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The response of a structure–foundation system subjected to loading is a function of the interaction between them. If the response is to be analyzed accurately, the effect of roughness at the interface needs to be considered. This study is an investigation of the interface behavior of concrete (rock-like) specimens with four different surface roughnesses, experimentally and numerically. To provide roughness at the interface, an innovative three-dimensional (3D) printing technology was used to create roughness on the surface of concrete specimens. A series of uniaxial compression, interface normal compression, monotonic, and one-way cyclic shear tests was performed. The disturbed state concept (DSC) constitutive model was used to define the interface behavior under shear deformation by simulating both prepeak and postpeak behaviors, including microstructural modifications and softening in deforming materials. The results of the interface tests were used to determine the parameters of the DSC model. These parameters were obtained as dependent on both surface roughness Rs and joint roughness coefficient (JRC) at the interface. DSC parameters, such as normal and shear stiffnesses, and ultimate, phase change, hardening, and disturbance parameters, were derived as functions of Rs and JRC. The friction angle variation with JRC was also determined and validated with a high accuracy. The foregoing are some of the novel aspects in this study. The resulting parameters were used to validate the DSC model by back-predicting both the tests that were used for determining the parameters and the independent tests that were not used for parameter determination. Satisfactory correlation was observed between computational predictions and test measurements. [ABSTRACT FROM AUTHOR]

Zheng et al. ([56]) utilized X-ray computed tomography to obtain evolutions of particle breakage and particle shape of crushable sands through a series of one-dimensional compression tests. The addition of water weakened microhardness and strength of particles, resulting in an increase in particle breakage and particle surface corrugation. The special collection on Testing and Modeling on Particle Breakage for Granular Soils is available in the ASCE Library (https://ascelibrary.org/ijgnai/testing modeling granular soils). [Extracted from the article]

This paper presents a simplified solution for consolidation of plastic clays under cyclic loading in disturbed state concept (DSC) framework. When normally consolidated (NC) clay undergoes cyclic loading, at the beginning of the loading, it is in a normally consolidated state. In each cycle of loading until the average ratio of consolidation is less than its maximum value in the last cycle of loading, the clay is in an overconsolidated (OC) state and then becomes normally consolidated. The process continues until a certain number of cycles have occurred and the clay reaches the OC state during all the loading cycles, which is called the steady-state condition. There is a gradual and continuous change from NC to OC state in successive loading half-cycles. The changing properties of the clay during cyclic loading mean that it is impossible to find a closed-form solution for this problem. Because the state of the clay changes gradually from a known NC state at the beginning to a known OC state at the final steady state, DSC can be adapted to this kind of problem using propitious state functions describing the changes in clay state. An analytical solution of a consolidation partial differential equation is used to obtain a general state function. The state function is used to describe the gradual change in state of the clay from OC to NC during successive cycles. Then the solutions of the problem in two elastic conditions of NC and OC states are interpolated using a derived state function to obtain the solution of the plastic problem. The validity of this method is ensured by a series of numerical and experimental tests. [ABSTRACT FROM AUTHOR]

Computer methods have opened a new era for accurate and economic analysis and design of engineering problems. They account for many significant factors such as arbitrary geometries, nonhomogeneities in material composition, complex boundary conditions, nonlinear material behavior (constitutive modeling) and complex loading conditions, which were difficult to include in conventional and closed form solution procedures. Constitutive modeling characterizes the mechanical behavior of solids and contacts (e.g. interfaces and joints), and plays perhaps the most important role for realistic solutions from procedures in computational mechanics. A great number of constitutive models, from simple to the advanced, have been proposed. Most of them account for specific characteristics of the material. However, a deforming material may experience, simultaneously, many characteristics such as elastic, plastic and creep strains, different loading (stress) paths, volume change under shear stress, microcracking leading to fracture and failure, strain softening or degradation, and healing or strengthening. Hence, there is a need for developing unified models that account for these characteristics. The main objective of these two papers is to present a brief review of the available constitutive models, and identify their capabilities and limitations; then a novel and unified approach, called the disturbed state concept (DSC) with hierarchical single surface (HISS) plasticity, is presented including its theoretical background, constitutive parameters and their determination, and validation at the test specimen and boundary value problem levels. The general capabilities of the DSC/HISS approach are emphasized by its application for a wide range of materials and contacts (interfaces and joints). Because of its generality, the DSC contains many previous models as special cases. The presentation is divided in two papers. This paper (Part 1) contains the review of various models, and then description of the DSC/HISS model and its analysis for issues such as mesh dependence and localization. Part 1 also contains the capability of the DSC/HISS model to define the behavior of both solids and contacts. Validations of the DSC/HISS model at the specimen and boundary value problem levels for a wide range of materials and contacts are included in the compendium paper, Part 2. The idea of the DSC is considered to be relatively simple, and it can be easily implemented in computer procedures. It is believed that the DSC can provide a realistic and unified approach for constitutive modeling for a wide range of materials and contacts. [ABSTRACT FROM AUTHOR]

