Multi-layered Cover System Research Articles

Probabilistic Translational Stability of Multilayered Cover System Based on Limited Experimental Data

Probabilistic Translational Stability of Multilayered Cover System Based on Limited Experimental Data

Geomembrane displacement monitoring system installed in a multilayered cover at the Aldermac mine site

The abandoned Aldermac mine site, located in the Abitibi- Témiscamingue region of Québec, Canada, is a former polymetallic mine that operated in the 1930s. Over the decades, the sulfidic mine wastes produced by the mine have been exposed to atmospheric conditions, leading to the generation of acid mine drainage (AMD) and contamination of the surrounding environment. In 2008–2009, reclamation works were initiated by the Québec government with the implementation of different techniques based on the characteristics of the different sectors of the mine site. In the southern sector, the production of AMD from the mine wastes pile is controlled by a multilayered cover system, including a 1.5 mm-thick textured high-density polyethylene geomembrane, aimed at limiting ingress of water and oxygen. In 2021, work was carried out to instrument the cover system with an innovative displacement measurement system that was developed and applied to the geomembrane along a sloping transect. The system allows continuous measurements of geomembrane displacement at three locations. This article discusses the installation of these instruments and presents preliminary results. Displacements over a 1-year monitoring period ranged from approximately 4 mm downslope to 32 mm upslope. This corresponded to strains ranged from approximately 0.01% contraction to 0.05% tension.

Enhanced Criterion for Selecting Surface Soils for Multi-layered Cover System

Enhanced Criterion for Selecting Surface Soils for Multi-layered Cover System

Hydraulic performance assessment of a multi-layered landfill cover system under constant water ponding

Abstract The engineered multi-layered cover system (MLCS) is used to minimize rainwater infiltration into the wastes accommodated in near surface waste disposal facility (NSDF). It is important to assess the hydraulic performance of MLCS before deploying it in the field. For this purpose, an instrumented three-layered soil column representing MLCS was subjected to 1.5 m constant ponding head for 400 days. The variation of volumetric water content and soil water potential was monitored as a function of depth and time. The objective of the study is to understand the long-term hydraulic performance and rate of saturation of different layers of MLCS. Under constant water ponding, the time to saturation for 0.3 m in surface layer, 0.6 m in drainage layer and 1.0 m in hydraulic barrier layer was observed as 24, 223 and 262 days, respectively. The numerical analysis of the MLCS predicted comparable time duration of 25, 234 and 272 days, respectively. It was noted that the numerical simulation performed by using measured wetting hydraulic parameters matched well with the experimental observation. The importance of soil specific calibration of water content sensors to improve the accuracy of observations was demonstrated. Percentage error in the estimation of layer specific soil water storage, clearly indicates that the volumetric water content measurements using profile probe was marginally better than 5TM measurements.

Vulnerable Interface Diagram for Translational Stability Analysis of Multilayered Cover System

AbstractTranslational failure of the multilayered cover system (MLCS) is a key issue encountered in waste containment facilities. This study extends the existing force-equilibrium method for analyz...

Long-term hydraulic performance of landfill cover system in extreme humid region: Field monitoring and numerical approach

Hazardous wastes disposed of in engineered landfills interact with rainwater, generate harmful leachate and may contaminate groundwater. To minimize this, a suitable multi-layered cover system (MLCS) is constructed over the buried waste. Field assessment of complex moisture dynamics in unsaturated MLCS and its long-term hydraulic efficiency has not been investigated in detail for extremely humid conditions (annual rainfall >1000 mm). Therefore, the overarching purpose of this study was to investigate the long-term hydraulic performance of a three-layered hydraulic barrier cover system under humid Indian conditions. The field cover setup was exposed to natural weather condition in the Northeast Indian state of Assam, for 800 days. The MLCS was instrumented to measure continuous variation of volumetric water content and matric suction as function of time and depth. The field measurements were used to determine the appropriate input hydraulic parameters and evapotranspiration model that can be used for numerical modeling. The results showed that simulation using drying van Genuchten soil-water characteristic curve parameters and Penman-Monteith evapotranspiration model matched the field observations. Events of the highest precipitation and extreme drought (cause for desiccation) did not lead to percolation in the drainage layer (60 cm) and barrier layer (100 cm). Numerical analyses performed for 87 years by considering the climate data of two different humid locations (Eastern and Western part) of India revealed that the progressive saturation of barrier layer occurred within 18 to 20 years. However, when geosynthetic clay liner was incorporated as additional barrier material, the saturation time increased by two-fold (42 to 44 years).

