Modelling the effect of in-soil temperature and relative humidity on performance of PET strap soil reinforcement products

Els materials de reforç de polièster (PET) ara s'utilitzen de manera rutinària com a reforç del sòl per a les parets de terra estabilitzada mecànicament. L'important paper de la temperatura i la humitat relativa en la degradació química de les fibres de PET a causa de la hidròlisi està ben documentat en la literatura. Es pot esperar que la força i la rigidesa de les fibres del polièster disminueixin amb l'augment de la temperatura i en presència d'humitat. Això té implicacions pràctiques per a la selecció del factor parcial per a la degradació química i la deformació a llarg termini que s'utilitza en el disseny de l'estat de límit d'estabilitat intern en les parets de la MSE. El nucli multifilament PET de les corretges està protegit contra el dany d'instal·lació i la humitat per una beina de polietilè. Aquest estudi presenta els resultats d'anàlisis utilitzant simulacions numèriques que es van dur a terme per estimar, en primer lloc, la temperatura i la humitat relativa canvien en el sòl respecte a les diferents propietats terrestres i les condicions de frontera atmosfèrica, i en segon lloc, els canvis de força i rigidesa temporal en les corretges simulades de PET enterrats col·locades en diferents ambients del sòl, mentre que sotmeses a diferents càrregues tensives i temperatures. Encara que no hi ha cap mesura disponible en el lloc, els resultats modelats es comparen i es troben consistents amb la investigació anterior similar sobre les distribucions de temperatura en el sòl. Finalment, es presenta un primer acostament a un termohidromecànic totalment acoblat (THM). El comportament de creep està adequadament modelat amb tires de PET simples simulades però no en el model complet de la paret MSE.Los materiales de refuerzo de fibras de poliéster (PET) se utilizan actualmente de forma rutinaria como refuerzo del suelo para los muros de tierra mecánicamente estabilizada (MSE por sus siglas en ingles). El rol de la temperatura y la humedad relativa en la degradación química de las fibras PET debido a la hidrólisis está bien documentado en la literatura. Es de esperar que la rigidez y resistencia de las fibras de poliéster disminuyan con el aumento de la temperatura y en presencia de humedad. Esto tiene implicaciones prácticas para la selección de los factores parciales de degradación química y deformación a largo plazo que se utiliza en el diseño del estado límite de estabilidad interna en los muros MSE. El núcleo de multifilamentos de PET de las correas está protegido contra los daños de la instalación y la humedad por una funda de polietileno. El presente estudio detalla los resultados de los análisis realizados mediante simulaciones numéricas para estimar, en primer lugar, los cambios de temperatura y humedad relativa en el suelo en relación con diferentes propiedades del terreno y condiciones atmosféricas impuestas, y, en segundo lugar, los cambios a lo largo del tiempo en resistencia y rigidez en refuerzos tipo PET simulando diferentes entornos de suelo mientras se someten a variados estados de cargas y temperaturas. Aun cuando no se dispone de mediciones de campo, los resultados modelados son comparados y se encuentran concordantes con investigaciones anteriores con respecto a la distribución de temperaturas en el terreno. Por último, se presenta una primera aproximación a un sistema termo-hidro-mecánico (THM) totalmente acoplado. El comportamiento de fluencia a largo plazo de refuerzos PET es modelado de forma adecuada para elementos individuales, no así dentro del modelo completo del muro MSEPolyester (PET) strap reinforcement materials are now used routinely as soil reinforcement for mechanically stabilized earth (MSE) walls. The important role of temperature and relative humidity on the chemical degradation of PET fibres due to hydrolysis is well documented in the literature. Strength and stiffness of the polyester fibres can be expected to decrease with increasing temperature and in the presence of moisture. This has practical implications for the selection of the partial factor for chemical degradation and long-term deformation that is used in internal stability limit state design in MSE walls. The PET multi-filament core of the straps is protected against installation damage and moisture by a polyethylene sheath. This study presents the results of analyses using numerical simulations that were carried out to estimate, first, the temperature and relative humidity changes in-soil regarding different ground properties and atmospheric boundary conditions, and second, the temporal strength and stiffness changes in simulated buried PET straps placed in different soil environments while subjected to different tensile loads and temperatures. Though no in site measurements are available, modelled results are compared and found consistent with similar previous research regarding in-soil temperature distributions. Finally, a first approach at a fully coupled thermo-hydro-mechanical (THM) is presented. Creep behaviour is adequately modeled withing single simulated PET straps but not on the full MSE wall model

Short-term thermo-mechanical numerical modelling of reinforced soil walls with polyester strap reinforcements