Computer methods have opened a new era for accurate and economic analysis and design of engineering problems. They account for many significant factors such as arbitrary geometries, nonhomogeneities in material composition, complex boundary conditions, nonlinear material behavior (constitutive modeling) and complex loading conditions, which were difficult to include in conventional and closed form solution procedures. Constitutive modeling characterizes the mechanical behavior of solids and contacts (e.g. interfaces and joints), and plays perhaps the most important role for realistic solutions from procedures in computational mechanics. A great number of constitutive models, from the simple to the advanced, have been proposed. Most of them account for specific characteristics of the material. However, a deforming material may experience simultaneously, many characteristics such as elastic, plastic and creep strains, different loading (stress) paths, volume change under shear stress, microcracking leading to fracture and failure, strain softening or degradation, and healing or strengthening. Hence, there is a need for developing unified models that accounts for these characteristics. The main objective of these papers is to present a review of the available constitutive models, and identify their capabilities and limitations; then a novel and unified approach, called the disturbed state concept (DSC) with the hierarchical single surface (HISS) plasticity, is presented including its theoretical background, constitutive parameters and their determination, and validation at the test specimen and boundary value problem levels. The general capabilities of the DSC/HISS approach are emphasized by its application for a wide range of materials and contacts (interfaces and joints). Because of its generality, the DSC contains many previous models as special cases. The presentation is divided in two papers. The review of various models and then description of the DSC/HISS model and its analysis for issues such as mesh dependence and localization have been presented in Part 1, which also contains the capability of the DSC/HISS model to define both solids and contacts. Validations of the DSC/HISS model at the specimen and boundary value problem levels for a wide range of materials and contacts are included in this Part 2. The DSC is considered to be relatively simple, and it can be easily implemented in computer procedures. It is believed that the DSC can provide a realistic and unified approach for constitutive modeling for a wide range of materials and contacts. [ABSTRACT FROM AUTHOR]

Abstract: A nonlinear finite element method with eight-noded isoparametric quadrilateral elements for concrete and two-noded elements for reinforcement was used to predict the behavior of reinforced concrete frame structures. The disturbed state concept (DSC) and the hierarchical single surface (HISS) plasticity model with the associated modified flow rule were used to characterize the constitutive behavior of concrete in both compression and tension. The DSC model allows for the characterization of non-associative behavior through the use of disturbance, and it computes microcracking during deformation, which eventually leads to fracture and failure. In the DSC model, the critical disturbance, D c , identifies fracture and failure. Elastic perfectly plastic behavior is assumed in models of steel reinforcement. The DSC model was validated at two levels: (1) specimen and (2) practical boundary value problem. At the specimen level, predictions are obtained by integrating the incremental constitutive relations. The finite element procedure and the DSC model are used to obtain predictions for practical boundary value problems. Based on comparisons between DSC predictions and test data, the model is capable of providing highly satisfactory predictions. [Copyright &y& Elsevier]

The disturbed state concept (DSC) is used to characterize the deformation behavior of glacial tills, which may have a significant role in the motion of overlying glaciers with attendant implications for global climate dynamics. The model includes elastic, plastic, and creep deformation; microstructural modifications leading to softening and failure; and effect of rate of loading. This paper also presents a procedure to construct the static yield surface, which is essential to model the full creep response of the material. Laboratory triaxial tests are performed to calibrate the model. Predictions are compared with the test data, which include independent validations. A finite-element (FE) program with the implementation of the DSC model is used to predict the motion of an idealized ice sheet as affected by the deformation in the till. A novel concept is proposed to predict the failure and resulting motion of ice sheets. The concept involves the definition of state in the deforming till when stress, strain, and the disturbance reach critical values beyond the peak stress. The proposed concept is considered to be more realistic than the commonly used Mohr-Coulomb (M-C) criterion, in which failure and motion are assumed to occur at the peak stress with very small (elastic) strains. [ABSTRACT FROM AUTHOR]

