Dr. Ivan P. Damians (B.Eng., B.A., M.Sc., M.A., Ph.D.)

Polymeric strip reinforced soil walls require a practical method to fix the reinforcement tail-ends in the soil backfill during construction to ensure adequate anchorage and to avoid any slack along the linear reinforcement elements. A number of different techniques are currently used depending on the reinforcement type, arrangement and the contractor. This paper reports the results of a series of numerical simulations that were carried out on an idealized 6 m-high wall with precast partial height facing panels. A different reinforcement pre-tension load was applied to the layers in each simulation case. The results of numerical simulations include the reinforcement axial load distribution, vertical facing load and end-of-construction facing alignment plotted as a function of the reinforcement layer depth location and applied pre-tension load. The results demonstrate that the magnitude of pre-tensioning has a significant effect on wall performance for walls subjected to operational (working stress) conditions at end of construction.Postprint (published version

This paper extends the numerical parametric study previously reported by the writers for the vertical load distribution and vertical gap compression between facing panel units in steel reinforced soil walls ranging in height from 6 m to 24 m. The presented study demonstrates how gap compression and magnitude of vertical load transmitted between horizontal joints are influenced by joint location along the height of the wall, joint compressibility, and backfill, and foundation soil stiffness. The charts provided can be used to make a preliminary estimate of the number and type (stiffness) of the bearing pads to ensure a target minimum gap thickness at the end of construction, demonstrate the relative influence of wall height and different material component properties on vertical load levels and gap compression, or used as a benchmark to test numerical models used for project-specific design.

In a repository for radioactive waste, corrosion of metallic materials leads to the formation of hydrogen and other gases. If the gas production rate exceeds the gas diffusion rate within the pores of the surrounding material, a discrete gas phase forms. Gas pressure will then continue to accumulate until its pressure becomes sufficient to exceed the entry pressure of the surrounding material.

The role of temperature and relative humidity in long-term mechanical and chemical degradation of polyester fibres due to hydrolysis and creep is well documented. This study presents the results of a thermo-hydraulic 2D finite-element model used to estimate the magnitude and distribution of in situ temperature, relative humidity, and degree of saturation in the backfill of reinforced soil walls (RSWs) due to changes in atmospheric boundary conditions. Boundary conditions for in-air temperature, relative humidity and daily precipitation were taken from weather databases for continental, Mediterranean, desert, and tropical climates. Scenarios with different water tables, and permeable or impermeable zones around the reinforced soil zone were analyzed. Numerical outcomes show that mean in-soil temperature values can be related to the mean annual atmospheric value for each geographical location, with relevant fluctuations limited to the first 3 m of distance from the vertical and horizo...

This study describes the results of a series of 2D finite element method (FEM) numerical models of 6 m high back-to-back reinforced soil walls using the geotechnical software PLAXIS. These structures are used to support embankments, especially for bridge abutment approaches. The quantitative influence of problem geometry, strip pre-tensioning, strip type, and surcharging on horizontal displacements, development of soil shear and plastic zones, lateral earth pressure, and reinforcement loads is presented. The numerical results demonstrate how this type of reinforced soil walls perform jointly at a certain distance of interaction between the two opposite walls. The walls of the two opposing sides clearly interact with each other when they are close enough and with an overlapping reinforcement layout. Pre-tensioning load can contribute to achieving vertical wall-facing alignment at the end of construction. Using perforated/holed strips, the tensile loads at the end of construction were...

Soil-facing mechanical interactions play an important role in the behavior of earth retaining walls. Generally, numerical analysis of earth retaining structures requires the use of interface elements between dissimilar component materials to model soil-structure interactions and to capture the transfer of normal and shear stresses through these discontinuities. In the finite element method PLAXIS software program, soil-structure interactions can be modelled using “zero-thickness” interface elements between the soil and structural components. These elements use a strength/stiffness reduction factor that is applied to the soil adjacent to the interface. However, in some numerical codes where the zerothickness elements (or other similar special interface elements) are not provided, the use of continuum elements to model soil-structure interactions is the only option. The continuum element approach allows more control of the interface features (i.e., material strength and stiffness prop...

This report summarizes the scope and conclusions of a 3D numerical modelling analysis of mechanically stabilized earth (MSE) walls constructed with concrete panels and strip reinforcement. These systems pose numerical challenges as a result of the discontinuous reinforcement arrangement which suggest the necessity on the 3D strategies instead of 2D modelling to determine and to fit its actual intrinsic behaviour.

