Abstract
The soil shrinkage behavior of mineral substrates needs to be considered for engineering long-term durable mineral liners of landfill capping systems. For this purpose, a novel three-dimensional laser scanning device was coupled with (a) a mathematical-empirical model and (b) in-situ tensiometer measurements as a combined approach to simultaneously determine the shrinkage behavior of a boulder marl, installed as top and bottom liner material at the Rastorf landfill (Northern Germany). The shrinkage behavior, intensity, and geometry were determined during a drying experiment with undisturbed soil cores (100 cm3) from two soil pits; the actual in-situ shrinkage was also determined in 0.2, 0.5, 0.8, and 1.0 m depth by pressure transducer tensiometer measurements during a four-year period. The volume shrinkage index was used to describe the pore size dependent shrinkage tendency and it was classified as low (4.9%) for the bottom liner. The in-situ matric potentials in the bottom liner ranged between −100 and −150 hPa, even during drier periods, thus, the previously highest observed drying range (pre-shrinkage stress) with values below −500 hPa and −1000 hPa was not exceeded. Therefore, the hydraulic stability of the bottom liner was given.
Highlights
The growing world population is the major reason for an increasing amount of municipal solid waste (MSW), and engineered landfills with its low operation costs are still the first choice for global waste disposal in most areas of the world (i.e., Eastern Europe, India, China) [1]
The boulder marl consists is characterized by a sandy loam (SL) with a clay content between 9 wt% and 14 wt%, a slightly alkaline character with an organic carbon content (OC) between 0.02% and 0.12%; the Ks values decreased from 7.3 × 10−6 m/s to 4.1 × 10−7 m/s with increasing soil depth (Table 1)
The results allow to conclude that the shrinkage characteristics of the boulder marl including shrinkage behavior, geometry and tendency are mainly affected by the installation conditions and by the mechanical and hydraulic stresses
Summary
The growing world population is the major reason for an increasing amount of municipal solid waste (MSW), and engineered landfills with its low operation costs are still the first choice for global waste disposal in most areas of the world (i.e., Eastern Europe, India, China) [1]. In order to ensure these protective functions, the technical standards of landfill capping systems when considering the potential environmental impact of methane emissions and leachate percolation in the groundwater through leaking bottom liner are necessarily fixed in the country-specific statutory requirements [3]. Landfill capping systems are installed to restrain gas emissions (methane) and to minimize the leachate generation (infiltrated water contaminated with for example heavy metals) through (a) high available water capacity for the top liner (≥0.14 cm3/cm per meter) and (b) low permeation rates (
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