Need for unified and mechanistic constitutive models for pavement materials for evaluation of various distresses has been recognized; however, such models are not yet available. There have been efforts to develop unified models; however, they have been based usually on ad hoc combinations of models for special properties such as elastic, plastic, creep and fracture, often without appropriate connections to various coupled responses of bound and unbound materials, they may result and in a large number of parameters, often without physical meanings. The disturbed state concept (DSC) provides a modeling approach that includes various responses such as elastic, plastic, creep, microcracking and fracture, softening and healing under mechanical and environmental (thermal, moisture, etc.) within a single unified and coupled framework. A brief review is presented to identify the advantages of the DSC compared to other available models. The DSC has been validated and applied to a wide range of materials: geologic, asphalt, concrete, ceramic, metal alloys, and silicon. It allows for evaluation of various distresses such as permanent deformations (rutting), microcracking and fracture, reflection cracking, thermal cracking, and healing. The DSC is implemented in two- and three-dimensional finite-element (FE) procedures, which allow static, repetitive, and dynamic loads including elastic, plastic, creep, microcracking leading to fracture and failure. A number of examples are solved for various distresses considering flexible (asphalt) pavements; however, the DSC model is applicable to rigid (concrete) pavements also. It is felt that the DSC and the FE computer programs provide unique and novel approaches for pavement engineering. It is desirable to perform further research and applications including validation with respect to simulated and field behavior of pavements. [ABSTRACT FROM AUTHOR]

In this study, an analytical model is developed to establish a framework for predicting the coefficient of lateral soil pressure in unsaturated soils. To this end, the disturbed state concept (DSC) is implemented along with the concept of effective stress for unsaturated soils. Accordingly, upper and lower limits are considered for the structural disturbance of the soil during hydromechanical loading, and a suction-dependent analytical framework is proposed for calculating continuous variations of the coefficient of lateral soil pressure, from the at-rest to active state of the soil, against the effective vertical stress parameter. The functionality of the proposed model is verified against experimental results obtained from a series of laboratory unsaturated drained tests conducted on two different soil materials (a Sand–Kaolin mixture and Firouzkouh Clay) with two initial void ratios. Quantitative comparisons show excellent conformance between the predicted and experimental data. A practical example of calculating lateral soil pressure on a gravity retaining wall is also presented, in which the results obtained from the model presented in this study and the conventional classic approach of calculating the lateral soil pressure on retaining walls are compared. It is hoped that the results of this study can help researchers and designers to obtain improved values of lateral soil pressure in unsaturated soil. [ABSTRACT FROM AUTHOR]

The disturbed state concept (DSC)-based model for overconsolidated clay was proposed mainly in a previous paper that aims to analyze the influences of the model parameters on model predictions, calibrations of the model parameters, and the model validation through different overconsolidated clays. It is found that the disturbance parameter in the model predictions can greatly influence the evolution of stress, volumetric strain, undrained shear strength, and excess pore pressure with axial strain. Detailed calibrations of the model parameters, such as the disturbance parameter, potential-failure and dilatancy parameters, and plastic modulus parameters, are introduced. The comparison results demonstrate that the DSC-based model predictions are in good agreement with the test data of different overconsolidated clays on strain softening and volumetric expansion under the drained condition, as well as the evolution of undrained shear strength and excess pore pressure during the undrained shearing process. [ABSTRACT FROM AUTHOR]

The disturbed state concept (DSC) is widely used to capture the cracking, breaking, heating, softening, and hardening behaviors of geomaterials. In this study, a constitutive model for overconsolidated clays is proposed by incorporating the DSC. A new disturbance function describes the effect of the overconsolidation ratio (OCR) on the strength, dilatancy, and deformation of overconsolidated clays. This disturbance function is incorporated into the potential-failure and dilatancy stress ratios, potential-failure and dilatancy lines, and potential-failure and dilatancy surfaces at the current and referenced states. The plastic moduli also pertain to this disturbance function. With the assistance of this disturbance function, the proposed model can capture the strain hardening and volumetric contraction of normally consolidated or slightly overconsolidated clays, as well as the strain softening and volumetric expansion of highly overconsolidated clays under the drained condition. It can also capture the evolution of strength, excess pore pressure, and stress paths under the undrained condition. [ABSTRACT FROM AUTHOR]

Biotreatment is an emerging reinforcement technology. Avalanche dynamics has recently been used to analyze the fracture behavior of biotreated specimens under unconfined conditions. However, the avalanche dynamics along with fractures in biotreated specimens under confined conditions have not yet been investigated. In this study, we aimed to determine the basic laws of the avalanche dynamics for biotreated calcareous sand specimens through a series of triaxial compression tests under various confining pressures. We found that the probability density distributions of acoustic emission signal (AES) energy, the AES amplitude, and the AES duration of the biotreated specimens under confined conditions obeyed the damped power law, and the AES waiting-time distribution followed the prediction by the gamma function. However, the confining pressure had no significant influence on the relative magnitude, the aftershock-sequence distribution, the AES energy-versus-amplitude distribution, or the AES amplitude-versus-duration distribution. More importantly, the maximum-likelihood estimation of the AES energy could be used to predict the occurrence of catastrophic damage in the biotreated soils. [ABSTRACT FROM AUTHOR]