ABSTRACT The paper describes the results and lessons learned using a FEM model to simulate quantitative performance features of the Minnow Creek steel-strip reinforced soil wall structure located in the United States. The Minnow Creek Wall structure was constructed and instrumented in 1999. It is a unique case study because of the comprehensive measurements that were taken to record a wide range of wall performance features. Two different constitutive models for the soil were used (a linear-elastic Mohr-Coulomb model and hardening soil model with a Mohr-Coulomb failure criterion), and numerical outcomes were compared with physical measurements. The numerical results were shown to be sensitive to boundary conditions assumed at the toe of the wall. The generally encouraging agreement between physical and numerically predicted results gives confidence that commercial FEM software packages can be useful for the analysis and design of these types of structures, provided that care is taken in the selection of input parameters.

This document provides a summary of the different topics presented at the Special Session organized by the International Geosynthetics Society (IGS) Technical Committee on Soil Reinforcement (TC-R). This Special Session brings together very interesting studies regarding soil reinforcement in the field of geosynthetics. Studies presented include topics both from theoretical and practical points of view of reinforcement geosynthetics including general products and applications, cases studies on road embankments under challenging site boundary conditions, research on deterministic and probabilistic design of reinforced fills over voids, numerical analysis of reinforced soil wall structures, encased granular column technique, and geosynthetic-reinforced bridge abutment behavior.

ABSTRACT: In this work, the suitability of several meshing strategies to optimize the CPU time consumption is investigated. The mesh sensitivity strategy is established by applying the basic framework of a coupled hydro-gas-mechanical 3D FEM numerical model to simulate the tests in terms of types of the elements, number of elements and nodes to quantify the influence of different meshes on the accuracy of the test results with regard to optimization of the CPU time consumption. In this study, the problem is represented and the performance and calculation time of both element types and mesh size in the utilized 3D FEM model are checked. To achieve this, both tetrahedral and hexahedral meshes and their refinement/coarsening are generated. Then the performance of the element types and sizes on the test results are compared. This is a main issue for modelling gas injection through clay-based engineered isolation barriers that requires clear up-scaled tests due to full-scale experiments....

<p>The construction and operational phases of a deep geological repository imply potential perturbations of the host rock, so-called Repository Induced Effects (RIE). Amongst them, spent fuel and high level waste (SF/HLW) produce decay heat even after long times of cooling, which may impair the long-term safety of the Engineered Barrier System and of the geological barrier. The Opalinus Clay (OPA), is currently being assessed as host rock for the deep geological repository in Switzerland. OPA is an indurated clay of Jurassic age (ca. 180 My), whose main features are (1) a very low hydraulic conductivity, (2) an excellent retention capacity for dissolved radionuclides, and (3) a significant self-sealing capacity.</p><p>The on-going Full-scale Emplacement (FE) Experiment at the Mont Terri Underground Rock Laboratory simulates, as realistically as possible, the construction, waste emplacement, backfilling and early-stage post-closure evolution of a single SF/HLW emplacement tunnel in OPA, using heaters instead of disposal canisters. The main goal of the FE experiment is the investigation of RIE on the host rock (and, to a lesser extent, on the the backfill material) at true scale and the validation of existing coupled thermo-hydro-mechanical (THM) models. In this context, Nagra has developed a new RD&D initiative, i.e., the FE modelling Task Force (FE-M TF), which involves three modelling teams with corresponding software packages (Code Aster, Code Bright and OpenGeoSys). So far, the TF has defined three main tasks:</p><ul><li>Code comparison and calculation verification: the TF designed a simplified (though realistic) 3D conceptual model of the FE experiment that includes the actual geometry of the main elements, materials and phases of the FE experiment, including tunnel excavation and ventilation. Such conceptual model was implemented by the modelling teams. Finally, code outputs were analysed and compared by the TF.</li> <li>Back-analyses of THM-observations in the host rock: monitoring data from radial<br>and oblique boreholes around the backfilled FE tunnel are used for model calibration,<br>including the derivation of parameter best estimates and inherent uncertainties, and model</li> <li>Model validation in the context of a prediction-evaluation exercise: the evolution<br>of the THM conditions in the rock in response to a change of thermal loads (e.g., increase/decrease of heater output) will be predicted using the calibrated models. Finally, model predictions will be validated in the near future using the acquired measurements.</li> </ul><p>This presentation summarizes the current status of Tasks 1 and 2 and the path forward to Task 3.</p>

