COMPLEX LANDSLIDE IN THE RJEČINA RIVER VALLEY

This paper presents the first phase investigation results of the complex landslide situated on north-eastern slope of the Rječina valley, between Valići damm and the village of Pašac. The valley slopes were formed in Paleogene flysch and Quaternary formations. The limestone rocks are present on the top sites, forming the scarps there. The complex landslide formation has been preconditioned by the geological structure and morphogenesis of the Rječina valley. This is the type of complex retrogressive landslide, starting with its development from toe to head. Thirteen individual landslide bodies were discovered on the slope. The material of slope formation and a part of weathering zone is caught by the landsliding. The larger part of landslide body is saturated by underground water penetrating through the covering zone in contact with flysch bedrock. The landsliding is relatively shallow, because there is no visible damage affected by sliding in the hydrotechnical tunnel, situated below the landslide toe. The mega-blocks of the limestone rock have also been moved and, most probably, are sliding down the flysch bedrock. This is a special phenomenon, atypical of the flysch slope landslide type in the area of Rijeka. The limestone rock on a scarp is extremely disintegrated, with new visible fractures in it. The site investigations comprised the surveying, seismic and engineering geological explorations. The surveying was performed by the method of terrestrial photogrammetry. The results are compared with aerial photos from 1981. In this respect, it was possible to discover the changes of slope morphology during the period 1981 — 1997. The photos were also used for the engineering geological mapping supplementation. The seismic surveying was performed by the surface seismic refraction method (the paper is published in Croatian)