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1.
Implicit integration under mixed controls of a breakage model for unsaturated crushable soils 
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下载免费PDF全文 This paper discusses a series of stress point algorithms for a breakage model for unsaturated granular soils. Such model is characterized by highly nonlinear coupling terms introduced by breakage‐dependent hydro‐mechanical energy potentials. To integrate accurately and efficiently its constitutive equations, specific algorithms have been formulated using a backward Euler scheme. In particular, because implementation and verification of unsaturated soil models often require the use of mixed controls, the incorporation of various hydro‐mechanical conditions has been tackled. First, it is shown that the degree of saturation can be replaced with suction in the constitutive equations through a partial Legendre transformation of the energy potentials, thus changing the thermomechanical state variables and enabling a straightforward implementation of a different control mode. Then, to accommodate more complex control scenarios without redefining the energy potentials, a hybrid strategy has been used, combining the return mapping scheme with linearized constraints. It is shown that this linearization strategy guarantees similar levels of accuracy compared with a conventional strain–suction‐controlled implicit integration. In addition, it is shown that the use of linearized constraints offers the possibility to use the same framework to integrate a variety of control conditions (e.g., net stress and/or water‐content control). The convergence profiles indicate that both schemes preserve the advantages of implicit integration, that is, asymptotic quadratic convergence and unconditional stability. Finally, the performance of the two implicit schemes has been compared with that of an explicit algorithm with automatic sub‐stepping and error control, showing that for the selected breakage model, implicit integration leads to a significant reduction of the computational cost. Such features support the use of the proposed hybrid scheme also in other modeling contexts, especially when strongly nonlinear models have to be implemented and/or validated by using non‐standard hydro‐mechanical control conditions. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
2.
Chemo‐mechanics of cemented granular solids subjected to precipitation and dissolution of mineral species 下载免费PDF全文
下载免费PDF全文 This paper studies the chemo‐mechanics of cemented granular solids in the context of continuum thermodynamics for fluid‐saturated porous media. For this purpose, an existing constitutive model formulated in the frame of the Breakage Mechanics theory is augmented to cope with reactive processes. Chemical state variables accounting for the reactions between the solid constituents and the solutes in the pore fluid are introduced to enrich the interactions among the microstructural units simulated by the model (i.e., grains and cement bonds). Two different reactive processes are studied (i.e., grain dissolution and cement precipitation), using the chemical variables to describe the progression of the reactions and track changes in the size of grains and bonds. Finally, a homogenization strategy is used to derive the energy potentials of the solid mixture, adopting probability density functions that depend on both mechanical and chemical indices. It is shown that the connection between the statistics of the micro‐scale attributes and the continuum properties of the solid enables the mathematical capture of numerous mechanical effects of lithification and chemical deterioration, such as changes in stiffness, expansion/contraction of the elastic domain, and development of inelastic strains during reaction. In particular, the model offers an interpretation of the plastic strains generated by aggressive environments, which are here interpreted as an outcome of chemically driven debonding and comminution. As a result, the model explains widely observed macroscopic signatures of geomaterial degradation by reconciling the energetics of the deformation/reaction processes with the evolving geometry of the microstructural attributes. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
3.
The paper presents a strainhardening constitutive model for unsaturated soil behaviour based on energy conjugated stress variables in the framework of superposed continua. The proposed constitutive law deals with hydro‐mechanical coupling phenomena. The main purpose is to develop within a consistent framework a model that can deal with possible mechanical instabilities occurring in partially saturated materials. The loss of capillary effects during wetting processes can, in fact, play a central role in unstable processes. Therefore, it will be shown that the bonding effects due to surface tensions can be described in a mathematical framework similar to that employed for bonded geomaterials to model weathering or diagenesis effects, either mechanically or chemically induced. The results of several simulations of common laboratory tests on partially saturated soil specimens are shown. The calculated behaviour appears to be in good qualitative agreement with that observed in the laboratory. In particular it is shown that volumetric collapse phenomena due to hydraulic debonding effects can be successfully described by the model. Finally, it will be highlighted the ability of the model to naturally capture the transition to a fully saturated condition and to deal with possible mechanical instabilities in the unsaturated regime. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
4.
Acta Geotechnica - Structured granular materials exhibit strongly anisotropic mechanical behaviours resulting from the directional properties of their microstructural components such as grain... 相似文献
5.
The mathematical properties of diffuse and localized failure modes in fluid‐saturated sands are investigated. The granular medium is modeled as an elastoplastic solid, and a recently proposed set of scalar indices, here referred to as moduli of instability, is used to identify the onset of potential bifurcations of the incremental response. First, the analytical properties of these moduli are discussed, stressing their dependence on the kinematic constraints associated with the imposed deformation modes. Then, by using an elastoplastic model for sands, drained and undrained loading paths are simulated under axisymmetric, plane‐strain and simple shear conditions. For each deformation mode, the instability moduli are computed and monitored throughout the simulations, with the purpose of elucidating the consequences of changes in control conditions. In addition, it is illustrated that suitable linear transformations allow the same strategy to be used to perform drained or undrained shear band analyses and predict the interval of possible band inclinations. The final comparison against literature experiments on loose Hostun sand shows that the instability moduli are indicators of the loss of resistance against specific modes of deformation. As a result, they can be used to identify and explain a number of failure mechanisms that can be commonly observed in experiments. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
6.