Soil-facing mechanical interactions play an important role in the behavior of earth-retaining walls. Generally, numerical analysis of earth-retaining structures requires the use of interface elements between dissimilar component materials to model soil–structure interactions and to capture the transfer of normal and shear stresses through these discontinuities. In finite element method software programs, soil–structure interactions can be modeled using “zero-thickness” interface elements between the soil and structural components. These elements use a strength/stiffness reduction factor that is applied to the soil adjacent to the interface. However, in some numerical codes where the zero-thickness elements (or other similar special interface elements) are not available, the use of continuum elements to model soil–structure interactions is the only option. The continuum element approach allows more control of the interface features (i.e., material strength and stiffness properties), ...

ABSTRACT The choice of structure element to simulate soil reinforcement and soil-structure interaction details for numerical modelling of mechanically stabilized earth (MSE) walls can have a significant influence on numerical outcomes. Program FLAC (finite difference method) offers three different options (beam, cable and strip) to model the reinforcement and program PLAXIS (finite element method) has only one (“geogrid” element). Both programs use different models and properties to simulate the mechanical behavior of the interface between dissimilar materials. The paper describes the details of the Mohr-Coulomb interface model available in the two software packages to model material interaction and how to select model parameters to give the same numerical outcomes. The numerical results quantitatively demonstrate the conditions that give good agreement between the two programs for the same reinforced soil-structure problem and the situations where they do not. For example, the paper demonstrates that results can be very different depending on the type of structure element used to model horizontal reinforcement layers that are discontinuous in the plane-strain direction. // Le choix des éléments structuraux pour simuler les détails des renforcements de sol et l’interaction s ol-structure pour la modélisation numérique des murs en sol renforcé, peut avoir une influence significative sur les résultats numériques. Le programme FLAC (méthode des différences finis) offre trois différentes options (poutre, câble et languette) pour modéliser le renforcement et le programme PLAXIS (méthode des éléments finis) n’en n’a qu’un seul (l’élément « géogrille »). Les deux programmes utilisent différents modèles et propriétés pour simuler le comportement mécanique de l’interface entre des matériaux dissimilaires. L’article décrit les détails du modèle d’interface de Mohr-Coulomb disponible dans les deux logiciels pour modéliser l’interaction entre les matériaux et décrit comment choisir les paramètres du modèle pour obtenir les mêmes résultats numériques. Les résultats numériques démontrent quantitativement les conditions qui mènent à un bon accord entre les deux programmes, pour le même problème d’interaction sol renforcé–structure, et les situations où il n’y a pas accord. Par exemple, l’article démontre que les résultats peuvent être très différents dépendant du type d’élément structural utilisé pour modéliser des couches derenforcement horizontales qui sont discontinues dans la direction des déformations plane

ABSTRACT The choice of structure element to simulate soil reinforcement and soil–structure interaction details for numerical modelling of mechanically stabilized earth (MSE) walls can have a significant influence on numerical outcomes. Program FLAC (finite difference method) offers three different options (beam, cable and strip element) to model the reinforcement and program PLAXIS (finite element method) has two (beam and geogrid element). Both programs use different models and properties to simulate the mechanical behaviour of the interface between dissimilar materials. The paper describes the details of the linear elastic Mohr–Coulomb interface model available in the two software packages to model material interaction and how to select model parameters to give the same numerical outcomes. The numerical results quantitatively demonstrate the conditions that give good agreement between the two programs for the same steel strip reinforced soil–structure problem and the situations where they do not. For example, the paper demonstrates that results can be very different depending on the type of structure element used to model horizontal reinforcement layers that are discontinuous in the plane-strain direction.

ABSTRACT Most geosynthetic and metallic reinforced soil walls are designed assuming that the wall foundation is rigid and/or does not influence the magnitude and distribution of reinforcement loads under operational conditions. This assumption may not apply to walls constructed over compliant (compressible) foundations. This paper describes the results of a series of numerical simulations that were carried out on idealized 3?6, 6, and 9 m-high modular block walls seated on foundations having four different compressibility values. The walls were constructed with two reinforcement materials having very different stiffness values but the same tensile strength. The results of simulations show that as foundation stiffness decreases, reinforcement loads increase. However, for the two reinforcement materials in this study, the influence of axial stiffness of the reinforcement had a greater effect on wall performance than the foundation stiffness for walls subjected to operational (working stress) conditions at end of construction.