1,721,007 research outputs found
Soil-geogrids interaction mechanisms – role of the soil grains size and of the reinforcements bearing members
No full textIn this work the role of the soil grains size and of the bearing members of the geogrids on the soil geogrid interaction mechanisms is shown. First, a theoretical discussion of how these factors affect the resistance of the studied interfaces is presented, including different proposals for its evaluation. Pullout tests were carried out in a large box, following the guidelines of the European standard in preparation. The results of sixteen tests (that correspond to 48 samples tested) with two distinct soils and four different geogrids are presented. Virgin samples and samples without bearing members were tested. A comparison between the experimental and the theoretical results is done and the main conclusions of the study are put forward<br/
Effect on the mechanical behaviour of geosynthetics of the installation damage – initial results
No full textIn this work the effect of the installation procedures of geosynthetics on their mechanical behaviour is shown. First, a description of how the damage during installation can occur is presented, including the procedures that can be used to minimise the consequences of the damage due to the installation of geosynthetics in real construction sites. The test program, still going on, is presented and includes two different procedures of inducing the damage in geosynthetic samples: laboratory simulations and installation of the geosynthetics in temporary embankments. The initial results of the test program referring to the undamaged samples and to the damaged samples using the laboratory simulation are presented: tensile tests results regarding all the geosynthetics tested and creep rupture test results of two geosynthetics. The evaluation of the effect of the installation damage on the long term behaviour of geosynthetics obtained from the experimental study and using the standard approach is compared. The main conclusions of this work are also presented
Soil-geosynthetic interaction - influence of soil particles size and geosynthetic structure
No full textThis paper reports the results of pullout tests on five different geosynthetics embedded in two different granular soils. Soil and geosynthetic properties are described and soil-geosynthetic interaction behaviour is studied. Based on the results of pullout tests, the influence of soil particle size, geosynthetic structure, and the role of geogrid bearing members are discussed. The main conclusion is that the influence of soil particle size on soil-geosynthetic interaction is important, but its significance depends on several factors. With geogrids, the relative sizes of soil particles and geogrid apertures, and the thickness of the geogrid bearing members, determine soil-geogrid interface shear resistance. A marked increase in soil-geogrid interface shear resistance was observed when the soil contained a significant percentage of particles with sizes slightly greater than the thickness of the geogrid bearing members, but smaller than the geogrid apertures. Tests, on geogrids in which the bearing members had been cut, show a significant decrease in soil-geogrid interface shear resistance. The influence of soil particle size is less important for geotextiles and geocomposites. Although the structure of geotextiles and geocomposites has an effect on soil-reinforcement interface behaviour, mobilised pullout resistance is also affected by the axial tensile stiffness of geotextiles and geocomposite
Hydraulic properties of a geosynthetic composite after mechanical damage and abrasion and their variability
No full textIn this paper results of tests to assess the effect of mechanical damage (generally associated with installation processes) and abrasion are presented. Laboratory tests were carried out. The material tested is a composite consisting of two overlapped geosynthetics: a nonwoven geotextile and a woven geogrid. The composite was submitted to each referred agent (mechanical damage and abrasion) in isolation and sequentially, in order to assess an eventual synergetic effect. The effect of the damage induced in some physical and hydraulic properties of geosynthetics was assessed: characteristic opening size and permittivity. The variability of these properties was assessed by using either 1 or 3 tests per sample. The results indicate that the number of tests carried out leads to different conclusions, pointing out the need of adjusting the number of specimens to be tested. The mechanical damage seems to result in a significant clogging of the geocomposite’s pores, while the abrasion damage resulted in decreased constrictions to the flow of water. Some synergisms were observed for mechanical and abrasion damage
Synergisms between laboratory mechanical and abrasion damage on mechanical and hydraulic properties of geosynthetics
