Assessment of landslide hazard on flysch slopes

Landslides appearance is a geomorphological process associated with soil configuration and structure, hydrogeological parameters, climate and vegetation conditions in which they appear. Hazard represents the likelihood of landslide occurrence at locations with specific local conditions at specific time. Investigating numerous landslide appearances on slopes in flysch deposits, certain regularities regarding slope elevations, geolgical fabric of slope, properties of the soil material in the geotechnical profile, groundwater level and number of other conditions affecting slope stability in flysch masses were noted. This paper gives the review of noted regularities in landslide appearance and the estimation of the landslide occurrence likelihood at the Bakarac Channel in the flysch synclinal around Rijeka, Croatia. At Bakarac Channel location, based on longtime investigation works for different purposes, it was established that the wings and the base of the valley are made of flysch rock mass consisting mainly of silty marl, laminated silt to silty shale and fine grained sandstones, trimmed with superscripted limestone rock zones. Hazard assesment of this area was made based on slope elevation analysis, lithological composition and geological fabric, geotechnical properties of slope deposits and flysch bedrock, hydrological and hydrogeological conditions. Zoning according to the slope stability was performed dividing the area into four zones: stable terrain, eroded terrain, potentially unstable terrain and unstable terrain with landslide signs.