Polyester (PET) materials have become more common as reinforcement solution in reinforced soil walls (RSW). It has been shown that strength and stiffness of geosynthetics products, including PET, is load-, time-, and temperature-dependent. Consequently, the mechanical response of these materials is influenced by in-soil conditions. The present study describes viscoelastic and visco-plastic constitutive formulations used to model PET strap reinforcement layers in thermo-mechanical finite element models. The models are demonstrated using an idealized 15-meter high RSW with concrete facing panels, including loading due to a road at the top of the structure. Reinforcement model parameters were calibrated using laboratory measured data. Analyses include temperature boundary conditions representing a Mediterranean climate for a 1-year period following end of construction. Calculated stress and strain values were in accordance with values found in the literature. The results of this study are a precursor for the long-term modelling of RSWs under operational conditions subjected to changing atmospheric boundary conditions.The authors wish to thank Aaron Kim from GECO Industrial (Korea, Rep.) for providing polymeric strap data from manufacturing quality control records. The authors wish to acknowledge the support of the Department of Civil and Environmental Engineering (DECA) of the Universitat Politécnica de Catalunya�����BarcelonaTech (UPC) and the International Centre for Numerical Methods in Engineering (CIMNE) and the funding received from the Spanish Ministry of Economy and Competitiveness through the “Severo Ochoa Programme for Centres of Excellence in R&D” (CEX2018-000797-S-20-4).Peer ReviewedPostprint (published version

Simplified approach to analyse global stability of reinforced soil walls

Reinforced soil walls (RSW) are a proven alternative to conventional earth retaining structures due to their rapid construction, smaller environmental impact, lower cost, as well as more sustainable social/functional features. Design methods for RSW appear in international codes and guidelines. However, they often do not provide detailed calculations for global stability assessment. Global stability can significantly affect RSW design for specific geometric cases and/or site-specific boundary conditions. Traditional limit equilibrium (LE) methods have the disadvantage of not considering reinforcements and/or require iterations to achieve a safety factor (SF) value. Alternatively, numerical methods can be time consuming for both model generation, particularly for complex geometries, and during calculations. The present study discusses different analytical strategies using limit equilibrium formulations and a numerical finite element method, and proposes a simplified analytical method for global stability analysis based on a three-part wedge failure mechanism, and simple wall conditions.Peer ReviewedPostprint (published version

Influence of numerical model mesh properties on predicted in soil temperature, relative humidity and degree of saturation of reinforced soil structures

Geosynthetic materials are routinely used in soil reinforcement and stabilization applications. They have proven to be an important part of the sustainable solution for reinforced soil walls (RSWs). For RSW constructed with polyester (PET) reinforcement materials, the influence of temperature and relative humidity on the potential chemical and mechanical degradation of PET fibres due to hydrolysis is well documented in the literature. Consequently, in-soil environmental conditions should be accounted for at the time of design. A thermo-hydraulic (TH) finite element model is described in this study and is used to predict changes in soil temperature, relative humidity and degree of saturation due to temporal atmospheric boundary conditions representing a Mediterranean climate. An idealized 15-meter high RSW with concrete facing panels and PET strap reinforcement layers was modelled. Variations in mesh element size, distribution and type were studied. Numerical results showed that differences in temperature, relative humidity and saturation degree were detectable at the near surface. However, practical differences in predicted in-soil behavior due to mesh geometry were judged to be negligible.The authors wish to thank Aaron Kim from GECO Industrial (Korea, Rep.) for providing valuable data for polymeric straps from reliability assessment testing records. The authors wish to acknowledge the support of the Department of Civil and Environmental Engineering (DECA) of the Universitat Politécnica de Catalunya·BarcelonaTech (UPC) and the International Centre for Numerical Methods in Engineering (CIMNE) and the funding received from the Spanish Ministry of Economy and Competitiveness through the “Severo Ochoa Programme for Centres of Excellence in R&D” (CEX2018-000797-S-20-4).Postprint (author's final draft

Modelización del comportamiento de bandas poliméricas de refuerzo en suelos bajo el efecto de la temperatura y humedad

Los materiales de refuerzo de bandas de poliéster (PET) se utilizan actualmente de forma rutinaria como refuerzo del suelo para los estructuras de contención de suelo reforzado. Es de esperar que la resistencia y la rigidez de las fibras de poliéster disminuya con el aumento de la temperatura y en presencia de humedad. Esto tiene implicaciones prácticas para la selección del factor parcial de degradación química que se utiliza en el diseño del estado límite de estabili-dad interna en los muros TEM. Este estudio presenta los resultados de los análisis realizados mediante simulaciones numéricas para estimar, en primer lugar, los cambios de temperatura y humedad relativa en el suelo para diferentes propiedades del terreno y condiciones atmosféricas de contorno, y, en segundo lugar, los cambios temporales de resistencia y rigidez en correas de PET enterradas simuladas y colocadas en diferentes entornos de suelo mientras se someten a diferentes cargas de tracción y temperaturas.Postprint (published version