Full text linkThis paper analyses the existence of synergisms between some endurance durability agents of geosynthetics – mechanical damage (usually associated with installation) and abrasion damage (often associated with cyclic actions, for example due to contact with ballast). Three geosynthetics (geotextile, geogrid and geocomposite) were submitted to mechanical damage and abrasion damage using index laboratory tests. The geosynthetics were exposed first individually to each agent (single exposure) and then sequentially to the two agents (multiple exposures). To ensure the results were statistical representative, each set of tests was performed three times. The consequences of the damage induced were visible (naked eye). Abrasion damage was found the most critical damage mechanism for the tensile properties, particularly for the geogrid and geocomposite tested. The connections between their components created potential fragility points in the abrasion test. Due to its structure, combined with high mass per unit area and thickness, the geotextile tested survived well the damage induced. A positive synergy between the mechanical and the abrasion damage induced was found for the tensile properties of the geosynthetics most affected by damage, more important for their tensile strength than for their secant stiffness. The mechanical damage was the most critical mechanism for the permittivity of the geotextile and the geocomposite, likely due to clogging of their pores. For the permittivity and the characteristic opening size of these geosynthetics, negative synergy between mechanical and abrasion damage was found; the traditional approach was found likely to result in unsafe estimates of these properties
An equipment to perform damage during installation tests of geosynthetics
No full textThe equipment developed to carry out damage during installation tests in laboratory on geosynthetics is described. These tests allow inducing in laboratory the effects of the procedures of installation on site on the geosynthetics. The test equipment and test procedures are described and the characteristics of the granular material and the geosynthetic used in this study are referred. After carrying out the damage during installation laboratory tests, intact and damaged samples of geosynthetic were: 1) observed using scanning electronic microscope; and 2) carried out tensile tests in order to characterise the damaged induced
Synergy between mechanical damage and abrasion of a composite geosynthetic and its variability
No full textIn this paper results of tests to assess the effect of mechanical damage (generally associated with installation processes) and abrasion are presented. Laboratory tests were carried out. The material tested is a composite consisting of two overlapped geosynthetics: a nonwoven geotextile and a woven geogrid. The composite was submitted to each referred agent (mechanical damage and abrasion damage) in isolation and sequentially, in order to assess an eventual synergetic effect. The effect of the damage induced in the short-term mechanical properties of the geosynthetic was assessed. The variability of these properties was assessed by using either 1 or 3 tests per sample. Abrasion damage (either isolated or combined with mechanical damage) was the most critical mechanism, leading to higher reductions of tensile strength. Increasing the number of tests used to characterise the samples from 1 to 3, has reduced the variability of the properties assessed, although the tensile strength values decreased and the peak strain and secant stiffness modulus for 2% strain increased. The number of characterisation tests carried out per sample didn’t affect the trends observed associated with the damage induced. Some synergisms were observed for mechanical and abrasion damag
Bearing ratio of a fine soil reinforced with geosynthetics: influence of the reinforcement type and the soil water content
No full textThis paper reports an investigation on the effects of reinforcing a fine soil with three different geosynthetic solutions and their behaviour under loading. The effectiveness of the reinforcement was investigated through California Bearing Ratio, CBR, tests. The reinforcement solutions tested were: geogrid (GGR), geocomposite (GCR), association of geogrid and geotextile (GGR + GTX). The response of the unreinforced fine soil was compared to those of the same soil with one layer of reinforcement. The influence of the initial water content of the soil on the bearing capacity was analysed using five different values (11.9%; 13.9% (optimum); 15%; 17% and 19%). Including a layer of reinforcement improved the bearing capacity ratio and the stiffness of the samples. The best improvement in bearing capacity was found for GGR, followed by GGR + GTX and then GCR, and can be explained by the differences in stiffness and structure of the reinforcements. The mobilisation of the reinforcement depended on the type of reinforcement, the initial water content of the sample and the penetration induced to the sample. The soil initial water content affected the response significantly. Higher initial water contents lead to lower CBR values, for both unreinforced and reinforced samples. However, the effectiveness of each reinforcement varied with the initial water content; for GGR and GGR + GTX an initial water content of 17% lead to the higher bearing capacity ratio, while for GCR this occurred for the lowest value of the initial water content considered (11.9%)
Geosynthetics standardization
No full textThis paper pretends to inform the geotechnical community of some aspects of the standardization of geosynthetics at European and National level. During the last years great advances were achieved in the standardization of the geosynthetics. Due to different difficulties, those who work with these materials, namely owners, designers, contractors and inspectors, did not acknowledge these advances. This work pretends to fulfil this deficit, allowing for the update on this area and consequently for a better quality on the technical works involving geosynthetics
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