Conference Agenda

<p>The increasing demand to reuse excavation materials, to use soil in place or materials with high fine contents in the construction of Mechanically Stabilized Earth structures leads to the extensive application of soil stabilization technics such as lime, cement or fly ash treatment.</p>

<p>Soil treatment is an economical solution to exploit poor in-situ materials that cannot be implemented in their natural state. The treatment improves, in short terms, the physical parameters of the soils allowing its workability. However, such treatments also modify the chemical parameters of soil such as alkalinity in durable manner. The pH will remain well above 10 for very long period even at low dosage.</p>

<p>Most of the MSE structure reinforced with geosynthetic uses PET based products. It is well established that PET is only suited for soil having pH ranging from 4 to 9. In highly alkaline environment, the degradation mechanism is strongly accelerated particularly when mechanical stresses are applied on the material. </p>

<p>Then using PET in treated backfill is a clear risk for a structure integrity.</p>

<p>In this paper, we will propose an extensive review treatment technics detailing the evolution of the soil alkalinity with time, then we will provide technical data showing the performances of PET reinforcement materials when exposed to alkalinity in the conditions of reinforcement applications, finally we will propose alternative solution such as the use of PVA reinforcement material and present their performances.    </p>

This paper is part of a series focusing on the use of geosynthetics in Nordic climates. It focuses on sealing applications, while others in this series are addressing general considerations, and other functions of geosynthetics. In this paper, a review of the main concerns and performance requirements associated to the installation of geosynthetics for sealing applications is first pro-posed. These are essentially based on a review of the current practice, the interview of several installers specializing in the installation of geosynthetics in cold climates and a literature review. A strategy to assess the suitability of Geosynthetic Barriers in sealing applications under Nordic conditions is then proposed. The proposed requirements were drafted by the authors and ap-proved after revisions by a committee constituted of contributors to the ROUGH project. Guideline on the “Use of GeosyntHetics in Nordic conditions” are being prepared and will be published within the next months by the Nordic country’s authorities.

Considering the exogenous environment of the geotextile application, the characterization is more representative when tests and analysis are performed with sample exposed by sunlight or artificial UV light. Then, this paper aims quantitative evaluation of creep in specimens from field and laboratory degraded conditions. All analysis was done in two different types of geo-textiles differing by their weights and composition. Results obtained with the aged specimens were larger than virgin samples and varied according to the base polymer and weight. The be-havior of the aged materials did not show rupture results and the deformations were up to 40% greater. Thus, it can be concluded that simulating different conditions of exposure make the results more accurate as the application of geosynthetics in design and this makes the data from the studies more reliable for dimensioning engineering design.

<p>Samples of uniaxial geogrid were exhumed nearly 25 yr after construction of an instrumented steep reinforced soil slope in Norway. The samples were exhumed by a combination of machine and hand-excavation and, aside from surficial abrasions, exhibited no indications of adverse installation damage. Rapid loading creep tests were performed on the exhumed field samples, and the resulting load-strain-time data obtained to 10,000 h are reported as a series of isochronous curves. The isochronous curves for the field samples are compared with typical values reported for the geogrid by the manufacturer at the time of construction. The comparison shows creep strain increments over time periods of 1 to 100, 1 to 1,000, and 1 to 10,000 h in the field samples are in excellent agreement with the expected material behavior. The finding suggests the exhumed geogrid has experienced no degradation in tensile strength over the 25 yr service life in the steep reinforced soil slope.</p>

Designing with geosynthetics has been gaining market in recent years in different geotechnical and environmental applications. It is necessary to know its durability under degradation factors during the design life. This work evaluated the durability of geotextiles by simultaneous exposure to tensile creep and weathering for 90 days in the summer of 2020-2021. A polypropylene woven geotextile was used for research purposes for synergism durability analysis. Frames had a 22º slope to obtain higher global solar radiation. The creep load was set at 15% of the ultimate tensile strength. Laboratory tensile creep test was performed to evaluate synergistic degradation. Tensile creep tests with a 22° inclination proved effective in durability estimation by synergism between tensile creep and weathering. The study results have been promising in addressing the influence of the synergy of degradation factors and the achievement of partial reduction factors to apply in projects with geosynthetics.

Durability of waterproofing systems used in tunnels is of main importance because water highly influences durability, effectiveness and maintenance costs of underground structures. PVC-P geomembranes are one of the most applied technologies for tunnel waterproofing, nonetheless there is a lack of knowledge on their durability in underground applications. Even if long-term durability of PVC-P geomembranes has been analysed for outdoor applications (e.g. dams, roofs), few information are available for applications in underground conditions. In this paper the durability of two commercial PVC-P geomembranes for tunnelling applications is analysed based on the results on laboratory tests. Plasticizer absorption tests and mechanical tests are performed on the commercial geomembranes and on eight formulations of PVC-P specifically produced. The results of those tests permit to study the long-term degradation due to plasticizer loss and extrapolate the losses in time. Finally, an end-of-life time for the ge-omembranes has been defined merging mechanical requirements for the membrane and the long-term evolution of the degradation of the properties.

