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Geomorphologic mapping and 3D modeling of theKostanjek Landslide

The Kostanjek landslide is located in the western residential area of the City of Zagreb at the base of the southwestern slope of Medvednica Mt. Since its activation in 1963, this landslide has caused substantial damage to buildings and infrastructure in the residential zone, as well as to factories and commercial buildings. According to the existing landslide model, the total area of the landslide is 1.2 km2, volume is 3.3 x 107 m3, and maximum depth of landslide mass is 90 m. In the frame of the Japanese-Croatian project it is planned to establish monitoring of the Kostanjek landslide and to develop early warning system for landslide risks. Three dimensional modeling of the landslide, aerial photogrametric interpretation and site reconnaissance of the landslide features is carried out as a first step of landslide risk assessment. In addition, preliminary geomorphological map of the Kostanjek landslide is interpreted. These studies resulted in the following conclusions: 1) There are several landslides (150 to 200 m width) at the west side of excavation carried out by the cement factory. In the tunnel, located north of the excavation face, it is recognized deformation zone from 84 to 102 m from the entrance, with slickensides oriented N 45° E 30-35° S (at 86 m from the entrance) and wall severely destroyed by external force from NW. No other significant deformation by external force is noticed after this zone to the end of the tunnel. 2) On the basis of orientation (strike and dip), slickenslides are extrapolated to the surface, in the three-dimensional model of the Kostanjek landslide using the software “ADCALC3D”. Intersection line between surface and slickenslide plane is located on the place where small landslide block is recorded by engineering geological mapping (west of excavation face). 3) On the basis of stereo interpretation of aerial photographs, one landslide body is assumed on the north side of the excavation with approximate dimensions: 500 m width and 800 m length. However, clearly visible head scarp of this large landslide block does not exist. 4) Inside the contours of existing landslide model, typical landslide topography is not recognized. However, few small landslide blocks are recognized in different positions. Special attention should be given to settlements along northern landslide boundary. In the frame of the project, the following activities are planned: drilling a deep borehole at the beginning of 2012 ; installation of monitoring equipment for detecting movements at the surface and in the underground ; detailed geomorphological mapping of landslide features with interpretation of landslide bodies. These investigation are aimed at derivation of landslide hazard map of the Kostanjek landslide.

aerial photogrametric interpretation; 3D landslide modeling; Kostanjek landslide; landslide mapping

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