Abstract
The effects of compaction on soil shrinkage behavior need to be considered for engineering long-term durable mineral liners of landfill capping systems. For this purpose, a new three-dimensional laser scanning device was coupled with a mathematical-empirical model to simultaneously determine the shrinkage behavior of a boulder marl (bm) and a marsh clay (mc). Therefore, both materials were precompacted in 200 soil cores (100 cm3) on the basis of the Proctor test results with five different degrees of compaction (bm1-bm5; mc1-mc5). Thus, the shrinkage behavior, intensity, and tendency were determined during a standardized drying experiment. The volume shrinkage index was used to describe the pore size dependent shrinkage tendency and was classified as high to very high (11.3–17.7%) for the marsh clay and medium (5.3–9.2%) for the boulder marl. Additionally, only the boulder marl (bm2), compacted up to 88% of Proctor density, could be installed as landfill bottom liner in drier locations if the local matric potentials did not exceed the previously highest observed drying range (i.e. values below −300 hPa), to avoid crack formation and generation.
Highlights
Landfills still represent the major option for global waste disposal in most areas of the world [1]
The German Landfill Directive, which was enacted in 2009, includes the essential statutory requirements to achieve the securing of closed landfills: (a) available water capacity of the recultivation, requirements to achieve the securing of closed landfills: (a) available water capacity −of9 the or rather, topsoil layer of at minimum 0.14 cm3 /cm3 per meter, (b) Ks values of at least 5 × 10 m/s recultivation, or rather, topsoil layer of at minimum 0.14 cm3/cm3 per meter, (b) Ks values of at least equal −9to 0.5 m thickness and a hydraulic gradient of I = 0.3 m, and (c) air capacity (AC) values of at minimum
The results allow us to conclude that the soil water retention characteristics and shrinkage behavior, tendency, and intensity of both tested materials are affected by (a) the degree of compaction and (b) the corresponding water content
Summary
Landfills still represent the major option for global waste disposal in most areas of the world [1]. The major aim of a landfill capping system is to restrain gas migration (e.g., carbon dioxide and methane), to minimize leachate generation in order to protect groundwater (precipitation contaminated with heavy metals or polycyclic hydrocarbons) by (a) high water storage capacity for the recultivated layer and (b) low hydraulic conductivity and negligible small shrinkage-crack formation potential for top and bottom liners [4,5]. The plant-available water capacity and saturated hydraulic conductivity are considered essential properties of mineral sealing substrates (i.e., boulder marl and clay) according to a past paper [2]. These substrates are often used as landfill liners in combination with geosynthetics and geotextiles to ensure long-term hydraulic stability of the landfill capping systems [5,6]. The primary function of the bottom liner is not guaranteed if the actual, critical matric potentials within the mineral substrates are more negative than the pre-shrinkage
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