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M. Riot, C. Balland, P. Delmas, Pascal Villard, Maria Delli Carpini, F. Emeriault, S. Fourmont

Monitoring and warning system including a bi-modulus geosynthetic for the reinforcement of cohesive soil on cavities



The use of reinforcement geosynthetics to prevent localized collapses such as cavities is common today. Numerous experimental and numerical studies allow a precise understanding of the geosynthetics behavior related to these application. Within the REGIC (reinforcement by intelligent geosynthetics on natural or anthropic cavities) research project, an innovative solution has been developed and patented by the Afitexinov company. This solution includes a specific reinforcement geosynthetic coupled with an autonomous and remote warning device to detect a localized collapse or sinkhole. This innovative geosynthetic is an inverted bi-modulus reinforcement geosynthetic equipped with optical fibers. The first modulus at lower strength allows detecting possible deformations before transmitting the load to the second modulus with higher strength. This two-stages reinforcement system guarantees a high degree of safety from the start of the failure.

The new geosynthetic solution presented in this article aims to reduce the costs and time related to the installation of a monitoring system on a construction site. This solution’s installation and set-up do not require an expert on-site, thanks to a standalone monitoring box. This Preditect system is able to monitor large critical areas for ground deformations and detect potential underground failures. In case of any unexpected event, it will launch an automatic alert.

S. Fourmont, J-C. Pellez

Innovative mechanically stabilized earth walls with geotextile 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.

Erika L Erlandson, Ian R Fleming

Large-scale laboratory testing of the performance of geosynthetic mine waste covers



The low permeability of geomembranes has made them a useful material for preventing contaminant leakage from many containment facilities, such as landfills and lagoons. This same characteristic also makes them an attractive choice for cover applications, particularly in the mining industry. However, geomembrane covers have not been widely adopted due to a lack of published research on their effectiveness. To address this lack of research, a large-scale laboratory study was done to quantify the amount of leakage obtained through a defect in a geomembrane cover. The leakage rate was assessed for a variety of slope angles, rainfall rates, surface microtopography, and defect sizes, shapes, and locations. The leakage rate was found to depend on all of these factors to varying degrees.

E. Tardif, J. Khamisse, P. Gendrin

Leachate drainage by technical geocomposite at Sofa sanitary landfill



In 2018, the Municipal Development and Lending Fund of Palestine started the construction of Sofa sanitary landfill at Al Fukhkhary. The lining system of the bottom was initially constituted of a 2mm-thick HDPE geomembrane, a protective geotextile and a 0.45m-thick gravel draining layer, on a surface of around 60000m2. A design has been made to propose a drainage geocomposite with mini-pipes Draintube, able to have the same hydraulic properties as the draining layer. The choice of the product considered the whole geometry of the project (waste thickness, geometry of the bottom…) as well as the project requirements (mechanical specifications, etc.), as it also provides a mechanical protection of the lining system. Using geocomposite with mini-pipes allowed to save 27000m3 of draining gravel. In addition, the technology of this geocomposite with mini-pipes avoids biological clogging and thus guarantees its efficiency through time. In order to create a prefilter between the geocomposite with mini-pipes and the waste, a 0.15m-thick protective layer has been installed. By calculating the retention criteria, it has been shown the adequation between the opening size of the filter of the geocomposite and the sieve analysis of the protective layer.

P. Saunier, E. Blond

Lessons Learned on the Performance of Multi-Linear Drainage Geocomposites for Mining Applications



Tailings dewatering is a permanent concern for responsible mining companies. Soft and wet tailings can generally lead to stability issues in retaining ponds or dams, excessive environmental footprint because of their high water content and therefore a high volume to storage, and finally can increase the total process costs to a level that can eventually break the fragile equilibrium of the operation. This situation has become among the key issues to be solved, with higher environmental pressures and regulation authorities, as well as a market struggling since almost a decade. Traditional drainage geocomposites are commonly used in applications where the flow to be drained is average, the loads on the product are in the order of 500 kPa and the fines content of the soil to be drained is low. This paper presents a review of laboratory evaluations conducted on Multi-Linear Drainage Geocomposites (MLDG) to assess their applicability in tailings dewatering. Three studies were conducted. First, transmissivity tests were performed under very high normal loads, up to 2MPa, to reflect normal loads actually experienced in tailings and dams. Long‐term flow tests were then conducted during 90 days. In addition, filtration tests modeling the mechanisms involved in the deposition of tailings in a slurry form were performed, using a modified version of ASTM D5101. A scale test has been conducted in Morocco accordingly. All these tests were found to be conclusive and confirmed the applicability of MLDG for tailings dewatering applications. A case study of a recent project in Canada will be presented as well.

E. Vial, M. Vanhée, S. Fourmont

Multi-linear drainage geocomposite for sub-slab depressurization and radon mitigation



Sub-slab Depressurization (SSD) aims to reduce building occupants’ exposure to toxic gases from the soil. These gases can either be generated from contaminated soils (like Volatile Organic Compounds or Landfill Gas) or naturally present in the soil (like Radon). The SSD system is composed from the bottom to the top of a separator geotextile, a drainage layer, and a vapor barrier. One or more gas pits are located according to the gas concentration in the area and to the geometry of the building. Because most of the SSD systems are constructed in high-density population areas (e.g., new construction in old industrial zones), the truck traffic and the noise resulting from the excavation works, and the transportation of granular material is a nuisance for residents. It also damages the local road network that is not designed to handle heavy vehicles traffic. This paper presents the sizing and the use of multi-linear drainage geocomposite as part of the SSD system providing separation and gas collection functions. The geocomposite is composed of non-woven geotextile layers incorporating perforated mini-pipes regularly spaced and running the roll length. It is connected to a collector pipe and to the gas pit. It collects the soil gas and reduces the head losses thanks to the high-density network of perforated mini-pipes within the product and the specific fittings used to connect the product to the main collector pipe. The sizing of the geocomposite is done using laboratory tests and software to characterize the flow capacity and the head losses of the system. Multi-linear drainage geocomposites have been found to be efficient for both passive and active SSD systems.


The AFITEX Group