Conference Agenda

<p>Waste disposal facilities (landfills) need to be designed with two distinct and complementary barriers, active and passive. In order to prevent contamination of subsoils and groundwater by the leachate provided by wastes, passive barriers need to be installed with very strict regulations. Nonetheless, with the luck of natural sites meeting regulations and considering economic and technical concerns, designers used to perform equivalency on a landfill geographical site by considering the potential environmental impact of wastes on water resources and aquifers. In this equivalency study, analytical and numerical analyses have been performed on relative concentration evolution of contaminants through the geosynthetic reinforced barrier and soil liner in comparison with conventional passive barriers in the same contamination configuration. Numerical modeling has been used to reproduce leakage and contaminant transfers into the entire barrier to the aquifer by SEEP/W and Ctran from Geostudio (2012). In this study, we found that the reinforcement of the passive barrier with a Geosynthetic clay liner (GCL) and the reduction of the low permeable layer thickness increased the performance of the whole barrier by limiting the evolution of the contaminant migration into the groundwater and subsoil as compared to the regulatory one. In conclusion, equivalency is possible for passive barriers; however it is important to pay attention to contaminant transfers and the amount they involve with time.</p>

<p>The stability of cover systems of landfills depends on the efficiency of the anchorage of the reinforcement at the berms or at the top of the slope. Due to the sloping configuration of a landfill, the pull induced on the geosynthetics of the cover system at the berm is in inclined direction. Four design methods, namely, Hullings and Sansone (1998), Koerner (2005), Qian et al. (2002), and Villard and Chareyre (2004) methods are widely used for veneer design. These methods primarily differ in their consideration of resistance at the bends at the inclined portion, and hence, there is wide variability among the predicted anchorage capacities. Among the four methods, Villard and Chareyre's (2004) method is the most comprehensive method. While other methods considered a frictionless pulley at the bends, Villard and Chareyre (2004) considered a weighting coefficient to account for the resistance at the bends due to a change in direction. However, despite the advancements made in the design methods, it was difficult to assess their verity in the absence of adequate field or experimental data.</p>

<p>To overcome this limitation, inclined pullout tests were conducted by the authors on veneer reinforcement (geogrids) anchored in different configurations. The experimental data were compared with the predicted anchorage capacities by the four methods; but, none of the methods could predict the anchorage capacities consistently. Thus, a new method is proposed which is a modification of the Villard and Chareyre (2004) formulation and is based on the determination of modification factor for the bend resistance from the back-analysis of the experimental results. The proposed improved methodology could satisfactorily predict the anchorage capacities not only for the experimental results by the authors but also with the previously reported lab and field data.  </p>

<p>The Bulera landfill is located in Larderello, province of Pisa, and is one of the few authorized landfills for hazardous waste in Italy, for over 1 million tons. In the year 2018 an expansion was decided adding additional volume above the old waste body temporarily covered, for total expected further quantity of 640,500 m³. The project involved many challenging problems which have been efficiently solved with the use of geosynthetics.</p>

<p>The inclined intermediate barrier was, at the same time, the capping of the old waste body and the bottom of the new one. It was necessary to study a multilayer system with geosynthetics capable to fulfill hydraulic (impermeabilization and drainage), mechanical (protection) and static requirements. With analogous approach also the final capping was designed.</p>

<p>Given that the landfill develops along the side of a hill, different stability problems were analyzed, either global, compound, internal and sliding stability scenarios. From these analyzes it was necessary to design a steep reinforced slope at the foot of the landfill with the use of high strength geogrids, in order to assure the stability of the entire system.</p>

<p>Furthermore, due to the presence of soft soils in the entire area, it was necessary to reinforce the base of internal roads with proper reinforcing geocomposites to allow the traffic of heavy vehicles.</p>

<p>At last, erosion control mats were foreseen to protect the slope of internal road embankments and the inclined soil layer of the final capping.</p>

<p>The works started in 2019 and the completion is expected after ten years.</p>

<p>The paper illustrates the problems faced and the criteria adopted for the choice of the different solutions with geosynthetics.</p>

