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Stephan Fourmont, David Beamier, Hajer Bannour

Environmental Design Considerations Using an Equivalency Index between Granular Drainage and Geosynthetic Alternatives

 

Effective drainage is essential in civil engineering projects, and the design is influenced by the required capacity, inflow rates, and the geometric configuration of the structure. Reduction factors are applied based on material and application. Drainage layers can be granular or geosynthetic, with granular layers using free-draining aggregates and geocomposites comprising non-woven geotextiles and drainage cores or pipes. This study aims to establish equivalency between granular layers and geocomposites in water drainage and gas transport, assuming equal long-term capacity under identical conditions. Despite reduction factors and safety margins, geocomposites significantly reduce drainage layer thickness compared to granular layers. The methodology adopted in this project is to present an equivalency design between granular drainage aggregates and drainage geocomposite and environmental benefit of using geosynthetics as a drainage design solution. This is supported by practical examples and environmental benefits such as reduced aggregate extraction, transportation, greenhouse gas emissions, and construction time for similar or better drainage capacity.

 

 

 

 

Stephan Fourmont, David Beamier, Lucie Benedito

Design and use of multi-linear drainage geocomposites for gas collection layers

 

 

Pore pressures generated by gas underneath a geomembrane can affect its integrity and the entire lining system. It can create whales/hippos in a surface impoundment, significantly reduce normal stress on the lower interface and create a veneer instability on final landfill cover. The membrane is lifted by the pressure of the gas trapped beneath it. The solution to avoid such occurrences is to install a permeable material that collects and transmits the gas outside the lining system. It can be vented to the atmosphere in the case of impoundments or collected in a gas collection network for valorization in case of landfills, for example. A sand layer is certainly possible, but drainage geocomposites offer an efficient and economical alternative. Depending on the application, the drainage geocomposite is designed to act as a passive system (no mechanical vacuum applied) or active. This paper presents the use of multi-linear drainage geocomposite for gas collection and its hydraulic behavior to collect and evacuate the gas. A case study is also given with the use of geocomposite as venting layer under a lined pond.

 

Carl Charpentier, Stephan Fourmont, Simon Allaire

Case study on a contaminated soil landfill in Canada with a focus on geosynthetic materials and electrical leak location

 

 

Designing a double-lined landfill for contaminated soils certainly presents several challenges. Many design aspects are taken into consideration to comply with local regulations, including thickness of the natural clay layer, minimal slopes for leachate drainage, side slopes for soil stability, global design to lower stress on the geosynthetics, and much more.
We will focus on the choice of geosynthetics used for the construction of a cell on a contaminated soil landfill during the summer of 2023, as well as quality control and quality assurance, including electrical leak location. A multi-linear drainage geocomposite was selected to cover each layer of an HDPE geomembrane and a layer of natural sand was also installed. It was not practical to use sand on the secondary geomembrane in the slopes due to stability and damaging risks, therefore the drainage system solely relied on
the drainage geocomposite. To carry on with the electrical leak location, a conductive mesh was added to the geocomposite installed in the slopes, allowing 100% of the installed geomembrane to be tested.

 

Y. RDISSI, S.FOURMONT, D.DIAS

Use of high-performance reinforcement geosynthetics to stabilize access roads

 

 

With the rapid infrastructure development, the availability of competent soils is decreasing. The access roads and tracks practicability should be ensured when crossing these weak soils. The practicability of access roads and tracks is therefore important. Depending on the mechanical properties of the subgrade, the construction of access roads requires the use of granular foundation materials of significant thickness, which can result in substantial costs and construction delays. This is especially true when the runway is to be constructed on soft subgrade and possibly in the presence of water. This article presents the use of a high-performance reinforcement geosynthetic to stabilize unpaved access roads, control settlement and prevent contamination between the subgrade and the foundation. A laboratory case well documented is used. Two calculation methodologies based on the subgrade soil characteristics are provided and compared.

 

J.Decaens, D. Beaumier, Stephan Fourmont

Lifetime considerations of geotextile UV exposure before installation

 

 

Geotextile are in most case intended for buried application, without exposure to sunlight. However, a short exposure to sunlight may occur before installation. Because of potential delay of installation and soil burying, the material is required to meet UV resistance. Artificial UV weathering will assess the potential risk of unintended exposure to sunlight. Photodegradation reactions consider the interactions with exposure conditions as well as polymer sensitivity to sunlight. Based on both laboratory measurements and field data, this paper evaluates the effect of light intensity, temperature and humidity with climates. Using polymer relation of its UV light sensitivity with the effective irradiance, a cumulative index is calculated for the reduction of geotextile service life from exposure to sunlight. Artificial weathering cycles for geotextiles are compared and related to the specific degradation mechanisms of polypropylene and polyethylene terephthalate. The reaction rate is correlated with temperature, respectively for each polymer. A model using radiant energy and temperature is proposed for guidance to service life prediction of partly UV exposed geotextiles.

 

Fourmont S., Pellez JC.

Innovative mechanically stabilized earth walls with geotextiles geocells

Structures reinforced with geosynthetics consist in increasing the mechanical performance of a soil (mainly shear resistance) by associating it with flexible geosynthetics inclusions. One of the important issues in the construction of geosynthetic reinforced walls is the supply of natural backfill materials with the required properties needed for the stability of the wall. Indeed, unlike geosynthetics that exhibit stable properties due to extensive quality controls during the manufacturing process, soil matrix will vary from a site to another and even from the beginning to the end of the excavation work. It influences the soil stability itself and also the soil-geosynthetic interface. As it minimizes the influence of soil characteristics on the stability of the reinforced structure, M3S geotextile geocells make possible, in addition to the construction of reinforced structures with complex shapes, to reuse the soil material excavated on-site to build the wall, including those with very poor geotechnical characteristics. This publication presents the M3S cellular system and its mechanical and functional characteristics. It also gives a case study on the construction in 2019 of two MSE walls as part of the A71 motorway bypass on the APRR network, France.

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