Simulation of cyclic strength degradation of natural clays via bounding surface model with hybrid flow rule 下载免费PDF全文
下载免费PDF全文 Strength loss of natural clays subjected to seismic loading is a critical factor contributing to earthquake‐induced ground failure and associated hazards. This work proposes a bounding surface constitutive law to simulate cyclic strength degradation of natural clays resulting from the loss of structure and attendant accumulation of excess pore pressures. The proposed model employs an enhanced plastic flow rule that can simulate accurately the development of pore pressure and explicitly incorporates soil structure effects. The validation of the model with reference to the experimental evidence available for 3 structured clays shows that with a single set of parameters the proposed model can reasonably represent the mechanical behavior of natural clays under various loading conditions (1D compression, monotonic shearing in compression and extension, cyclic loading, and postcyclic shearing). Particularly, its satisfactory performance in terms of quantification of cyclic strength degradation encourages the use of the model in simulating boundary value problems related to the stability of geotechnical facilities under earthquakes. 相似文献
7.
Giuseppe Buscarnera 《Acta Geotechnica》2014,9(2):313-327
The paper investigates the mathematical structure of plasticity models for unsaturated soils and provides a strategy to capture the loss of uniqueness of the incremental solution upon loading and/or wetting paths. To derive bifurcation conditions in simple analytical form, the analysis is restricted to isotropic stress states. This choice has allowed the inspection of the most common classes of constitutive models through a unified notation, as well as the study of different forms of coupling between plasticity and state of saturation. It is shown that, similar to saturated soil plasticity, the loss of admissibility of the plastic solution is governed by critical values of the hardening modulus. At variance with the classical case, however, these moduli can be positive even if the plastic flow rule is associated (bifurcation in the hardening regime). The paper shows that such non-trivial features derive from hydro-mechanical coupling, i.e. they depend on the approach used to reproduce suction effects and evolving retention properties. In other words, although the problem of loss of uniqueness affects all classes of plasticity models for unsaturated soils, different constitutive assumptions may not have the same outcome in terms of bifurcation potential. As a result, new concepts are introduced to compare the mathematical robustness of the different constitutive approaches, as well as to interpret their predictions in the light of precise bifurcation criteria. 相似文献
8.
Moscariello Mariagiovanna Chen Yanni Cuomo Sabatino Buscarnera Giuseppe 《Acta Geotechnica》2023,18(2):791-809
Acta Geotechnica - The simple shear response of air-fall volcanic (pyroclastic) soils under both saturated and unsaturated conditions is interpreted through an elastoplastic constitutive model with... 相似文献
9.
This paper presents a theoretical framework to interpret the inception of unstable undrained creep in quasi‐saturated soils. For this purpose, the effect of gas bubbles occluded in the fluid phase is embedded into an augmented compressibility of the fluid mixture, while the mechanical characteristics of the solid skeleton have been simulated through a viscoplastic strain‐hardening model. This constitutive framework has been been used to formulate a theoretical platform able to detect runaway failures resulting from extended stages of undrained creep. It is shown that the conditions identifying the onset of spontaneous accelerations are governed by the same stability index associated with the initiation of static liquefaction. At variance with soils saturated by incompressible fluids, the conditions for undrained instability are altered by the appearance of the Skempton coefficient B, thus reflecting the beneficial effect of the fluid compressibility and its ability to decrease the liquefaction potential. The capabilities of the theory are verified through a sequence of undrained creep simulations showing the transition from stable to unstable behavior resulting from an increase of the degree of saturation. The proposed findings provide a conceptual framework to interpret the effects of gas bubbles in loose soils, as well as to assess effectiveness and longevity of liquefaction mitigation strategies based on desaturation technologies. 相似文献
10.
This paper discusses the formulation and the numerical performance of a fully implicit algorithm used to integrate a rate-dependent model defined within a breakage mechanics framework. For this purpose, a Generalized Backward Euler (GBE) algorithm has been implemented according to two different linearization strategies: The former is derived by a direct linearization of the constitutive equations, while the latter introduces rate effects through a consistency parameter. The accuracy and efficiency of the GBE algorithm have been investigated by (1) performing material point analyses and (2) solving initial boundary value problems. In both cases, the overall performance of the underlying algorithm is inspected for a range of loading rates, thus simulating comminution from slow to fast dynamic problems. As the viscous response of the breakage model can be recast through a viscous nucleus function, the presented algorithm can be considered as a general framework to integrate constitutive equations relying on the overstress approach typical of Perzyna-like viscoplastic models. 相似文献