Erosion Potential of Compacted Surface Soils for Multilayered Cover System

Abstract Industrialization and urbanization have led to a rapid increase in hazardous and reactive wastes that need to be disposed safely. Multilayered cover systems (MLCS) are used for such waste disposal to impede contaminant interaction with the subsurface and atmosphere. Based on multiple forensic studies, soil erosion has been identified as a primary stressor of landfill covers that results in cover failure and exposure to contamination. The pinhole test is one of the most commonly adopted index tests to evaluate the erosion rate of soil. The main objective of this technical note is to measure the erosion potential of a soil at nine different compaction states and three runoffs, which correspond to three forms—rainfall-heavy, excessive, and cloudburst—that can result in significant erosion. A total of 729 pinhole tests on 9 different loamy soils were conducted in the current study, and the individual effects of initial moisture content, soil density, and runoff flow rate are discussed. It is observed that compaction of the surface layer for MLCS can be done at wet optimum moisture content with the highest possible soil density to minimize risk of erosion for all loamy soil. Furthermore, fine fractions of soils (percentage finer than 75 μm) was identified as a parameter that can be used to predict the maximum erosion rate of a soil using a simple linear relation.

Performance Evaluation of Profile Probe for Continuous Monitoring of Volumetric Water Content in Multilayered Cover System

AbstractA profile probe (PP) is a handy instrument for simultaneously measuring volumetric water content (θ) at shallow multiple depths in the field. The accuracy of the θ measurement is important ...

Long-Term Permeability Characteristics of Soil-Geosynthetic Combination Used in Landfill Covers

Abstract Multilayered cover system (MLCS) forms an integral part of engineered landfills nearing closure. Geosynthetic materials find multiple applications in MLCS as hydraulic barrier, drainage, separation, and filtration layers. Performance of geosynthetics used as filters needs to be well understood to ascertain the stability of MLCS. The main objective of this study is to investigate the compatibility of the soil-geosynthetic combination by long-term permeability tests. The compatibility of five different types of geosynthetics was evaluated with respect to two different gradations of red soil (RS) and RS–fly ash (FA) 50:50 mix. The results of long-term permeability and clogging characteristics were used to judge the effect of soil type, soil gradation, and type of geosynthetics on soil-geosynthetic compatibility. The efficacy of geosynthetics as filters was established based on (1) permeability improvement factor, which is defined as the ratio of the permeability of soil-geosynthetic composition to the permeability of the soil, and (2) stabilization time, i.e., the time required by the soil-geosynthetic system to achieve hydraulic equilibrium. It was noted from this study that the soil type and gradation had significant effect on the long-term permeability variation. The effect of the geosynthetic on the soil-geosynthetic combination is governed by its pore-size characteristics and was found to be marginal in this study. The stabilization time of a soil-geosynthetic combination increases with increase in soil fines content. The cyclic variation in permeability with time for a particular soil was found to be similar when different geosynthetics were used. Irrespective of soil type, higher permeability improvement factor was observed in the case of a woven multifilament geosynthetic and less in the case of a geocomposite. The class F FA in conjunction with RS was found to be compatible with the geosynthetics used in this study.

Frictional and Interface Frictional Characteristics of Multi-layer Cover System Materials and Its Impact on Overall Stability

The municipal and hazardous landfills nearing its design capacity need to be isolated from the atmosphere using multi-layered cover system (MLCS). These MLCS constitutes different layers of soil and geosynthetics with widely varying properties. Each of these layers fulfil specific requirements by acting as a surface protection, drainage, separation, filtration and hydraulic barrier layers of MLCS. Failure of these MLCS leads to waste–atmosphere interaction and results in extremely hazardous situation to biosphere. The stability of MLCS significantly depends on the shear strength characteristics of materials used viz., the internal frictional characteristics of individual soil materials and interface frictional characteristics of soil–soil or soil–geotextile combination. In view of this, frictional characteristics of four type of soils, four soil–geotextile interfaces and one soil–soil interface was determined using direct shear and modified direct shear testing methods. The modification of geomembrane used in barrier layer was also attempted, for improving its interface shear characteristics. The usefulness of the above parameters and the influence of its variability on the slope stability of MLCS of a near surface low level radio-active waste disposal facility (NSDF) is demonstrated in this study.