engleski

Lithostratigraphical investigations at the wider area of the Kostanjek landslide: review of existing data and planned activities

Geological model of the Kostanjek landslide was developed by Ortolan in 1996 on the basis of existing geotechnical investigations: engineering geological mapping from 1984 ; boreholes from 1931, 1972 and 1988 ; geophysical investigations in boreholes from 1988 and seismic reflection investigation performed in 1989. This landslide model is in use even today as a base for design of remedial measures. In the frame of the Japanese-Croatian scientific joint-research project ‘Risk Identification and Land-Use Planning for Disaster Mitigation of Landslides and Floods in Croatia’ model of the Kostanjek landslide is in use as a base for design of comprehensive integrated real time monitoring system aimed at landslide risk mitigation. Because of the poor data, the existing landslide model is relatively rough with questionable criteria for spatial correlation of rocks: stratigraphical identification of rocks and plasticity index of marls. Three sliding surfaces in four boreholes from 1988 (KS-2’, KS-3, KS-4, KS-5) are interpreted in the following way: (1) Sliding surface with maximum depth of 50 meters is identified at lithological contact between thickly and thinly bedded marls in Upper Pannonian rocks ; (2) Sliding surface with maximum depth of 65 meters is identified along thin layer of clay in thinly bedded marls in Upper Pannonian rocks ; (3) Sliding surface with maximum depth of 90 meters is identified at lithological contact between thinly laminated clayey marl and coarse grained rocks of Sarmatian age. In this paper lithostratigraphical column of the wider area of the Kostanjek landslide is given to reconstruct origin of rocks and relative positions of lithological units. Geological column presents informal formations at the surface of the Kostanjek landslide and in the shallow subsurface (0-400 meters) in the following order (from bottom to the top): Bizek fm., Dolje fm., Croatica fm., Kostanjek fm. and Okrugljak fm. Lithostratigraphical units of Miocene Epoch in rank of formation can be considered as unique and homogenous according to lithology. The short description of formations is given to explain geological origin of rocks and soils and to highlight the main characteristics which may influence stability of recent slopes. Planned geological investigations are given in the last paragraph. The aim of planned geological investigation at the area of the Kostanjek landslides is interpretation of the ground conditions as preparatory causal factors. Geological investigations will encompass: mapping of the lithofacies on the surface of abandoned cut face in marl quarry ; exploration of lithofacies in the subsurface by drilling of 1 borehole with coring (100 m deep) and by digging 18 investigation pits (1-1.5 meters deep) at the area of landslide ; and reinterpretation of lithofacies from four boreholes from 1988. On the basis of these investigations it will be possible to interpret 3D extent and spatial position of lithofacies bodies which are present at the area of the Kostanjek landslide. Unfavorable rock mass discontinuities (bedding, laminations, unconformities and sedimentary contacts) will be checked as possible sliding surfaces depending on relative position in landslide model and according to reinterpreted kinematic history.

lithostratigraphical units ; Kostanjek landslide ; Miocene sedimentary successions ; bedding ; unconformities ; sedimentary contacts

nije evidentirano