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 cm 3 ) 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.

Core Ideas Coatings determine the cation exchange capacity (CEC) of macropore surfaces. We predicted the millimeter‐scale, 2D spatial distribution of CEC at intact macropores. The approach combined infrared spectroscopy and CEC measurements of small samples. The CEC distribution in clay–organic coatings was similar for two different Bt horizons. During preferential flow in structured soils, solute transport is largely restricted to a complex network of macropores. Clay–organic coatings of macropore surfaces determine soil physicochemical properties relevant for mass transport and carbon and nutrient turnover, such as the cation exchange capacity (CEC). However, due to the lack of an appropriate measurement approach, the small‐scale spatial distributions of the CEC and its quantities are unknown to date. The objective of this work was to develop a method for predicting the millimeter‐ to centimeter‐scale, two‐dimensional spatial distribution of the CEC at intact macropore surfaces. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was used to analyze bulk soil and separated coating material and for intact macropore surfaces as DRIFT mapping. To determine effective CEC (CECeff), a reduction of soil mass down to 0.5 g for use in the standard barium chloride batch method was tested to account for the limited amount of soil material that can be separated from thin macropore coatings. Linear and partial least squares regression analyses were applied to predict the CECeff distribution at intact macropore surfaces for samples from Luvisol Bt horizons from loess (L) and glacial till (T) using DRIFT spectral data. The highest CECeff values were found for coatings and pinhole fillings rich of clay–organic material (L: 38 cmol kg−1; T: 29 cmol kg−1) compared with low CECeff values of uncoated cracks and earthworm burrows that were similar to those of bulk soil (L: 21 cmol kg−1; T: 14 cmol kg−1). The location of millimeter‐ to centimeter‐sized regions with increased CECeff levels at intact macropore surfaces corresponded with the location of clay–organic coatings. The proposed method allows determining the CEC at macropore surfaces to quantify their effect on nutrient transport by preferential flow as well as on plant nutrient supply in macropores that may serve as preferential growth paths for plant roots.

During a period of 4 years, soil chemical and physical properties of the temporary capping system in Rastorf (Northern Germany) were estimated, whereby compost was partly used as soil improver in the upper recultivation layer. The air capacity and the available water capacity of soil samples were first determined in 2013 (without compost), and then in 2015 (with compost) under laboratory conditions. Herein, the addition of compost had a positive effect on: the air capacity up to 13.4 cm3cm−3; and the available water capacity up to 20.1 cm3cm−3in 2015, in the recultivation layer (0-20 cm). However, taking into account the in situ results of the tensiometer and frequency domain reflectometry measurements, the addition of compost had a negative effect. The soil-compost mixture led to restricted remoistening even after a normal summer drying period in autumn and induced more negative matric potentials in the recultivation layer. In summary, the soil-improving effect of the compost addition, in conjunction with an increased water storage capacity, is undeniable and was demonstrated in a combined field and laboratory study. Therefore, intensive hydrophobicity can inhibit the homogeneous remoistening of the soil, resulting in a decreased hydraulic effectiveness of the sealing system.

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.

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