engleski

THE CASE STUDY OF CONSTRUCTION QUALITY CONTROL OF GEOSYNTHETIC CLAY LINERS IN LANDFILL COVERS

Geosynthetic clay liners (GCLs) are factory- manufactured hydraulic barriers consisting of a mineral (usually bentonite clay) and geosynthetic component (geotextile or geomembrane). During the last decades the use of GCLs continuously increased in geotechnical, hydrotechnical and environmental applications mainly for containment and separation purposes. In the Republic of Croatia, GCLs were often used as final covers at old landfill sites during reclamation works. Depending on the type of construction, location and function, GCLs have to fulfill certain requirements defined by legal acts, national and international standards and project specifications. There is a large number of laboratory test methods that could be used for the characterization of GCLs or their mineral component. In order to prove the requirements for landfill applications, GCLs are subjected to the manufacturing quality control – MQC during production and construction quality assurance – CQA procedures (described in ASTM D 5899 and ASTM D 6495). The recommended tests, test methods and frequencies are given in the mentioned standards for the GCL components (clay, geotextile, geomembrane) and final product i.e. manufactured GCL (Erikson & Jesionek 2004). Among them, there are several methods related to the determination of index properties of GCLs mineral component and to the determination of hydraulic behaviour of finished product. Swell index test (ASTM D 5890) quantifies the swelling property of GCLs mineral component. Fluid loss (ASTM D 5891) is a quick method of determining the ability of GCLs mineral component to perform as hydraulic barrier. Hydraulic behaviour can be precisely determined by hydraulic conductivity testing (ASTM D 5887). According to some investigations, a low fluid loss value and a large swell index would imply preferable hydraulic behaviour i.e. low permeability of GCLs, as well. In the construction stage and during the envisaged lifetime of an landfill, the changes of certain properties of GCLs may occur. It could be caused by various conditions such as: type and thickness of cover layers, damage during installation, atmospheric conditions, GCLs mineral component interaction with biogas and leachates etc. This paper presents the results of laboratory testing’s of index properties (free swell and fluid loss of bentonite) and GCLs hydraulic conductivity on samples that were installed at one real landfill site for the period of three to nine years. All samples showed change of properties in relation to manufacturers’ declared values at the time of installation or control testing during construction stage. It could be explained by multiple possible causes such as: unfavourable climate conditions and modification of design solutions during installation stage ; cation exchange and desiccation of GCLs mineral component afterwards (Kosić et al. 2015). Surprisingly, the connection between the time of installation and the extent of the degradation of properties could not be established. Among the possible causes, the most likely one could be the different origin and mineral composition of bentonite clay used during production of GCLs. Beside, a huge variability has been noticed in the composition and height of cover layers. In conclusion, despite the well established procedures and methods for the construction quality control of GCLs used for the landfill cover applications, there still exist a need for further improvements especially in construction companies.

geosynthetic clay liners, MQC, CQC, index properties, hydraulic conductivity

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