<p>The Bulera landfill is located in Larderello, province of Pisa, and is one of the few authorized landfills for hazardous waste in Italy, for over 1 million tons. In the year 2018 an expansion was decided adding additional volume above the old waste body temporarily covered, for total expected further quantity of 640,500 m³. Even if the pre-existing landfill body was properly insulated, according with the Italian regulations, was not possible to lay directly new waste foreseen for the enlargement. An intermediate barrier had to be designed which was, at the same time, the capping of the old waste body and the bottom of the new one.</p>

<p>The regulation in force that time required, for hazardous waste landfills, a mineral clay layer with permeability K&lt;10^-9 cm/s and a thickness of minimum 5 m. Due to technical, environmental, and financial conditions a 5 m thick barrier was not practicable.</p>

<p>To overcome this obstacle, an equivalent mineral barrier system was studied, consisting of one meter layer of clay combined with special bentonite geocomposites.</p>

<p>The equivalence has been demonstrated with multiple methods and considering variable hydraulic heads to be able to identify the minimum characteristics required for the geosynthetic package used. The entire barrier system was completed with HDPE liner, drainage geocomposites and protective geotextiles nonwovens.</p>

<p>The barrier system has been approved by the Tuscany Region and some cells have already been made and tested successfully. The paper addresses, through technical data, dimensioning and construction experiences, the topic of hydraulic equivalence in barrier systems which is a very critical issue in landfills for hazardous wastes.</p>

The long-term performance of modern landfills is governed by a set of systems, including the landfill cover and the bottom barrier. In order to minimise the environmental impacts of a land-fill, a systems engineering approach may be adopted for the landfill design. Such an approach requires analysing the interactions between the different components of each system involved and then evaluating the response of the entire system assembled to quantify its overall engi-neering performance. The effectiveness of the lining systems is demonstrated through the veri-fication that the risk for human health and the environment due to pollutant migration is limited to an acceptable level. This risk is quantified through the calculation of the pollutant concentra-tion in the groundwater, which is expected to remain less than some prescribed level at a com-pliance point. The paper describes a simplified approach to the analysis of pollutant transport, which allows the pollutant concentration in the groundwater to be calculated under different boundary conditions and taking into account the role played by several geosynthetics, such as geonets, geomembranes and geosynthetic clay liners, which are used in landfill lining systems.

Although a number of studies have been devoted to the assessment of the leachate flow rate through defects in geomembranes, which are routinely used in conjunction with low-permeability mineral layers for the lining of waste disposal facilities, relatively little attention has been paid to the mechanisms that control the transport of contaminants. A theoretical framework is here presented to model the advective-diffusive transport of inorganic contaminants through defects of uniform width and infinite length (holed wrinkles, defective seams, etc.), whereby imperfect contact conditions between the geomembrane and the underlying mineral layer are considered, and the mass conservation condition is imposed for both the solvent and the solute phases. Closed-form analytical solutions have been derived to assess the contaminant mass flow rate for the cases of pure advection and pure diffusion, with a view to quantifying the error associated with the simplified calculation approaches that are currently adopted for the performance-based design of landfill composite liners.

<p>Geosynthetics are construction products used by a very large number of end-users and designers who can’t be experts in geosynthetics and need help. On top of that, a wide range of materials structures are available on the geosynthetics market to ensure the same function. That’s why, when they are faced to new/innovative type of construction materials like geosynthetics, a lack of knowledge leads engineers to be very fearful in the use of alternative solutions and products which don’t fulfill initial specifications at 100%. Moreover, in many cases, specifications are a copy paste of a technical data sheet in which all properties are not relevant for the given application, therefore, this prevents free competition without any technical reason. This is a win-win situation neither for the end user nor for the contractor. The information of geosynthetics market players is necessary to open as much as possible the door to all solutions that work well.</p>

