Constitutive Model For Geomaterials Research Articles

AN ELASTO-VISCOPLASTIC MODEL FOR SOFT SEDIMENTARY ROCK BASED ON TIJ CONCEPT AND SUBLOADING YIELD SURFACE

In this paper, an elasto-viscoplastic constitutive model with strain softening is developed for soft sedimentary rock using a newly proposed evolution equation for subloading yield surface originally invented by Hashiguchi (1980). In the model, associated flow rule is adopted and tij concept, which can take into consideration the influence of intermediate stress on deformation and strength of geomaterials, is used. In the model, as is the same as Cam-clay model, plastic volumetric strain is used as hardening parameter, which is widely accepted by the researchers who specialize in the constitutive model for geomaterials. The application of the model to the experimental results of soft sedimentary rock indicates that the model not only can describe the time dependency, such as strain rate dependency and creep, but also the strain softening behavior of geologic materials. The material parameters involved in the model have clear physical meanings and can be easily determined with triaxial compression tests and creep tests.

Constitutive Modelling of Geomaterials

Constitutive Modelling of Geomaterials

A novel constitutive model for geomaterials in hyperplasticity

This paper proposes a new constitutive model for geotechnical materials that consists two basic constitutive functions, the free energy function and the dissipation rate function, within the framework of hyperplastic theory. This free energy function is capable of describing the pressure-dependent elastic behavior of soils. The new constructed dissipation rate function accounts for the frictional mechanism of energy dissipation. Based on this dissipation rate function, the non-associated flow rule can be obtained. Furthermore, the convexity of the yield surface that is derived from the dissipation rate function is proved. Predictions of the behavior of a soil sample using this new constitutive model agree well with triaxial test data under drained and undrained conditions.

Constitutive Modeling of Geomaterials and Interfaces with Applications

Constitutive Modeling of Geomaterials and Interfaces with Applications

Constitutive modelling of compaction localisation in porous sandstones

Porous sandstones exhibit localised modes of failure in the form of shear or compaction bands. In particular, shear localisation is associated with brittle behaviour under low confining pressures, while under increasing confining pressures, their failure gradually becomes more ductile with the onset and propagation of compaction bands. The orientation and size of these localisation bands vary with the loading and material properties. As a consequence, a correct description of the behaviour of porous sandstones must take into account all these characteristics of localised failure. As a departure from existing approaches that take into account the orientation of localisation band, we present in this study a new approach to incorporate both size and orientation of localisation zone in constitutive models for geomaterials. Based on this approach, a breakage mechanics constitutive model is enhanced with localised mode of failure and used for the post-localisation analysis of porous sandstones. The concepts together with technical details, and numerical results are presented to show the potentials of the new approach.

A unified thermoplastic/viscoplastic constitutive model for geomaterials

Research on the effect of temperature changes on the behaviour of geomaterials has become increasingly important in recent years. This growing interest is partially due to the recent development of high-level nuclear waste disposals. Because of the complex influence of temperature in these areas, it is necessary to understand the effects of temperature on rock-like materials and use the appropriate constitutive equations to numerically model these phenomena. In this paper, a thermoplastic/viscoplastic constitutive model is developed for this purpose. The model includes thermal softening, the evolution of the yield functions with temperature, and the effects of temperature on the time-dependent behaviour. The model performance is demonstrated by some simple test cases on Tournemire and Bure clayey rocks including triaxial compression tests and creep tests under constant temperatures. The numerical results are discussed using experimental data, which demonstrate that the model can reproduce the overall behaviour of this type of materials under deviatoric loads and non-isothermal conditions.

Teruo Nakai: Constitutive modeling of geomaterials, principles and applications

Teruo Nakai: Constitutive modeling of geomaterials, principles and applications

A Mathematical Approach to Establishing Constitutive Models for Geomaterials

The mathematical foundation of the traditional elastoplastic constitutive theory for geomaterials is presented from the mathematical point of view, that is, the expression of stress-strain relationship in principal stress/strain space being transformed to the expression in six-dimensional space. A new framework is then established according to the mathematical theory of vectors and tensors, which is applicable to establishing elastoplastic models both in strain space and in stress space. Traditional constitutive theories can be considered as its special cases. The framework also enables modification of traditional constitutive models.

How to connect two scales of behaviour in constitutive modelling of geomaterials

Localised failure of geomaterials involves deformation at two scales: a narrow localisation zone and the surrounding bulk. The behaviour associated with both scales should be properly taken into account in the development of constitutive models. This article presents a general constitutive modelling framework to connect these two scales, each of which is associated with a different stage of the material behaviour. It is demonstrated how this approach can be applied to any geomaterial model and how it could help obtain solutions independent of the spatial discretisation in numerical analysis.

