Geosynthetic capillary barriers: current state of knowledge
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ABSTRACT: This paper provides theoretical background, laboratory data and full-scale measurements useful in understanding the interaction between soils and geosynthetics under unsaturated conditions. It also includes an evaluation of the current state of knowledge regarding the hydraulic properties of porous geosynthetics under unsaturated conditions relevant for geosynthetic capillary barrier design. These properties include the water retention curve and the hydraulic conductivity function. In addition, the mechanisms involved in the development of capillary barriers are evaluated to explain the storage of water at the interface between materials with contrasting hydraulic conductivity (e.g. a fine-grained soil and a nonwoven geotextile). Finally, specific applications are presented to illustrate new opportunities and applications that may result from a better understanding of the unsaturated hydraulic properties of geosynthetics. Experimental data are provided illustrating that geosynthetic capillary barriers are superior to soil-only capillary barriers. Based on this observation, it is emphasized that no capillary barrier should be designed without consideration of the enhanced performance offered by the inclusion of nonwoven geotextiles under the fine-grained soil component of the cover.Keywords:
Geosynthetics
Geotextile
Clogging
Drainage through pipes plays an important role in tailings pond projects. Reductions in drainage capacity and even clogging of drainage pipes are common issues, especially in tailings projects. To address these clogging issues, a drainage pipe with a replaceable porous-foam filter core (referred to as DPRF) is proposed. This paper studied the drainage characteristics of DPRF wrapped with a woven geotextile and traditional drainage pipes wrapped with a nonwoven geotextile (referred to as DPNG) in fine tailings sands with a reduced scale model test. The results showed that the woven and nonwoven geotextiles could successfully retain fine tailings sand; however, the woven geotextile easily clogged as the experiment progressed. For the DPRF wrapped with a woven geotextile, the larger the aperture of the woven geotextile, the higher the drainage rate of the pipe. The average drainage rate of the DPNG was larger than that of the DPRF wrapped with the woven geotextile. It can thus be inferred that the DPRF wrapped with the woven geotextile is not a good solution to prevent physical clogging. Alternatively, it is suggested that the DPRF wrapped with the nonwoven geotextile can be used to alleviate chemical clogging problems.
Geotextile
Clogging
Geosynthetics
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Nonwoven geotextiles have been used for drainage and filtration in geotechnical engineering works for many years. Concerns related to drainage capacity and clogging potential still remain as factors that restrain a broader use of geotextiles for drainage systems, particularly in major engineering projects. This paper presents the test results of the hydraulic characteristics of partially clogged geotextiles under pressure. Partial clogging can occur during spreading and compaction of soil on geotextiles or throughout the service life of the drainage system. Geotextile specimens, artificially clogged in the laboratory and exhumed from actual field works, were tested to assess their normal and longitudinal permeabilities under different levels of soil impregnation and normal stresses. The results obtained showed that partial clogging significantly influenced the mechanical and hydraulic characteristics of nonwoven geotextiles and that soil impregnation was not necessarily detrimental to the geotextile longitudinal permeability under stress. Comparisons of test and predicted results, confirmed that the expression reported by Giroud in 1996 is a useful tool for the prediction of nonwoven geotextile permeabilities under virgin and soil impregnated conditions. Data on the impregnation levels of geotextile specimens exhumed from actual field works are also presented and discussed.
Clogging
Geotextile
Geosynthetics
Geomembrane
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Citations (81)
Nonwoven geotextiles have been used as filters for over four decades in geotechnical and geoenvironmental works. These products have a complex fibre matrix and their behaviour as filters depends on how this matrix interacts with fluids and soil particles. Therefore, uncertainties still exist regarding prediction of geotextile filter performance under severe and critical situations. This paper investigates how confinement and partial clogging influence the dimensions of openings in nonwoven geotextiles. Bubble point (BBP) tests were carried out on six nonwoven geotextiles under unconfined and confined (equivalent vertical stresses of up to 1000 kPa) conditions with and without partial clogging of the geotextile. The results obtained show significant influences of confinement and partial clogging on geotextile opening dimensions and retention capacity. The results of O 95 from bubble point tests on unconfined and virgin specimens compared well with results from hydrodynamic tests. Comparisons between BBP results and data from filtration tests under confinement are also presented and discussed. The repercussions of reductions in opening size caused by confinement and partial clogging on geotextile clogging potential and filter criteria are discussed.
Clogging
Geotextile
Geosynthetics
Filtration (mathematics)
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Citations (52)