Shrinkage Characteristics of Boulder Marl as Sustainable Mineral Liner Material for Landfill Capping Systems

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.

Effect of artificial soil compaction in landfill capping systems on anisotropy of air‐permeability

“…3 and 4) and therefore less pronounced differences in pore size distribution following Groenevelt et al (1984). This predominant isotropic behavior also indicates the beginning of the proportional shrinkage phase as mentioned by Beck-Broichsitter et al (2018b, 2018c followed by changes in the inter-aggregate pore space; the stage is also characterized by the formation of additional vertical and horizontal tensile and shear-induced shrinkage cracks (Chertkov, 2014). Note that the differences in blocked air-filled pore spaces between non-rigid and rigid conditions (Tab.…”

“…The undisturbed soil cores were derived from two soil profiles of the mineral capping system that is subdivided into a recultivation liner [organic matter-rich topsoil (0-0.05 m), an intermediate, organic matter-poor layer (0.05-0.4 m), and organic matter-poor subsoil (0.4-0.7 m)] and a sealing liner (0.7-1.0 m) that consists of differently compacted glacial till (Beck-Broichsitter et al, 2018b, 2018c. The first 0.05 m of the soil profile are characterized by a crumbly structure, while a prismatic-platy structure is predominant in 0.2, 0.5, and 0.8 m depths.…”

“…The soil volume change was estimated simultaneously at each of the stages along the drying curve with a laser triangulation method, developed by Seyfarth et al (2012) and tested by Beck-Broichsitter et al (2018b). The line laser CMS 106 with a wavelength of 0.66 μm (Control Micro Systems, Orlando, FL, USA) senses the cylindrical surface of the rotating soil sample assuming the rotation center at the z-axis.…”

“…The concept of critical matric potentials describes the shrinkage‐induced volume change of layered‐installed glacial till of a mineral capping system in Northern Germany ( Beck‐Broichsitter et al, ). In the latter study, a critical value of the matric potential, ψ m * (hPa), was characterized as the beginning of the proportional shrinkage phase ( i.e ., change in void ratio ≈ change in moisture ratio) at ψ m * = –150 hPa to –300 hPa in 0.05 m soil depth and at approximately ψ m * = –300 hPa to –500 hPa for the glacial till layers in 0.2 m, 0.5 m, and 0.8 m depths.…”

“…However, in case of intensity parameters, pore rigidity is frequently assumed although questionable under laboratory and field conditions (Horn et al, 2014). In fact, a shrinkageinduced volume loss between 4.9% and 7.2%, for of example differently compacted soils (ρ b 1.86 g cm -3 ) following Beck-Broichsitter et al (2018b), would be interpreted as water loss if pore rigidity is assumed. Soil compaction increases the internal soil strength and makes the soil mostly more rigid (Horn and Smucker, 2005), especially when the Proctor optimum is reached, resulting in low shrinkage-affected volume change (Moon et al, 2008) and low k a -and a -values.…”