Wetting deformation of the rockfill material, which is generated by particle sliding, breakage, and rearrangement, plays a vital role in earth-rockfill dam deformation that determines the safety of the dam. However, the previous wetting deformation particle breakage test was performed under the conventional stress path, which could not reflect the influence of stress path. This paper investigates the particle breakage of the basalt rockfill used in the Gushui dam during wetting deformation tests under the equal stress ratio path and drained triaxial shearing tests under the complex stress path. The results indicate that stress path, stress level, stress intensity, and particle breakage determine the wetting deformation under the equal stress ratio path. Under a low confining pressure (1,000 kPa), rockfill particle sliding and roll over are loosely constrained, and negligible particle breakage occurs during wetting deformation, which is mostly generated by particle sliding and rearrangement. Under a high confining pressure (2,000 kPa), rockfill particle sliding and roll over are more constrained. Thus, the contact force significantly increases and significant particle breakage occurs during wetting deformation. In addition, the relationship between the relative particle breakage index and plastic work under the equal stress ratio path and the following wetting deformation period can be simulated with a hyperbolic formulation, which cannot reasonably simulate the particle breakage under the transitional stress path after wetting deformation. The wetting deformation function under the equal stress ratio path was developed to incorporate the influence of the particle breakage and stress path. [ABSTRACT FROM AUTHOR]

Time-dependent deformation of crushable soils attributable to particle breakage could dominate the postconstruction stability of high rockfill dams and pile foundations. The evolutionary trends of the volumetric strain, particle-size distribution (PSD), and particle breakage of carbonate sands with 10% fines content for various loading durations and vertical stress levels are investigated by performing a series of one-dimensional compression tests. Loading durations ranging from 1 to 10,000 min, vertical stress levels ranging from 200 to 3,200 kPa, and fines content percentages ranging from 0 to 20 are considered. The results indicate that the increased loading duration in the initial stage has a significant effect on the volumetric strain; however, as the loading duration increases, this effect gradually decreases. In addition, the PSD curve shifts upward as the loading duration increases, indicating that the amount of particle breakage increases accordingly. Both the loading duration and the vertical stress can induce PSD changes in carbonate sands. Empirical equations are proposed to describe the relationship between the relative particle breakage index and the loading duration as well as the relationship between the relative particle breakage index and the vertical stress. [ABSTRACT FROM AUTHOR]

Assessing the hydromechanical behavior of collapsible soils is always a challenging topic in an unsaturated soil mechanics context. Although numerous efforts have been made thus far to establish frameworks for explaining the stress-strain behavior of collapsible soils, many of them are developed based on the results from conventional tests without controlling or measuring the unsaturated state variables. Furthermore, modeling the hydromechanical behavior of chemical-stabilized collapsible soils has been rarely studied. To establish a constitutive model for predicting the behavior of a lime-stabilized collapsible soil, the results obtained from filter paper and unsaturated odometer tests on a lime-treated loessial soil (which are presented in a companion paper) have been analyzed by considering the effective stress approach for unsaturated soils. An empirical model for explaining the load-collapse behavior of lime-stabilized tested soil is presented. Moreover, by implementing the disturbed state concept (DSC) method, a coupled semiempirical hydromechanical model is developed to predict the disturbance level and calculate the soil strain due to application of the vertical stress in Ko condition. Both presented models in this research are introduced as functions of two important governing state and material variables, namely matric suction and lime content. Results show excellent conformance between the laboratory test results and model predictions. [ABSTRACT FROM AUTHOR]

An abstract of the article "General Stress-Dilatancy Relation for Granular," by Yang Xiao and colleagues is presented.

The true triaxial compression test is the three-dimensional test, where the intermediate principal stress is not less than the minor principal stress and not more than the major principal stress. The effect of the intermediate principal stress ratio (i.e., the b-value) on particle breakage of rockfill material (RFM) was investigated by conducting a series of true triaxial compression tests under the constant-p' and constant-b loading condition. It was observed that the relative breakage extent of RFM increased with an increase in confining pressure but decreased with an increase in b-value. The effect of the b-value on the particle breakage of RFM was well predicted by an empirical equation. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study on the evolution of particle shape in carbonate sands that underwent different degrees of particle breakage. Carbonate sand specimens with three different initial particle sizes were subjected to impact loadings with different input energies. The particle sizes and shapes of the tested sands were analyzed by dynamic image analysis both before and after each loading. An increase in the input energy resulted in increases in particle breakage, aspect ratio, sphericity, and roundness to steady-state values, whereas convexity was barely influenced in the tests. It was found that the Weibull distribution could be used to describe the cumulative distributions of the particle-shape parameters. A relative shape-variation index for quantitatively describing the change in particle shape was correlated with the relative breakage index, which quantitatively describes the extent of particle breakage. Based on microscopic images of the particles at different loading states, the dominant particle-breakage mode gradually transited from the initial fracture mode to the attrition and abrasion mode with an increase in input energy, leading to the production of much more rounded and spherical particles. [ABSTRACT FROM AUTHOR]

