling based on phenomenological description is briefly discussed. [ABSTRACT FROM AUTHOR]

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Fibre-reinforced cemented sands have many applications in improving the response of soils. In this paper, an experimental investigation for the analysis of fiber-reinforced cemented sand in the framework of isotropic compression is presented. The experimental investigations were carried out using a high pressure triaxial apparatus having the capacity of 64 MPa of confining pressure. Tests have been conducted on Portaway sand specimens reinforced with randomly oriented discrete polypropylene fibers with different percentages of fiber and cement contents. Results are presented in the form of e-logp` curves as well as SEM (Scanning Electron Microscopy) micrographs. The effects of the addition of fibre in sand and cemented sand for different initial void ratios were investigated. The results demonstrate that the influence of fibre is not significant in both cemented and uncemented sand during the isotropic compression stage. Moreover, from the SEM micrographs it could be seen that there is breakage of sand particles and cement bonds. The fiber threads were seen pinched and found rarely broken in the specimen exhumed after isotropic compression.

We generate a large number of monodisperse disk packings in two dimensions via geometric-based packing algorithms including the relaxation algorithm and the Torquato–Jiao algorithm. Using the geometric-structure approach, a clear boundary of the geometrical feasible region in the order map is found which quite differs from that of the jammed region. For a certain packing density higher than 0.83, the crystalline degree varies in different packing samples. We find that the local hexatic order may increase in two fairly different ways as the system densifies. Therefore, two typical non-equilibrium jammed patterns, termed polycrystal and distorted crystal, are defined at high packing densities. Furthermore, their responses to isotropic compression are investigated using a compression–relaxation molecular dynamic protocol. The distorted crystal pattern is more stable than the polycrystal one with smaller displacements despite its low occurrence frequency. The results are helpful in understanding the structure and phase transition of disk packings. [ABSTRACT FROM AUTHOR]

We study the bulk properties of isotropic bidisperse granular mixtures using discrete element simulations. The focus is on the influence of the size (radius) ratio of the two constituents and volume fraction on the mixture properties. We show that the effective bulk modulus of a dense granular (base) assembly can be enhanced by up to 20% by substituting as little as 5% of its volume with smaller sized particles. Particles of similar sizes barely affect the macroscopic properties of the mixture. On the other extreme, when a huge number of fine particles are included, most of them lie in the voids of the base material, acting as rattlers, leading to an overall weakening effect. In between the limits, an optimum size ratio that maximizes the bulk modulus of the mixture is found. For loose systems, the bulk modulus decreases monotonically with addition of fines regardless of the size ratio. Finally, we relate the mixture properties to the ‘typical’ pore size in a disordered structure as induced by the combined effect of operating volume fraction (consolidation) and size ratio. [ABSTRACT FROM AUTHOR]

The crushing of sand particles under high stress leads to decrease the shear resistance of the soil. Previously, some theoretical procedures were presented for the quantitative investigation of crushing in sand during shear loading, based on the work equilibrium. However, these equations cannot be applied to crushing in sand under pure isotropic compression due to the absence of a frictional term in the work equation. This paper proposes a theoretical procedure for volumetric strain and consequent work equilibrium in an element subjected to isotropic compression. In this procedure, participant of the rearrangement and crushing in sample volumetric strain is separated, and then, the corresponding work of each contribution is determined. Moreover, isotropic compression tests are conducted on two sands from Hormuz Island and Bushehr Port in the Persian Gulf. The test results showed that the compressibility of both sands increased as density decreased. In addition, the study found that Bushehr sand was more susceptible to compressibility and crushing than Hormuz sand. Moreover, the validity of the new theoretical equation of energy equilibrium was verified by applying it to the experimental data. According to the verification results, the theoretical equation is properly conformed to the experimental data and the analogous parameters were close, with an error of up to 30%. In addition, surface energy parameter in isotropic compression was obtained at a higher magnitude relative to shear loading, which implied that the loading type affected the crushing of sand grains. [ABSTRACT FROM AUTHOR]

A series of isotropic and triaxial compression tests was conducted on artificial methane hydrate-bearing fine-grained sediment (HBFS) specimens prepared via the excess-gas method. It is shown that the swelling index decreases and the yield stress increases linearly with the increase of the hydrate saturation, whereas the compression index is practically independent of hydrate saturation. The HBFS generally exhibits strain-hardening behavior, though strain-softening behavior may occur at low confining net stress and high hydrate saturation. The presence of hydrate can increase the stiffness and shear strength of the HBFS to various degrees, depending upon the applied confining net stress. It is revealed that the effect of hydrate cementation on the shear strength is weakened under high confining net stress conditions, owing to the deterioration of hydrate cementation. The hydrate cementation can influence the shear dilatancy of the HBFS, an effect that becomes less pronounced as the applied confining net stress increases. Based on the experimental results, empirical formulations are developed for the yield stress, strength, and shear dilatancy of the HBFS. The experimental results provide a comprehensive dataset for validating the constitutive models of HBFS. • Tested methane hydrate-bearing fine-grained sediment (HBFS) in isotropic and triaxial compression. • HBFS yield stress exhibited a linear increase with increasing hydrate saturation. • Proposed an HBFS strength equation based on hydrate cementation deterioration. • Analyzed HBFS dilatancy in terms of net confining stress and hydrate saturation. • Proposed an empirical expression to characterize HBFS dilatancy behavior. [ABSTRACT FROM AUTHOR]

• The stress-solid materials-voids interaction was researched in detail. • A piecewise function was proposed to describe the variation of air-voids with stress. • The isotropic yield strength and structure failure strength in isotropic compression were defined and analyzed. Solid materials and voids were two significant components for foamed concretes and had the characteristic of coordinated deformation. However, two parts seemed disconnected to date. This research investigated the stress-solid materials-voids interaction by conducting isotropic compression experiments. The stress–strain curves, deformation process, ν -ln p curves, and key mechanical parameters were analyzed in detail. The results indicated that the stress–strain curves in isotropic compression could be divided into three phases: initial elastic stage, voids compression stage, and densification stage. The ν -ln p curves were deduced to describe the reduction in porosity along with the stress. Correspondingly, the isotropic yield strength and structure failure strength were proposed to characterize the strength variation of solid materials in isotropic compression. Based on two strengths, the features of solid materials with elastic deformation and compressing pores were illustrated in detail. Furthermore, a piecewise function was proposed to describe the ν -ln p relationship, and corresponding compression indexes were established to calculate the rate of voids compression. Besides, the isotropic yield strength was related to the mix condition and was on average 25.2% larger than the uniaxial compressive strength. Moreover, the final volume strain was a little smaller than the initial void ratio, signifying that foamed concretes possessed some micro-pores that could not be filled by solid materials. [ABSTRACT FROM AUTHOR]

Soil stabilization refers to the process of changing soil properties to improve strength and durability and the load carrying capacity of the soil. The analysis of reinforced soil for complete understanding of its mechanical behavior requires the preparation of the representative composite specimens. However, obtaining a homogenous and consistent composite specimen is a tedious task. In this paper, the sample preparation of artificially cemented and geosynthetic reinforced cemented soils with controlled initial relative density, void ratio and varying percent of fiber and cement content is described, and example results are presented for a range of soils. 100 mm height and 50 mm diameter samples were prepared for high pressure triaxial testing to determine the mechanical behaviour of artificially cemented and fiber reinforced cemented sands. Several difficulties in the preparation and testing of samples were identified and discussed. [ABSTRACT FROM AUTHOR]