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Botelho K.J.,Geosyntec Consultants | Heynes O.,Insight Numerics LLC | Giroud J.-P.,JP GIROUD Inc.
Geotechnical Special Publication | Year: 2014

The accurate calculation of wind uplift forces on an exposed geomembrane is essential for generating design requirements for the anchorage system. These requirements often largely dictate construction costs, so inaccuracies in the uplift calculation may have significant economic repercussions. Inaccuracies may occur when using generic suction factors rather than a site-specific assessment using computational fluid dynamics (CFD) technology. This paper presents preliminary research conducted to determine whether potential cost savings warrant more complex CFD modeling. Preliminary results comparing a two-dimensional case of an exposed geomembrane (which was used to develop generic suction factors commonly used to evaluate wind uplift) indicate the wind uplift forces calculated from a CFD model resulted in tensions that were significantly less than those using generic suction factors. Preliminary research was performed with the intention of employing CFD modeling to refine the simple prescription of generic suction factors on a site-specific basis. © 2014 American Society of Civil Engineers. Source

Cazzuffi D.,Centro Elettrotecnico Sperimentale Italiano | Giroud J.P.,JP GIROUD Inc. | Scuero A.,Carpi Technology | Vaschetti G.,Carpi Technology
9th International Conference on Geosynthetics - Geosynthetics: Advanced Solutions for a Challenging World, ICG 2010 | Year: 2010

In more than 270 dams worldwide, geomembranes are the main waterproofing component. The geomembrane is generally associated with other geosynthetics performing various functions, thereby forming a geosynthetic barrier. In this paper, uses of geosynthetic barriers in the various types of dams are reviewed. The types of dams reviewed include: embankment dams (earthfill and rockfill dams), concrete and masonry dams, and roller compacted concrete (RCC) dams. Design and construction aspects are considered, as well as selection of geosynthetic materials and performance (including seepage control and durability). The paper is illustrated using a number of examples of new dams and rehabilitation of existing dams, including examples of the early dams constructed or rehabilitated using geosynthetic barriers in the 1950s, 1960s and 1970s. Source

Giroud J.P.,JP GIROUD Inc.
9th International Conference on Geosynthetics - Geosynthetics: Advanced Solutions for a Challenging World, ICG 2010 | Year: 2010

A rational development of criteria for geotextile and granular filters is presented. It is shown that, whereas two criteria are sufficient for granular filters, a permeability criterion and a retention criterion, four criteria are required for geotextile filters. The four criteria are: permeability criterion, retention criterion, porosity criterion and thickness criterion. The analysis shows that the permeability criterion includes two requirements, a pore water pressure requirement and a flow rate requirement. It is shown that, in the case of granular filters, the two requirements generally reduce themselves to the classical Terzaghi's permeability criterion, whereas, in the case of geotextile filters, the hydraulic gradient in the soil next to the filter determines which of the two requirements is the most stringent. Regarding the retention criterion, the analysis shows that, for both geotextile and granular filters, a complete retention criterion should take into account the density of the soil and the coefficient of uniformity of its particle size distribution curve. This analysis explains the limitations of the classical Terzaghi's retention criterion. The retention criterion proposed herein provides a means to overcome these limitations. Then, the need for two additional criteria for geotextile filters is pointed out. These two criteria are a porosity criterion expressed as a minimum porosity of the filter and a thickness criterion expressed as a minimum thickness of the filter. It is shown that these two criteria are always met by granular filters and, therefore, are needed only for geotextile filters. Source

Giroud J.P.,JP GIROUD Inc. | Gourc J.P.,Grenoble University
10th International Conference on Geosynthetics, ICG 2014 | Year: 2014

The first double liner with two geomembranes was constructed in June 1974 and has been in continuous service since then. The lined structure is a 10 m deep, 195 m long and 55 m wide water reservoir, located on top of a 50 m high 33°slope. The geotechnical study concluded that the slope was stable, but could become unstable in case of major leakage of water from the reservoir. Any risk of instability was unacceptable because a large chemical plant was, and still is, located at the toe of the slope. Because safety was essential, a double liner was recommended by the senior author. The primary liner is a 1.5 mm thick butyl rubber geomembrane. The secondary liner is a bituminous geomembrane formed in situ by impregnating a geotextile with hot bitumen. The leakage detection layer between the two liners is made of gravel stabilized with mortar. The reservoir has been monitored by the plant personnel since the end of construction. No leakage was detected until 2004, i.e. 30 years after construction, when atnckle of water appeared at the monitoring building. The leak, a defective seam, was repaired under water. The reservoir described in this paper can be considered a historic landmark of the geosynthetic discipline. Source

Giroud J.P.,JP GIROUD Inc. | Gourc J.P.,Joseph Fourier University | Kavazanjian E.,Arizona State University
Geosynthetics International | Year: 2012

Hydraulic transmissivity tests on common geosynthetic and granular drainage materials (e.g. geonets and gravel) show that the hydraulic transmissivity of these materials often depends heavily on the hydraulic gradient, which indicates that the flow is non-laminar. Despite the non-laminar nature of flow in these materials, Darcy's equation and equations derived from Darcy's equation are extensively used for the design of geosynthetic and granular drainage systems, even though these equations are strictly valid only for laminar flow. Therefore it is important to identify the drainage materials and flow conditions for which the flow is laminar in order to evaluate the applicability of Darcy's equation. In classical hydrodynamics, the conditions for laminar flow are generally described in terms of a limiting Reynolds number. This paper provides guidance for Reynolds number calculation in geosynthetic and granular drains, and presents a methodology to establish the conditions for laminar flow as a function of the Reynolds number. Numerical applications of the methodology show that, for typical hydraulic gradients used in hydraulic transmissivity tests in the laboratory and encountered in drainage layers in the field, flow is generally laminar in needle-punched nonwoven geotextiles and sand, whereas it is generally non- laminar in geonets and gravel. However, in the case of geonets adjacent to geotextiles (such as in geocomposites), the flow becomes closer to laminar conditions as the geotextile progressively intrudes into the geonet channels under increasing values of the applied normal stresses. Practical recommendations are given for the use of Darcy's equation and equations derived from Darcy's equation to obtain approximate solutions when flow is not laminar. ©2012 Thomas Telford Ltd. Source

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