International audienceThis paper is a contribution to the characterization of permeability to gas... more International audienceThis paper is a contribution to the characterization of permeability to gas of unsaturated GCLs, with applications in cover liners of municipal solid waste landfills. Conducting such tests at low gas pressure gradient limits the risk of moisture distribution change in the bentonite, which has been observed under high pressure gradients. However, a consequence of a low pressure gradient is a small gas flow rate that is difficult to measure with good accuracy. Therefore, a solution may be the use of transient state tests, like the falling pressure test adapted to GCLs permeability characterization. This paper shows the influence of the main parameters related to the test and to the material tested (natural or activated calcium bentonite, moisture content, presence or not of small cracks in the bentonite). The results obtained showed good repeatability for gas differential pressures up to 40 kPa for the test conditions employed in this work. The results showed tha...
Slopes and Retaining Structures Under Seismic and Static Conditions, 2005
This paper presents the results of a study on the use of geosynthetic reinforced embankments for ... more This paper presents the results of a study on the use of geosynthetic reinforced embankments for the protection of buried pressurised pipes by means of laboratory tests. The expansion of a pipe inside reinforced and unreinforced sand was simulated in models studies in the laboratory using a large rigid steel tank. Different types and configurations of geosynthetics were tested including woven geotextiles, geogrids and metallic reinforcements. The scale of the models in the laboratory was 1:5 and the series of the tests involved a continuous expansion of the pipe walls (thin rubber membrane) until failure of the soil mass was achieved. The results obtained showed a significant influence of the presence of the reinforcement on the pressure in the pipe, depending on reinforcement type and arrangement, and the potential use of reinforced embankments to protect pressurized pipes.
... Bearing force mobilisation in pull-out tests on geogrids. Ennio Marques Palmeira Correspondin... more ... Bearing force mobilisation in pull-out tests on geogrids. Ennio Marques Palmeira Corresponding Author Contact Information , E-mail The Corresponding Author. Department of Civil and Environmental Engineering-FT, University of Brasilia, 70910-900, Brasilia, DF, Brazil. ...
... Fannin, RJ (1986). Geogrid reinforcement of granular layers on soft clay -- a study at model ... more ... Fannin, RJ (1986). Geogrid reinforcement of granular layers on soft clay -- a study at model and full scale, D.Phil thesis, University of Oxford. Giroud, JP & Noiray, L. (1981). ... Love, JP (1984). Model testing of geogrids in unpaved roads. DPhil thesis, University of Oxford. ...
ABSTRACT Nonwoven geotextiles have been commonly used in filtration and drainage of geotechnical ... more ABSTRACT Nonwoven geotextiles have been commonly used in filtration and drainage of geotechnical engineering works. This paper presents a study on the use of such materials in drainage and filtration systems of tailings dams. Different combinations of tailings and geotextiles were submitted to gradient ratio (GR) tests under confinement in the laboratory with varying values of stress levels and hydraulic gradients. The results of GR tests under confining stresses up to 2000kPa are presented and discussed. The dimensions of the tailings particles entrapped in the geotextile specimens and those that piped through the geotextile were also assessed. Geotextile specimens from the drainage system of a tailings dam were exhumed for analyses, as part of the research programme. The results obtained showed that stress levels and the hydraulic gradients used in the tests influenced the behaviour of the system. Physical and microscopic analyses of the specimens tested showed greater geotextile impregnation by tailings particles in the field than in the laboratory. The overall performance of the geotextiles tested under laboratory conditions was satisfactory. However, in the field segregation of tailings particles and transport of fines in suspension can subject the filter to more complex and severe clogging mechanisms, not properly simulated in current standard testing procedures.
ABSTRACT This paper presents the results of gradient ratio tests on different soil - geotextile s... more ABSTRACT This paper presents the results of gradient ratio tests on different soil - geotextile systems under normal stresses up to 2000 kPa. Different types of soil and geotextiles were tested, and the soil particles that passed through the geotextile and those retained in it were collected for particle size analyses. The results obtained show that the use of definitions of gradient ratio based on the measurement of water heads close to the geotextile layer can be useful for a better identification of geotextile-clogging mechanisms. The entrapment of soil particles in the geotextile increases its retaining capacity and alters the conditions for further clogging. The dimensions of the entrapped soil particles can be greater than the geotextile pore dimensions under unconfined conditions and are controlled by soil and geotextile characteristics and by the soil sample preparation technique employed. The results suggest that current retention and permeability criteria for geotextile filters can be excessively conservative. Discussions on geotextile performance in the test and under field conditions are also presented as well as limitations and new proposals for the interpretation of the gradient ratio test.
The behaviour of soilgeotextile systems in filtration tests is reported for nonwoven geotextiles... more The behaviour of soilgeotextile systems in filtration tests is reported for nonwoven geotextiles under unidirectional flow. A new apparatus was developed to preform filtration tests under an applied vertical stress, and tests were then conducted with different soils and nonwoven geotextiles in order to evaluate the clogging potential and retention capacity of these materials under rather severe combinations of geotextile and soil characteristics. Results show that the geotextiles perfomed well and that observed permeability losses were acceptable even for gradient ratios close to 3. No progressive piping was observed, and it is believed that the retention capacity of the geotextiles may be influenced by their manufacturing process. In general, theoretical predictions for the maximum particle size passing through the geotextile compared well with measurements. Key words: geotextiles, filtration, gradient ratio, permeability, soil retention, clogging.