<p>User guide of design standards in geosynthetics applications as proposed by the french IGS chapter and partially described in this paper will help geosynthetics market players by describing how to select relevant performances with the appropriate design data for the given application, and listing the justifications to be requested. Its purpose is not to establish design methods as done by ISO TR 18228, its purpose is to provide the way to check that the material will fit for the specific project conditions instead of the too usual non relevant product vs product comparison process.</p>

<p>This paper will consider usual waste landfill applications only, i.e. drainage, veneer reinforcement and soil-gripping in capping.</p>

<p>Hopefully, this paper could help to open markets and competition where specification is so strict that it is more or less impossible to suggest a technically relevant alternative solution to the specified product.</p>

<p>Geosynthetic clay liners (GCLs) are thin, hydraulic and chemical containment barriers with low hydraulic conductivity (≤ 3×10-11 m/s) to water or dilute chemical solutions. However, when used to contain liquids with more aggressive chemistries, the hydraulic conductivity of GCLs can be several orders-of-magnitude higher. Polymer enhanced ben-tonites (EBs) are developed for use in GCLs to maintain low hydraulic conductivity upon exposure to liquids with aggressive chemistries. Polymer loading is an important factor af-fecting the hydraulic conductivity of enhanced-bentonite GCLs (EB-GCLs). Measure-ments of polymer loading are conducted as part of manufacturing and construction quality assurance/quality control (QA/QC) of EB-GCLs, and to assist in interpreting outcomes of hydraulic conductivity testing of EB-GCLs. Methods used to quantify polymer loading of EB-GCLs are reviewed in this paper, with focus on loss on ignition (LOI) and total carbon (TC) analyses. Both methods may be component methods in that measurement of the pa-rameter of interest (i.e., LOI, TC) is required for the NaB and polymer components as well as the bentonite-polymer mixture. In addition, composite LOI and TC methods are de-scribed whereby the polymer content is determined directly via calibration of measured LOI or TC for an EB series with different, known polymer contents. Each method can be used without direct measurement of the base materials or calibration for use in QA/QC. Examples are provided from tests conducted with poly(acrylic acid), sodium carboxyme-thyl cellulose, covalently crosslinked poly(acrylic acid), and a bentonite polymer compo-site to illustrate the application, accuracy, and limitations of the methods..</p>

<p>The paper presents some results of settlement calculations performed following completion of an ecological waste landfill builded on collapsible soils (moisture sensitive soils). The results of the calculations are compared in the hypothesis of maintaining the conditions of natural moisture content of the collapsible soil and in the hypothesis of flooding the collapsible soil as a result of an imperfect sealing system. Starting from the requirements of the national legislation in force which imposes a slope of at least 1% of the drains that take the leachate from the landfill, after consuming the settling of the deposit, the position of the drain is analyzed to ensure the transport capacity of the leachate from the moment of opening the deposit and until its filling and consumption of the undercarriage under the load transmitted by the deposited waste. Another aspect dealed in the paper is related to the stretching effort that may occur in the geomembrane of the basic sealing system, as a result of the foundation ground settlement. The settlement calculations were performed according to the Romanian technical norms: "Normative for foundation of buildings on moisture – sensitive, collapsible soils, indicative NP 125: 2010" and "Normative regarding the determination of characteristic and calculation values of geotechnical parameters, indicative NP 122: 2010", which are correlated to the Eurocode 7.</p>

A composite bottom liner system consisting of a geomembrane over a geosynthetic clay liner (GCL) was constructed for a municipal solid waste landfill in California, USA, in 2004. The liner system then was left exposed without placement of overlying waste for over a decade. In 2016, samples of the GCL were exhumed from the sideslopes for laboratory testing. To investigate the impact of field exposure on the diffusion and membrane behavior properties of the bentonite, multi-stage through-diffusion tests were performed on the exhumed GCLs and a virgin specimen of the same GCL product. Membrane efficiency coefficients (w) and effective diffusion coefficients (D*) were measured for potassium chloride (KCl) source solutions. Preliminary results are presented to assess the impact of the long-term field exposure on diffusion and membrane properties of the GCL. Comparisons are drawn with the existing literature for diffusion and membrane behavior, which to date has been limited to testing of virgin GCLs.