engleski

Dynamic and behaviour prediction of the grohovo landslide

Grohovo landslide is situated in the central part of the Rječina River Valley. Rječina watercourse is 18.7 km long and its river mouth is in the centre of Rijeka city. The central part of Rjecina River is 1.8 km long, and 0.8 to 1.1 km wide and it represents a narrow flysch valley between a karst plateaus. The Cretaceous and Paleogene limestone rocks are situated on the top of the slope, while the Paleogene flysch is situated lower on the slope, including the bottom of the valley. South-western slope of the valley is covered by predominantly coarse soils of limestone composition. Crown of instability is clearly marked by cliffs formed in limestone rocks which are much disintegrated and recently opened fractures are visible. On the north-eastern slope, slope deposits are mostly a mixture of clayey silt that was formed by weathering of flysch bedrock and fragments to blocks of limestone originating from the cliffs on the top of the slope. On both slopes, different types of instabilities, according to type of movement, type of material involved and state of activity, can be found. The biggest instability is Grohovo Landslide on the northern slope downstream of the existing accumulation. This landslide is not a recent phenomenon, because the data concerning mass movements has been registered on the end of the 19th and during the entire 20th century, last in December 1996. The field investigations indicated a complex landslide and evidence of many individual movements could be distinguished. These are identified as initial (primary) landslide, landslides in talus material, lateral landslides in soil material, reactivated landslide near the toe, sliding of separated limestone blocks and rock falls from the limestone cliffs. On the basis of the geological mapping and geophysical surveys, the thickness of the displaced slide mass could be estimated and the position of failure surfaces could be determined. The geometry of the landslide is described below, following the WP/WLI Suggested Nomenclature for Landslides (IAEG, 1990): Total length L = 425 m ; Length of the displaced mass Ld = 420 m ; Length of the rupture surface Lr =405 m ; Width of the displaced mass Wd = 200 m ; Width of the rupture surface Wr = 200 m ; Depth of the displaced mass: Dd = 6–20 m ; Depth of the rupture surface: Dr = 6–9(20) m ; In this complex/composite landslide, 13 slide bodies were identified in addition to mega-block movement and separation of blocks from the limestone scarps. The Grohovo Landslide was never stabilized with adequate remedial measurements. Conducted analyses indicate that the upper part of the slope, at the foot of the limestone scarps, has only a low factor of safety, such that in this part of the slope new movements can be expected in the future, e.g. when provoked by unfavourable hydrogeological conditions and/or strong earthquakes. In this paper we will present analysis of the landslide development from the sliding in December 1996. till today. Based on these analyses so as identified state of stability in particular landslide bodies, the behaviour of the landslide is predicted. According predictions, the monitoring plan is defined.

karst; flysch; mass movements; landslide; monitoring

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