Stability assessment of Bojni ky landslide area based on geophysical ERT and geodetic GNSS measurements

With the development expanding into the unstable hillslope areas under the pressures of increasing population and urbanization, extremely rainfall due to climate change and human activities such as deforestation or excavation of slopes for road cuts and building sites etc. have become important triggers for landslide occurrence with negative consequences. Stability of slopes is one of the basic engineering problems in the building constructions and design. Slope deformation near Bojni ky village is part of the large landslide area of the western boundary of Nitrianska pahorkatina Upland, between the towns of Hlohovec and Sere . Moreover, these landslides should be in contact with the perspective construction of planned Water Work Hlohovec–Sere . Selected landslide part of Bojni ky has been periodically monitored since 1993 within project of Ministry of Environment “Partial Monitoring System of Geological Factors of Environment in the Slovak Republic“. In the selected landslide, there were realized the geophysical measurements using multicable, and GNSS measurements during period of 2010–2012. Geotechnical model was created on the base of resistivity data and lithology from existing boreholes. The results of stability analyses and GNSS monitoring of surface changes by a network of observed points indicate the instability of whole landslide body. The instability of slope has been proven in the central part of landslide, where the degree of stability was less than 1.1 even at dry condition (without influence of groundwater). Also, the results of geodetic GNSS measurements suggest increased activity particularly of partial scarp zones (points HSJ-37A and HSJ-38). The major measured changes of monitored points were detected just after the extreme precipitation fallen in the area in June 2011 (80.6 mm). Based on stability′s research the landslide has been considered to be the unstable, which was documented not only stability analyses but also position and elevation changes of observation points.