engleski

Landslide Occurrence Prediction in the Rječina River Valley as a Base for an Early Warning System

The Grohovo Landslide is a reactivated complex landslide in the outback of the City of Rijeka, Croatia. Several historical episodes of landslide movements and consequences demonstrate the needs for a landslide forecasting and an early warning system in order to reduce related hazard and risk and to protect human lives. The part of the Rječina River Valley between the Valići Reservoir and the Pašac Bridge is the most unstable part of the City of Rijeka area, with a highest hazard of possible sliding. Numerous historical descriptions, figures and maps describing landslides were found in the Croatian State Archive in Rijeka. An early warning system for possible landslide occurrence and assessment of landslide risk in the Rječina River Valley should be established based on possibility of prediction of instabilities appearances in the zones where the monitoring equipment is installed. Prediction of possible movements would be carried out on the basis of the results of 2D or 3D landslide stability analyses of wider landslide area in combination with the results of existing monitoring data. Critical limit values must be also defined for indicating of new sliding appearance and starting up the alarm. The 3D landslide stability analyses enable indication of possible hazard and risk for further landslide occurrences under unfavorable hydrological conditions in the most unstable part of the Rječina River Valley. The 3D stability analyses were carried out using landslide simulation model software LS-Rapid. LS-Rapid software could integrate the initiation of the landslide process triggered by rainfalls and the development of sliding due to strength reduction and the entrainment of deposits in the run out path. Stability analyses are based on strength parameters obtained by laboratory test on soil samples taken from the zones in which should be developed sliding surfaces. Soil testing were conducted on representative samples in a portable ring shear apparatus ICL- 1 designed for testing the residual shear resistance mobilized along the sliding surface at large shear displacements under static and/or dynamic local conditions. The results of the ring shear tests are necessary to enable input data for analyses of the development and propagation of the sliding mass in LS-Rapid software. In this paper will be presented deterministic 3D stability analyses using LS- Rapid software applied on the wider zone of the Grohovo Landslide at the north-eastern slope of the Rječina River Valley. The results of these analyses enabled prediction of possible sliding zones so as critical groundwater conditions (expressed by saturation ratio) those will cause sliding. Critical groundwater conditions could be connected with precipitation values, run off coefficients and infiltration ratios and these correlations will be used as an indicator of possible sliding in an early warning system. The most important indicators for alarm decision should be measured values on installed monitoring equipment in the moment when measured values reach proposed critical values.

landslide; early warning system; stability analyses

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