Degradation of geomaterials, that is, particle breakage, can be harmful to the full life-cycle stability of practical engineering; for example, rockfill dam, energy-pile foundation, railway embankment, and retaining wall. A key issue is how to precisely quantify grain crushing during the life-cycle operation of the project that suffers high pressure or dynamic loading. This paper reviews the advantages and limitations of existing particle breakage indices and proposes a new simple breakage index for estimating the evolution of grain crushing. The new index without an integral grading area can be easily and directly obtained from the sieving results and independent of the coordinate of particle size axis. It can also adequately capture the grain crushing at all grain sizes. Moreover, it can be used for uniformly graded, well-graded, and gap-graded crushable soils. [ABSTRACT FROM AUTHOR]

Aeolian loess deposits are among problematic collapsible soils whose substantial settlements due to the increase in moisture content, stress level, or a combination of both, frequently cause serious structural failures, financial losses, and casualties worldwide. One way to increase the strength and bearing capacity of collapsible soils is to chemically stabilize them with lime. The behavior of lime-stabilized collapsible soils has been investigated mainly by conducting conventional laboratory tests without any measurement or control of unsaturated state variables, such as matric suction. In this research, the hydromechanical behavior of a reconstituted lime-stabilized loessial soil is investigated by conducting unsaturated suction-controlled odometer tests. For this purpose, variable vertical loads have been imposed on the unsaturated lime-stabilized loessial soil specimens (with different amounts of lime content) under constant matric suctions. During all unsaturated odometer tests, unsaturated state variables (e.g., matric suction, degree of saturation, volume change of the tested specimens) have been simultaneously controlled and measured. To capture the hydraulic characteristics of the soil, along with odometer tests, soil-water retention curves (SWRCs) of specimens have been obtained for both wetting and drying paths by conducting filter paper tests. Furthermore, to investigate the effects of adding lime to the evolution of soil pore structures, scanning electron microscope (SEM) micrographs have been captured from the structure of the soil specimens. Results of laboratory tests showed that adding a small amount of lime to collapsible loessial soils not only reduces the collapse-induced volume changes to a large extent, but also can increase the yield strength of the soil. Moreover, it was revealed that further increase of lime content in loessial soil specimens beyond a specific value has no significant influence on the hydromechanical characteristics of the treated soil. In a companion paper, the results from unsaturated odometer tests on treated and untreated loessial soil reported in this paper have been analyzed in an unsaturated effective stress context, and an empirical model for explaining the load-collapse behavior of the soil is presented. Also by implementing the disturbed state concept (DSC), a coupled semiempirical hydromechanical model is developed to predict the disturbance level and calculate the soil strains under applying vertical stress in the Ko condition. [ABSTRACT FROM AUTHOR]

An abstract of the article "New Method for Improvement of Rockfill Material with Polyurethane Foam Adhesive" by Yang Xiao, Hanong Liu and Chandrakant S. Desai is presented.

Soil is a material which is weak in tension; however, different materials such as geotextiles are used to address this inadequacy. In recent years more than one million square metres of geotextiles were used for reinforcing soil. Nevertheless, there are several significant problems associated with geotextiles, such as creep, low modulus of elasticity and susceptibility to aggressive environments. Carbon fibre reinforced polymer (CFRP) was introduced over two decades ago to the field of structural engineering and it can also be used in geotechnical engineering. CFRP has all the benefits associated with geotextiles and it boasts a higher strength, higher modulus, no creep and reliability in aggressive environments. In this investigation, the interface properties of CFRP-sand and fine sand were investigated using the pull-out test. The pull-out test device was designed and assembled using a triaxial loading device and a direct shear device. In the pull-out test, the normal force applied by the triaxial loading and pull-out force is applied by a direct shear device. CFRP samples were prepared in the lab. Precast and cast-in-place samples were tested. The pull-out force and corresponding displacements of each of the materials were recorded and compared. [ABSTRACT FROM AUTHOR]