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Our work aimed to determine the spatial distribution of the root cohesion of the roots of 8-year-old black locust and black poplar trees. The scope of our research and analyses included determining characteristics of root systems of the studied tree species by profiling the walls of a trench with a width and a depth of 1.0 m at a distance of 0.5 and 1.0 m from the trunks. Laboratory tests comprised determining the tensile strength of the selected root classes. A modified Schwarz model (RDM) was used to describe the horizontal distribution of roots in the soil. The increase in shear strength of the root-reinforced soil was determined by a strain bundle model in which the value of the force mobilized by the roots is described by the Weibull survival function (RBMw). The results of the root system measurements have shown that the black locust is characterized by a greater number of roots, while the roots of black poplar are thicker, which makes the relative surface of its roots larger. Calculations of root cohesion using the modified bundle model, taking into account the root system displacement, showed that the maximum value for the black locust was 9.4 and 6.4 kPa, and for the black poplar 6.4 and 6.2 kPa respectively at a distance of 0.5 and 1.0 m from the trunk. It was also shown that the optimal spacing of the trees of these species, necessary to achieve effective reinforcement of the soil, was approximately 4 m.
Aim of paper The aim of research was to determine the sensitivity of the impedance spectrometry method (EIS) to changes in electrical resistance of soil caused by water infiltration. Materials and methods Two types of mineral soil were considered in the research: fine sand and coarse silty sand. The research was to determine basic geotechnical properties of both soils (filtration coefficient, soil-water characteristic curve) and water infiltration tests in a vertical soil column. These tests included measuring changes in electrical resistance of soil medium, which were compared with observations of the location of the wetting front and numerical calculations of water flow through the soil. Infiltration tests were run for three soil samples. The first was a sample of medium sand, the second - coarse silty sand, and the third - medium sand in the lower part and coarse silty sand in the upper part. Results and conclusions The results of tests of electrical resistance of soils subjected to infiltration process in vertical column confirmed the significant impact of water in soil medium on its electrical conductivity. It has been shown that a change in soil moisture from an air-dry state to full saturation leads to a reduction of soil resistance by almost three orders of magnitude.
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