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- Constitutive models for numerical analysis of the short- and long-term behavior of geosynthetics and mechanical damagePublication . Lombardi, G.; Paula, António Miguel; Lopes, Margarida Pinho; Pereira, A.B.Assess the tensile response of a geosynthetic in the short- and long-term Analyze damaged and undamaged specimens Fit tensile load vs. strain curves using constitutive models Estimate damaged tensile properties from model parameters of undamaged specimens. Extrapolate creep data Estimate long-term tensile properties from short-term model parameters
- Constitutive models for numerical analysis of the short- and long-term behavior of geosynthetics and mechanical damagePublication . Lombardi, Giovani; Lopes, Margarida Pinto; Paula, António Miguel; Pareira, António BastosThe objective of this research is to analyse the tensile response of geosynthetics, apply constitutive equations, and propose values for model parameters to represent the nonlinear behaviour of these materials in the short-term and the long-term. Data for specimens submitted to mechanical damage, abrasion damage, and mechanical damage followed by abrasion damage will be analysed. Nonlinear regressions of the experimental results will be performed to fit the load-strain curves to constitutive equations. For each geosynthetic, the results of damaged specimens will be statistically compared to those of the undamaged specimens to observe the influence of the induced damage on the tensile behaviour of the materials over time. Experimental results will be statistically compared with those obtained by the constitutive models to verify if the tensile properties and the model parameters are properly estimated.
- Simple constitutive models to study the influence of installation damage on the load-strain response of two geogridsPublication . Paula, António Miguel; Pinho-Lopes, MargaridaA key factor affecting the tensile response of geosynthetics is installation damage, repre-sented by a reduction factor capturing changes in tensile strength. Although often geosynthetics are repre-sented in numerical models by simple linear-elastic constitutive models and a stiffness, the response of geosynthetics to loading can be represented more realistically by non-linear constitutive models. Herein, simple constitutive models were used to represent the short-term tensile response of two geogrids (woven geogrid and uniaxial extruded geogrid). The tensile response of samples exhumed after field installation under real conditions was compared to that of the corresponding undamaged samples (as-received). The changes in response, particularly the change in tensile strength and stiffness, were presented and dis-cussed. The polynomial models (order 6) approximated the experimental data better than the hyperbolic models. Contrary to what has been reported in the literature, for the materials and test conditions present-ed herein and for the hyperbolic models, the parameter b cannot be estimated as the inverse of the materi-als tensile strength and the parameter is not a material constant. Both polynomial and hyperbolic mod-els approximated well the tangent stiffness for 2% strain obtained experimentally. The model parameters were normalised to the reduction factor for installation damage; for the hyperbolic models, the parameter b was practically unchanged after exhumation of the samples, while parameters a and showed no clear trend; the values of the stiffness normalised to the reduction factor for installation damage were not con-stant.
- Constitutive modelling of short-term tensile response of geotextile subjected to mechanical and abrasion damagesPublication . Paula, António Miguel; Pinho-Lopes, MargaridaThis paper discusses simple constitutive models to represent the tensile response of a geotextile (GTX) and the influence of two endurance durability factors on that response: mechanical and abrasion damage, acting independently and sequentially. The damage was induced in laboratory under standard conditions. Two types of models were used: polynomial and hyperbolic. The polynomial models (order 4 and 6) approximated the short-term tensile experimental data very well (and better than the hyperbolic model), but its model parameters have no physical meaning. The hyperbolic model parameters did not always have the physical meaning reported in the literature. Correction factors were introduced successfully, to achieve that physical meaning. These correction factors were not materials constants and were affected by the damage induced, and by the type of aggregate used in the mechanical damage tests. Equations to estimate the model parameters of the damaged samples were proposed using the model parameters for the undamaged sample and its properties (tensile strength and corresponding correction factor), and the reduction factors allowing for damage for the initial stiffness (Ji) and tensile strength (Tmax).
- Constitutive models and statistical analysis of the short-term tensile response of geosynthetics after damagePublication . Lombardi, Giovani; Paula, António Miguel; Pinho-Lopes, MargaridaThe objective of this research was to analyse the tensile response of three geosynthetics, to apply constitutive equations, and propose values for model parameters to represent the nonlinear behaviour of these materials in the short-term, supported by statistical analysis. Data for specimens of a nonwoven geotextile, a woven geogrid and a reinforcement geocomposite previously submitted to mechanical damage, abrasion damage, and mechanical damage followed by abrasion damage were analysed. Nonlinear regressions of the experimental results were performed to fit the load vs. strain curves to constitutive equations. For each geosynthetic, the results of damaged specimens were statistically compared to those of the undamaged ones to observe the influence of the induced damage on the tensile behaviour of the material. Experimental results were statistically compared with those obtained by the constitutive models to verify if the tensile properties and the model parameters were properly estimated. For the geotextile, significant changes in tensile properties were noticed only after sequential mechanical damage and abrasion damage. For the geogrid and the reinforcement geocomposite, abrasion damage was predominant due to considerable changes in the tensile properties and the shape of the load vs. strain curves. In general, the polynomial models fitted the ultimate tensile strength slightly better, while the hyperbolic-based models presented better approximation of the secant stiffness. For hyperbolic-based models, estimating curves for damaged materials from model parameters of undamaged specimens by applying adjustment coefficients and reduction factors allowing for damage was considered promising, with slight differences for average and median curves. Contrary to the literature, model parameter α was not a material constant, as it varied according to the material condition and the shape of the load vs. strain curve.
