Potential landslide hazard in a zone of stabilised earthen embankments illustrated by Wysoka Górka in Chełm

Plant cover is an important element in the management of earthen structures and slopes improving their aesthetic values and limiting their vulnerability to denudation processes. With regard to landslide hazards, an important aspect in the presence of plants is the effect of their root systems on the shear strength of the substrate and, consequently, on slope stability. The aim of the study was to determine the impact of the tree cover at the Wysoka Gorka archaeological site on the stability of the earthen embankment on Gora Katedralna in Chelm (Lublin Province). These architectural elements originate from the times of Chelm’s glory in the fist half of the 13th century, when it became the capital of Halych-Volhynia Duchy and a residence of Prince Danylo Romanovych (Isaiecic 1999). The research involved identifiation of the geological structure of the embankment (surveying, measurement of the fitration coeffiient) and laboratory determination of the geotechnical parameters of the soil (particle size distribution and soil compressive strength measured in a triaxial compression apparatus). In the next stage of the study, stability was calculated with limit equilibrium methods in the GeoStudio program. Standard calculations of the embankment stability were performed and the stability coeffiient for the slope devoid of vegetation and the tree-covered slope were compared assuming zero suction pressure. The shear strength parameters of soil reinforced by plant roots were adopted following the recommendations specifid by Hubble et al. (2013). The authors performed a probabilistic analysis in order to determine the probability of critical values of the safety factor (