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- Long-term response and design of two geosynthetics: effect of field installation damagePublication . Pinho-Lopes, Margarida; Paula, António Miguel; Lopes, Maria de LurdesThis paper contributes to understanding how installation damage of geosynthetics influences their long-term response and design. A geotextile and a geogrid were exhumed after installation under real conditions; their long-term tensile behaviour was investigated using conventional creep and creep rupture tests. Reduction factors for installation damage, creep and their combined effect were computed. The main aim of the paper was to assess how the long-term response of the geosynthetics was influenced by installation damage and whether it would be necessary to update current design approaches. The installation damage affected the mechanical response of both geosynthetics; important strength reductions were observed, particularly for the most severe installation conditions. The results indicate that, contrary to what has been reported in the literature, the creep rupture response of the geotextile changed after installation damage. When tested under similar creep loads (fraction of the sample tensile strength), both geosynthetics exhibited reduced potential for creep rupture and smaller strains at the end of primary creep. Changes in stiffness were less important than those for strength, for both short- and long-term response. There was synergy between installation damage and creep; the traditional approach to design was unsafe for the geotextile and slightly conservative for the geogrid.
- Combined effect of damage during installation and long-term mechanical behavior of geosyntheticsPublication . Paula, António Miguel; Pinho-Lopes, Margarida; Lopes, Maria de LurdesOne of the main questions in using geosynthetics in civil works or ground applications is their durability, in particular, the mechanical actions to which they are subject during the installation processes and construction. Under these actions the geosynthetics can be damaged and the changes in their properties can compromise the performance of the constructions where these materials are used. To contribute to the comprehension on the effect of damage during installation on long-term mechanical behaviour of geosynthetics, a research program was established. Two different geosynthetics have been studied: a woven PP-tape and a woven PE geogrid. These materials have been subjected to field damage tests, using two different soils and two compaction energies. To characterise the effect of the damage induced in the long-term mechanical behaviour, tensile creep tests and creep rupture tests were carried out, according with the procedures described in EN ISO 13431. The results obtained are compared and discussed. The main conclusions of the study are presented.
- Hyperbolic models to represent the effect of mechanical damage and abrasion on the short-term tensile response of a geocompositePublication . Lombardi, G.; Pinho-Lopes, Margarida; Paula, António Miguel; Bastos, AntónioThe objective of this study was to analyse the short-term tensile response of a geocomposite (a geotextile and a geogrid overlapped) and apply hyperbolic models to describe its load-strain tensile curves. Data from specimens submitted to mechanical damage, abrasion, and mechanical damaged followed by abrasion were analysed. Reduction factors were proposed by comparing data from damaged specimens with those from undamaged specimens. The experimental results were compared with those fitted by the constitutive models to validate the model. The constitutive models demonstrated good fitting capacity. For any mechanical condition, the model parameters could be estimated by relating the experimental tensile properties of the geocomposite with adjustment coefficients, which allowed for describing the tensile load-strain curves with good accuracy. The reduction factors for the specimens subjected to mechanical damage followed by abrasion were lower than the values which would be obtained if the damages were considered individually.
- 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.
- Constitutive models for numerical analysis of the short- and long-term behavior of geosynthetics and mechanical damagePublication . Lombardi, G.; Paula, António Miguel; Lopes, Margarida PinhoAnalyse the tensile response of different geosynthetics; Apply constitutive models to describe the nonlinear tensile behaviour of these materials in the short- and the long-term, before and after damage; Propose model parameters for intact and damaged specimens.
- Pullout response of geogrids after installationPublication . Pinho-Lopes, Margarida; Paula, António Miguel; Lopes, Maria de LurdesDamage of geosynthetics during installation processes can affect their performance, so they are typically represented in design by applying reduction factors to their tensile strength measured in the laboratory. This paper contributes to better understanding whether this is representative of the pullout response of geogrids when confined in soil. The effects of installation damage induced in field trials of two extruded geogrids and one composite with a grid structure were studied. Pullout tests were used to characterise the impact of installation damage on the soil–geosynthetic interface interaction. The coefficients of interaction were analysed to assess the impact of different parameters, including the nominal strength of the geogrids and compaction energy applied. The coefficient of interaction was affected differently by installation, depending on both the geosynthetic and the soil in contact with it. Confinement in a soil with higher friction angle was more effective in mobilising the interface strength, for both undamaged and damaged samples. The type of soil in contact with the geosynthetics was more relevant for the interface strength than the normal stresses applied in the tests. The main lesson learned from this study is that the use of results from tensile strength of damaged materials to estimate the corresponding effects on their pullout response can lead to very conservative solutions.