- Tensile behavior of weathered thermally bonded polypropylene geotextiles: analysis using constitutive modelsPublication . Carneiro, José Ricardo; Paula, António Miguel; Pinho-Lopes, MargaridaWeathering agents can significantly affect the mechanical response of geotextiles, particularly when long exposure periods are involved. Usually, in design, changes in the mechanical behavior of geotextiles are represented by reduction factors for their tensile strength. However, their full tensile force versus elongation response can be affected. The main aim of this work was to contribute to defining simple procedures to estimate tensile force versus elongation curves for weathered samples of geotextiles. The tensile response of two thermally bonded polypropylene geotextiles, before and after natural and artificial weathering, was assessed experimentally and analyzed using different constitutive models: polynomial (Orders 4 and 6) and hyperbolic. The influence of weathering on the mechanical response of the geotextiles was analyzed, polynomial and hyperbolic models for representing the tensile force versus elongation response were adopted and their parameters derived, and simple relations were implemented to estimate model parameters for weathered samples. Results revealed the occurrence of changes in the tensile behavior of the geotextiles, both under natural and artificial weathering conditions. Both groups of models fitted the experimental data properly. The Order 4 and 6 polynomial models are shown to have limited application, as the model parameters had no link to the tensile properties of the geotextiles. By contrast, the parameters of the hyperbolic model were linked to the tensile properties, particularly if affected by correction factors. The hyperbolic model parameters of the weathered samples were estimated using the model parameters of the reference samples and the reduction factors to allow for weathering (initial stiffness and tensile strength). These estimates proved to be adequate for representing the tensile response of weathered samples, particularly for low ranges of elongation. Finally, a simple procedure to represent the tensile response of weathered geotextiles was proposed. This procedure has shown promise in generating realistic tensile versus elongation curves.
- Constitutive models and statistical analysis of the short-term tensile response of geosynthetics after damagePublication . Lombardi, Giovani; Paula, António Miguel; Lopes, Margarida Pinho; Bastos, AntónioGeosynthetic is a generic name given to planar products, mostly composed of thermoplastic polymers, and used in contact with soil, rock or with any other material as part of a construction system [1]. Geosynthetics have several functions and may perform more than one simultaneously, such as soil reinforcement, stabilization of steep slopes, filtration, drainage, fluid barrier, erosion control and coastal protection [2]. The objective of this research was to analyse the short-term tensile response of three geosynthetics using the procedures described by [3], and to apply constitutive equations to represent the nonlinear behaviour of the materials. Data on specimens of a nonwoven polypropylene geotextile (GTX), a woven polyester geogrid (GGR) and a reinforcement polyester geocomposite (GCR) were analysed. Some specimens of each material were submitted to mechanical damage [4], abrasion [5], and mechanical damage followed by abrasion. Nonlinear regressions of the experimental data were performed to fit the load-strain curves to a hyperbolic-based equation depending on the tensile response of the geosynthetic: type A (GTX) or type B (GGR and GCR) [6]. For each geosynthetic, the results of damaged specimens were statistically compared to those of the undamaged specimens to observe the influence of the induced damage on the tensile behaviour of the material. Experimental data were statistically compared with those fitted by the constitutive models to verify if the tensile properties were properly estimated – namely the secant stiffness for 2% strain, the ultimate tensile strength, and the strain at maximum load. For the GTX, significant changes in tensile properties occurred only after mechanical damage followed by abrasion. For the GGR and the GCR, abrasion was the predominant damage due to considerable changes in the tensile properties and the shape of the load-strain curves. In general, the hyperbolic-based models presented good approximation of the empirical data. Curves for damaged materials were plotted using undamaged model parameters and applying adjustment coefficients and reduction factors allowing for damage, in which the goodness-of- fit was considered promising.
- A constitutive model for describing the tensile response of woven polyethylene terephthalate geogrids after damagePublication . Lombardi, Giovani; Pinho-Lopes, Margarida; Paula, António Miguel; Pereira, Antonio BastosA constitutive model was used to describe the tensile response of two woven Polyethylene Terephthalate (PET) geogrids, before and after mechanical damage. The model parameters of undamaged and damaged specimens were estimated via numerical regressions of test results. For each sample, the experimental and fitted tensile strengths were statistically compared using hypothesis tests. For each geogrid, tensile load-strain curves of damaged samples were drawn by applying scaling factors to the plot of the undamaged sample. The curve fittings resulted in high R-2 values for undamaged and damaged specimens of the geogrids. For most samples, there was no significant mean difference between the experimental and fitted tensile strength. The model allowed us to describe the load-strain curve of a geogrid from its tensile properties: & epsilon;(max), T-max and J(i). Regardless of the type of damage (in laboratory or in situ), the model was able to describe the load-strain curves of damaged samples using data from undamaged samples and scaling factors.