<p>The Buen Paso reservoir, located in the island of Tenerife (Spain), was waterproofed with a geomembrane of plasticized polyvinyl chloride, PVC-P with a polyester fabric. After 66 months, due to its poor condition, caused by a continuous and rapid loss of plasticizer, (bis(2ethhylhexyl)phthalate), it was decided to re-waterproof the reservoir with a high density polyethylene (HDPE) geomembrane, which was placed directly over the PVC-P geomembrane, without any kind of geosynthetic material between them. The placement of the two geomembranes, in direct contact, makes the Buen Paso reservoir an opportunity to study the possible interaction between the two geomembranes as well as the effects of this interaction on the durability of the HDPE geomembrane.</p>

<p>To carry out this study, the performance of the re-waterproofing HDPE geomembrane, the evolution of its main characteristics, and the detected pathologies have been monitored during a period of 246 months since its installation in the reservoir by conducting tests on samples extracted from different areas of the reservoir. Physical and mechanical characteristics, surface condition, oxidation induction time, surface oxidation, and environmental stress cracking resistance, have been studied. After 216 months, cracks began to appear in the crest of the reservoir, where the geomembrane is subjected to the highest stress, mainly in the north slope of the reservoir. Samples from that zone presented the greatest surface oxidation.</p>

<p>To study the interaction between HDPE and PVC-P geomembranes, samples of the PVC-P geomembrane were extracted under the HDPE geomembrane after cracks appeared, and the content of plasticizer was determined. It has been proven that it has lost more plasticizer and also the migration of plasticizer to the HDPE geomembrane. Being the plasticizer an ester, it could react with the products resulting from the oxidation that is taking place on the surface of the HDPE geomembrane, accelerating its degradation.</p>

The Galaube dam in France, is a 40 m high rockfill dam with an upstream face, built in 2001, operated by the “Institution des Eaux de la Montagne Noire” for storage and regulation of water resources. The upstream facing is ensured by a 4.6 mm thick bituminous geomembrane (BGM) directly laid on a cold mix layer and an impregnated layer gavel. A geotextile placed above the membrane provides puncture protection and drainage functions under fiber-reinforced concrete protective slabs.

During the construction, a series of control measurements were first carried out in the factory for each roll. The BGM was then installed by vertical strips, laid in one piece, and unrolled from top to bottom, so there were no horizontal joints. The vertical joints were subject to a strict quality control plan and all welding defects immediately rectified to guarantee the success of the membrane implementation as an impermeable barrier.

After 20 years of operation, analysis of the hydraulic behavior of the dam shows that piezometry is low and close to the natural terrain in the valley and on the banks, or close to the foundation downstream of the plinth and in the body of the dam. Monitoring of leakage flows, which are moderate (20 l/min in the drainage gallery) and show a continued favorable downward trend, confirms a very good behavior of the upstream facing and the absence of leaks through the membrane.

The proven behavior of the La Galaube dam, which has settled very few in practice (less than 4 cm) and has already undergone its first filling, a complete emptying in 2007, as well as 20 years of service without any observed defects and almost no maintenance operations, indicates that the design and construction of the upstream facing has been very successful.

The new norm EN 1997-3, that is the new EuroCode for Geotechnical Design, has is introduc-ing specific rules for the design of reinforced fill structures. Polymeric coated woven steel wire mesh reinforcement is treated in specific clauses, with Reduction Factors suited to this peculi-ar type of reinforcement. In facts a product with a metallic core and polymeric coating exhib-its different properties than Geosynthetics and fully metallic reinforcements. The present pa-per is aimed at presenting the durability criteria for woven steel wire mesh reinforcement and the way to derive the specific Reduction Factors defined in EN 1997-3. For design purposes it is required to address the concept of durability following mechanical and chemical damage. In practical terms this means that installation damage, as well as chemical degradation tests, are required for defining the Reduction Factors which need to be accounted for to reduce the ten-sile strength from the characteristic value to the design value. The paper presents the specific approach to durability for woven steel wire mesh reinforcement, for defining the Reduction factors for design.

<p>Geosynthetic Clay Limners (GCLs) have been an acceptable replacement for traditional natural liners such as compacted clay. Using GCLs has resolved many risks and uncertainties related to those additional lining systems such as permeability uniformity, cost, availability, sustainability, installation, and many more. The need for different products for different applications and design requirements led to development of GCLs since the beginning. Development of GCLs’ structure has continued by adding needle-punching and thermal locking to the manufacturing process, which resulted in the improvement of the internal shear properties. The improvement of GCLs continued with the focus on their components by producing GCLs with composite carrier geotextile to provide a higher interface friction and internal shear strength where required. As one of the most advanced developments, Multicomponent GCL were introduced. A Multicomponent GCL is a GCL with an attached geofilm, coating, or relatively thin geomembrane thereby decreasing the hydraulic conductivity or protecting the clay core or both. These advanced GCLs could reduce some of the risks allocated to standard GCLs and make the lining projects more feasible, efficient, and sustainable. Multicomponent GCLs such as Coated GCLs can reduce the risk of GCL desiccation specially in low confinement applications, protect the GCL against various potential risks such as Ian exchange with surrounding media, potential root penetration, internal bentonite erosion, downslope bentonite erosion, and bentonite piping, provide an immediate gas barrier, reduce the permeability of the lining system, and some more. These benefits have been investigated and discussed in various studies so far. This paper will review some of these advantages and related applications and provide an overview of the design requirements with coated GCLs with the focus on the long-term performance of these lining systems. This includes the long-term performance of the GCL and its components as well as the whole lining system.</p>