- Geosynthetics for sustainable cities: 3D models and mechanical damagePublication . Paiva, Lucas; Lopes, Margarida Pinho; Valente, R.; Paula, António MiguelGeosynthetics for sustainable cities: 3D models and mechanical damage.
- 3D numerical modeling of geosynthetics for soil reinforcement: a bibliometric analysis and literature reviewPublication . Paiva, Lucas; Pinho-Lopes, Margarida; Paula, António Miguel; Valente, RoberttSoil reinforcement using geosynthetics is an efficient and cost-effective solution for a variety of geotechnical structures. Along with the increasing use of geosynthetics, there is a need to expand and enhance the design methodologies for these elements, which are still frequently based on conservative limit equilibrium approaches. In this paper, a bibliometric analysis was conducted on geosynthetic-reinforced soil structures (GRS), identifying the state of the art, research trends, and other indicators. The data were obtained from the Scopus platform and processed by VOSViewer v1.6 software. The initial search comprised 552 papers and the screening process selected 516 relevant papers from 1992 to October 2023. The study analyzed the occurrence of publications by year, keyword trends, authors, citations/co-citations, and bibliographic coupling. Then, a focus was given to 3D modeling research on geosynthetics, highlighting the dominant modeling techniques, material properties, and design challenges in GRS. The bibliometric analysis provided a crucial guideline in the identification of relevant papers and research trends, and a series of conclusions were presented regarding the 3D modeling techniques, choice of material properties, and boundary conditions.
- Damage during instalation laboratory test. Influence of the type of granular materialPublication . Paula, António Miguel; Pinho-Lopes, Margarida; Lopes, Maria de LurdesDamage during installation of geosynthetics has been subjected to extended studies, and became standardised with the introduction of ENV ISO 10722-1 in form of an index test for laboratory simulated installation damage. These tests should be carried out using a synthetic granular material, however, some authors have discussed the legitimacy of using such material. To contribute to the evaluation of the effect of the granular material used in laboratory damage tests, a research program was established. The test program consisted in performing damage during installation tests on the three geosynthetics using three different methods, over a minimum of five specimens per geosynthetic. To characterise the effect of the damage induced, tensile tests were carried out on both intact and damaged specimens. The three methods used for the DDI tests referred differ in the material used in contact with the geosynthetics: synthetic aggregate (ENV ISO 10722-1), granite aggregate and limestone aggregate. The results obtained after tensile tests (EN ISO 10319) are presented and discussed. The corresponding partial safety factors for damaged during installation of the geosynthetics studied are derived. The main conclusions of this study are presented.
- Soil–geosynthetic interaction in pullout and inclined-plane shear for two geosynthetics exhumed after installation damagePublication . Pinho-Lopes, Margarida; Paula, António Miguel; Lopes, Maria de LurdesThis paper contributes to a better understanding of how installation damage of geosynthetics can affect soil–geosynthetic interaction during pullout and inclined-plane shear. The effects of installation damage induced in field trials of a woven geotextile and a woven geogrid were studied. The results indicated that after installation the accumulation of a layer of fine particles over the geosynthetic can reduce the skin friction available, particularly for sheet materials. Installation damage can induce premature tensile failure in pullout tests, along the unconfined portion of the geosynthetic, causing a significant reduction in the corresponding coefficient of interaction. The contribution of the bearing members to the coefficient of interaction during pullout was estimated using equations from the literature. Such estimates were too optimistic. The installation damage induced had little influence on the soil–geosynthetic coefficient of interaction in the inclined plane shear test. The different relative movements of the soil and geosynthetic in pullout and inclined-plane shear, as well as the deformation of the reinforcements during pullout, enabled different mobilisation of the interface strength. For the comparable conditions tested, the coefficient of interaction from inclined plane shear tests was larger than that measured from pullout tests. The reduction factor for installation damage obtained from tensile tests overestimated the effects of the installation conditions on the soil–geosynthetic interface from both pullout and inclined plane shear tests.