Modélisation de l'effet de la température et de l'humidité relative du sol sur les performances des produits de renforcement des sols à base de sangles en PET

Polyester (PET) strap reinforcement materials are now used routinely as soil reinforcement for mechanically stabilized earth (MSE) walls. The important role of temperature and relative humidity on the chemical degradation of PET fibres due to hydrolysis is well documented in the literature. Strength and stiffness of the polyester fibres can be expected to decrease with increasing temperature and in the presence of moisture. This has practical implications for the selection of the partial factor for chemical degradation that is used in internal stability limit state design in MSE walls. The PET multi-filament core of the straps is protected against installation damage and moisture by a polyethylene sheath. This study presents the results of analyses using numerical simulations that were carried out to estimate, first, the in-soil temperature and relative humidity changes for different ground properties and atmospheric boundary conditions, and second, the temporal strength and stiffness changes in simulated buried PET straps placed in different soil environments while subjected to different tensile loads and temperatures. The soil properties in the analyses are moisture content, hydraulic conductivity (i.e., soil moisture retention curve), soil porosity and intrinsic permeability.Postprint (published version

Comparison of geosynthetic reinforced soil wall solutions using analytical design methods and numerical modelling

European design standard (prEN-1997 202x) permits the use of suitably verified numerical models for the design of reinforced soil walls (RSW). The paper first compares three analytical design method outcomes (Coherent Gravity, Simplified, and Stiffness method) available in US (AASHTO 2020) and Canadian (CSA 2019) design codes. Polyester (PET) strap reinforcement arrangements from each method were then simulated using a 2D finite element model (FEM) which considered construction stages and transient compaction conditions. The models for each arrangement were analyzed using different material factors applied to the soil frictional strength. Serviceability limit states (SLS) and ultimate limit states (ULS) were evaluating via horizontal wall deformations, soil shear strains, and maximum reinforcement tensile loads. Numerical results remained within SLS and ULS criteria. The maximum tensile loads from the numerical models were close to, but lower than the predicted loads using the Stiffness Method, which in turn were lower than the loads predicted using the Simplified and Coherent Gravity methods.Peer ReviewedPostprint (published version

Coupled modelling of environmental in-soil conditions and their effects over polyester straps reinforced soil structures

Polyester (PET) strap reinforcement materials are being routinely used as soil reinforcement for mechanically stabilized earth (MSE) walls. Strength and stiffness of the polyester fibres can be expected to decrease with increasing temperature and in the presence of moisture. By using numerical simulations, mean in-soil temperature values could be approximated to the mean atmospheric yearly value with diminishing fluctuation with increased depth. In-depth relative humidity values were found to present a constant behaviour for three of the four imposed boundary condition. Temporal variations in the response of PET straps were adequately modelled with viscous models within different soil environments.Postprint (published version

Strength reduction analysis in polymeric reinforced soil walls

The latest revision of EN-1997 allows for the use of numerical tools to design geotechnical structures, provided limit state conditions are thoroughly evaluated were analysis of the construction and post-construction stages must be included. Regarding ultimate limit state conditions, material factors must be used as to evaluate the effect of soil strength reduction on the performance of the structure. The present study focuses on the design of an idealized 10.5 m-tall reinforced soil wall with discrete concrete facing panels and polymeric strip reinforcements using finite element tools. A manual strength reduction analysis was performed, which showed no sign of structural failure, but rather hints of probable failure mechanisms which may occur, provided the structure is subjected to further unfavorable conditions.Postprint (published version

Modelling the effect of in-soil temperature and relative humidity on performance of PET strap soil reinforcement products

Polyester (PET) strap reinforcement materials are now used routinely as soil reinforcement for mechanically stabilized earth (MSE) walls. Strength and stiffness of the polyester fibres can be expected to decrease with increasing temperature and in the presence of moisture. This study presents the results of analyses using numerical simulations that were carried out to estimate, first, the in-soil temperature and relative humidity changes for different ground properties and atmospheric boundary conditions, and second, the temporal strength and stiffness changes in simulated buried PET straps placed in different soil environments while subjected to different tensile loads and temperatures.Postprint (published version