Mashayekhi, M.,
Kaliakin, V.N.,
Meehan, C.L.,
Adams, M.T.,
Nicks, J.E. Publication Date: 2019
Geotechnical Special Publication (08950563)2019(GSP 310)pp. 20-29
Structural backfills are one of the primary construction materials for critical transportation infrastructure projects such as geosynthetic reinforced soil structures, mechanically stabilized earth walls, railway beds, and other earthworks. A variety of approaches exists to numerically characterize the behavior of the well-graded and open-graded gravel aggregates that are commonly used in structural backfills. However, over-simplifications in modeling the behavior of such aggregates can omit some key aspects of their behavior, especially at very low effective stress levels. This paper describes the use of the single hardening model to simulate the behavior of structural backfills. The model is validated against a series of triaxial test results to accurately simulate the behavior of aggregate at low and intermediate levels of confinement. Modifications to the SHM are proposed that improve its predictive capabilities with respect to the deformation behavior of structural backfills. © 2019 American Society of Civil Engineers.
Publication Date: 2018
International Journal for Numerical and Analytical Methods in Geomechanics (03639061)42(3)pp. 469-487
Improved, microfabric-inspired rotational hardening rules for the plastic potential and bounding surfaces associated with the generalized bounding surface model for cohesive soils are presented. These hardening rules include 2 new functions, fη and fI0, that improve the simulation of anisotropically consolidated cohesive soils. Three model parameters are associated with the improved hardening rules. A detailed procedure for obtaining suitable values for these parameters is presented. The first 2 parameters affect the simulation of constant stress ratio loading where, because of the presence of fη, the third parameter is inactive. The second new function, fI0, accelerates the rotation of the plastic potential and bounding surfaces during shearing, which is particularly important for overconsolidated soils tested in extension. This paper also describes the proper manner in which to define the inherent anisotropy. This seemingly straightforward test has rarely been discussed in sufficient detail. Copyright © 2017 John Wiley & Sons, Ltd.
Publication Date: 2018
Transportation Infrastructure Geotechnology (21967202)5(3)pp. 250-286
The Generalized Bounding Surface Model (GBSM) synthesizes many previous bounding surface models for cohesive soils and improves upon their predictive capabilities. Following an overview of the GBSM and its extension to account for non-isothermal conditions, the predictive capabilities of the model are assessed. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.
The concept of rotational hardening (RH) was introduced into constitutive model formulations in order to rotate a yield or bounding surface from the isotropic axis during either anisotropic consolidation or shearing. To properly account for the evolution of stress induced anisotropy during shearing, a suitable RH rule must be used. An improved RH rule is presented in this work. Although it incorporates aspects of several previous formulations, the improved RH rule includes provisions that allow it to more accurately simulate the response of anisotropically consolidated cohesive soils. This is especially true for overconsolidated specimens tested in extension. It was found that in order to properly match the experimental effective stress paths in such tests, it is necessary to accelerate the pace of rotation of the plastic potential towards the critical state line in extension; the higher the overconsolidation ratio, the faster should be the pace of rotation. © ASCE.
The prediction of stresses, deformations and temperature as a function of time in a material subjected to simultaneous thermal and mechanical loading is one of the most challenging and complex problems in engineering mechanics. In the field of Geomechanics a number of important problems exist that necessitate the realistic prediction of time-dependent thermal-mechanical behavior. Thermal-mechanical analyses of soils are complicated by the nature of these materials. Soils consist of a porous skeleton whose voids are filled with fluid and gas. Consequently, soils are nonhomogeneous materials. Macroscopically such materials exhibit an anisotropic, inelastic, path-dependent, strain hardening (and softening), time-, rate- and temperaturedependent behavior. To further complicate matters, the thermal properties of such materials are not as well known as those for othermaterials such as metals. The variability in a soil's composition and subsequent degrees of thermal and mechanical dependency further increase the complexity of the thermo-mechanical behavior of such material. Finally, natural soils are also subject to sample disturbance that makes the task of representative testing all the more difficult. Local variations in soil composition often preclude the obtaining of reproducible test results, and thus impose limitations on the confidence associated with the analytical description of the soil behavior. This chapter briefly discusses the rudimentary microscopic and physicochemical aspects associated with saturated cohesive soils. This is followed by a discussion of the macroscopically observed time- and temperature-dependent behavior of such soils. Finally, a combined and coupled thermo-elastoplastic-viscoplastic framework for modeling the anisotropic, time-, rate- and temperature-dependent behavior of cohesive soils in the context of a bounding surface formulation is proposed. © 2014 Nova Science Publishers, Inc. All rights reserved.
