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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.
- 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.
- 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.