Special Section on Advanced Modeling and Numerical Simulations in Geomechanics

This special section of the International Journal of Geomechanics contains selected papers that are based on the presentations at the GeoHunan International Conference: Challenges and Recent Advances in Pavement Technologies and Transportation Geotechnics, held in Changsha, Hunan, China, on August 3–6, 2009. The subject of geomechanics has come a long way in developing constitutive models for geomaterials, including nontraditional materials. Yet, there are complex geomechanics problems that do not have well-defined constitutive models and solutions. Recently, advanced modeling and numerical simulation techniques such as neural network, bound theorem, and centrifuge modeling have been employed to solve some of those geomechanics problems. Owing to the rapid expansion in the use of computer software, nonlinear numerical analysis or neural network modeling has become very popular among researchers and practicing engineers in recent years. Although theoretical models have been around for a long time, it has always been challenging to develop such models. Recently, small-scale centrifuge-based simulations have shown a promising capability of modeling prototype geostructures without a gravityinduced in situ stress field. This special section contains six full-length papers covering such advanced modeling and numerical simulations, different from traditional constitutive modeling, in geomechanics. The paper contributed by Xiang et al. discusses settlement prediction on a chimney foundation by a neural network. In their work, seven models with different input series were developed. The optimal model was determined by comparing the forecasting performance. Xiao et al. carried out numerical simulations of a single pile in expansive soil and extensively studied the load transfer mechanism and soil-pile interaction. Chen and Yu present a study on centrifuge modeling, in which staged construction on a reinforced lime-stabilized embankment was simulated by spinning the model at various g-levels. Centrifuge test results were used to verify and validate their numerical analysis. A comprehensive literature review on constitutive modeling of unsaturated soil is presented by Zhang and Li. Some limitations in the framework of the Barcelona Basic Model are discussed, and a new approach is proposed to overcome the limitations. Fu et al. investigated the compressive behavior of anchored rock masses through a series of physical model tests. The test results were compared with specimens without anchor bolts. It was concluded that the improvement attributable to vertical bolts is more effective. Zhao et al. employed an upper bound limit analysis to evaluate the ultimate pullout capacity of horizontal shallow plate anchors. Dilation and nonlinear behavior of soil was found to have profound effects on the ultimate pullout capacity.

Identification technology based on constitutive model database of geotechnical material

Constitutive model back analysis is an important aspect and difficult point in geo-material back analysis, in which the identification of geo-material constitutive model is precondition and foundation of constitutive model back analysis. Based on the present circumstances about the model identification methods of geo-material constitutive researching, it begins with the fundamental principle of identification, puts forward the researching train of thought taking the geo-material constitutive model database as a platform, combining several identification algorithms.

Identification of Constitutive Model for Geo-Materials Using Bionics Algorithm

Identification of Constitutive Model for Geo-Materials Using Bionics Algorithm

Constitutive Modeling of Geomaterials

Recent advancements in computer technology have paved the way for solving boundary value problems that could not be solved in the past due to a lack of affordable computing power. However, among other things, the accuracy of boundary value predictions hinges critically on the accuracy with which the constitutive behavior of the material is modeled. While the past several decades have seen impressive progress in the area of constitutive model development, many topics still remain challenging and new methods are continually being proposed. The objective of this special issue is to provide an avenue for presenting some of the recent developments in one place. While there are differences between their behaviors, most geomaterials ~soils, concrete, rocks, etc.! have a lot in common. For example, geomaterials contain pores that are fully or partially filled with fluids, requiring poromechanical behavior to be modeled. Many of the geomaterials exhibit significant creep ~e.g., clays, cement, concrete, asphalt concrete, etc.!. Most importantly, their behaviors are pressuredependent. Concepts developed for modeling one geomaterial can be used directly or with modifications to model another geoma-

Penetration into low-strength (23 MPa) concrete: target characterization and simulations

A combined experimental, analytical, and computational research and development program investigates the penetration of steel projectiles into low-strength concrete. Laboratory-scale material property tests conducted at the US Army Waterways Experiment Station on the concrete provide the data used in parameter estimation for a geomaterial constitutive model. The experiments and the model are described as well as the procedure used to fit the material model to the experimental data. The model accurately reproduces the data and predicts experimental results not used in the evaluation of model constants. The model, used in conjunction with an explicit transient dynamic finite element code, accurately predicts deceleration and depth of penetration of 3 CRH ogive-nosed 4340 steel penetrators.

Constitutive Modelling of Geomaterials

Constitutive Modelling of Geomaterials

Two theoretically consistent methods for analysing triaxial tests

Abstract Constitutive models for geomaterials are frequently developed and calibrated on the basis of element tests. Prior to the analysis of element tests a suitable set of work-conjugated stress and strain measures has to be selected. The paper points out that the traditional analysis of triaxial tests is theoretically inconsistent as finite and infinite strain measures are mixed in the analysis. Therefore, two theoretically consistent methods are proposed and examined for the analysis of triaxial tests. These three methods affect strain-dependent material parameters differently. The effect is analysed using key geotechnical parameters and an advanced constitutive model.

Constitutive modeling of geomaterials from non-uniform material tests

Abstract As the name implies, a non-uniform material test has a non uniform distribution of stresses and strains within the specimen. An example is a triaxial test with end friction. Unlike the conventional material tests, points in the specimen in a non-uniform material test are subjected to widely varying stress paths. In this paper a method to extract the material constitutive behavior from a non-uniform material test is presented. This method employs the use of a neural network material model in a finite element analysis. The measured boundary forces and displacements are applied in the finite element analysis to generate the input and output vectors for training the neural network material model. This method has been applied to a series of triaxial compression tests with end friction on sand.