International audienceThis paper is a contribution to the characterization of permeability to gas... more International audienceThis paper is a contribution to the characterization of permeability to gas of unsaturated GCLs, with applications in cover liners of municipal solid waste landfills. Conducting such tests at low gas pressure gradient limits the risk of moisture distribution change in the bentonite, which has been observed under high pressure gradients. However, a consequence of a low pressure gradient is a small gas flow rate that is difficult to measure with good accuracy. Therefore, a solution may be the use of transient state tests, like the falling pressure test adapted to GCLs permeability characterization. This paper shows the influence of the main parameters related to the test and to the material tested (natural or activated calcium bentonite, moisture content, presence or not of small cracks in the bentonite). The results obtained showed good repeatability for gas differential pressures up to 40 kPa for the test conditions employed in this work. The results showed tha...
Slopes and Retaining Structures Under Seismic and Static Conditions, 2005
This paper presents the results of a study on the use of geosynthetic reinforced embankments for ... more This paper presents the results of a study on the use of geosynthetic reinforced embankments for the protection of buried pressurised pipes by means of laboratory tests. The expansion of a pipe inside reinforced and unreinforced sand was simulated in models studies in the laboratory using a large rigid steel tank. Different types and configurations of geosynthetics were tested including woven geotextiles, geogrids and metallic reinforcements. The scale of the models in the laboratory was 1:5 and the series of the tests involved a continuous expansion of the pipe walls (thin rubber membrane) until failure of the soil mass was achieved. The results obtained showed a significant influence of the presence of the reinforcement on the pressure in the pipe, depending on reinforcement type and arrangement, and the potential use of reinforced embankments to protect pressurized pipes.
... Bearing force mobilisation in pull-out tests on geogrids. Ennio Marques Palmeira Correspondin... more ... Bearing force mobilisation in pull-out tests on geogrids. Ennio Marques Palmeira Corresponding Author Contact Information , E-mail The Corresponding Author. Department of Civil and Environmental Engineering-FT, University of Brasilia, 70910-900, Brasilia, DF, Brazil. ...
... Fannin, RJ (1986). Geogrid reinforcement of granular layers on soft clay -- a study at model ... more ... Fannin, RJ (1986). Geogrid reinforcement of granular layers on soft clay -- a study at model and full scale, D.Phil thesis, University of Oxford. Giroud, JP & Noiray, L. (1981). ... Love, JP (1984). Model testing of geogrids in unpaved roads. DPhil thesis, University of Oxford. ...
ABSTRACT Nonwoven geotextiles have been commonly used in filtration and drainage of geotechnical ... more ABSTRACT Nonwoven geotextiles have been commonly used in filtration and drainage of geotechnical engineering works. This paper presents a study on the use of such materials in drainage and filtration systems of tailings dams. Different combinations of tailings and geotextiles were submitted to gradient ratio (GR) tests under confinement in the laboratory with varying values of stress levels and hydraulic gradients. The results of GR tests under confining stresses up to 2000kPa are presented and discussed. The dimensions of the tailings particles entrapped in the geotextile specimens and those that piped through the geotextile were also assessed. Geotextile specimens from the drainage system of a tailings dam were exhumed for analyses, as part of the research programme. The results obtained showed that stress levels and the hydraulic gradients used in the tests influenced the behaviour of the system. Physical and microscopic analyses of the specimens tested showed greater geotextile impregnation by tailings particles in the field than in the laboratory. The overall performance of the geotextiles tested under laboratory conditions was satisfactory. However, in the field segregation of tailings particles and transport of fines in suspension can subject the filter to more complex and severe clogging mechanisms, not properly simulated in current standard testing procedures.
ABSTRACT This paper presents the results of gradient ratio tests on different soil - geotextile s... more ABSTRACT This paper presents the results of gradient ratio tests on different soil - geotextile systems under normal stresses up to 2000 kPa. Different types of soil and geotextiles were tested, and the soil particles that passed through the geotextile and those retained in it were collected for particle size analyses. The results obtained show that the use of definitions of gradient ratio based on the measurement of water heads close to the geotextile layer can be useful for a better identification of geotextile-clogging mechanisms. The entrapment of soil particles in the geotextile increases its retaining capacity and alters the conditions for further clogging. The dimensions of the entrapped soil particles can be greater than the geotextile pore dimensions under unconfined conditions and are controlled by soil and geotextile characteristics and by the soil sample preparation technique employed. The results suggest that current retention and permeability criteria for geotextile filters can be excessively conservative. Discussions on geotextile performance in the test and under field conditions are also presented as well as limitations and new proposals for the interpretation of the gradient ratio test.
The behaviour of soilgeotextile systems in filtration tests is reported for nonwoven geotextiles... more The behaviour of soilgeotextile systems in filtration tests is reported for nonwoven geotextiles under unidirectional flow. A new apparatus was developed to preform filtration tests under an applied vertical stress, and tests were then conducted with different soils and nonwoven geotextiles in order to evaluate the clogging potential and retention capacity of these materials under rather severe combinations of geotextile and soil characteristics. Results show that the geotextiles perfomed well and that observed permeability losses were acceptable even for gradient ratios close to 3. No progressive piping was observed, and it is believed that the retention capacity of the geotextiles may be influenced by their manufacturing process. In general, theoretical predictions for the maximum particle size passing through the geotextile compared well with measurements. Key words: geotextiles, filtration, gradient ratio, permeability, soil retention, clogging.
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