International Geologiical Congress - Oslo 2008

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GHZ-11 Rock slope movements and early warning of catastrophic failure and related tsunamis

 

Geocryological characteristics and warninc system of large rock glaciers failures

 

Galina Bondarenko, Research Institute of Foundation and Undeground Structures namedafter M.N.Gersevanov (Russian Federation)
 

 

Rock glaciers occur at permafrost zone of mountainous areas and subdivide into natural and technogeneous. Natural rock glaciers widespread, for example, at Norway mountains, especially north from the Polar circle. They are confined to highlands where permafrost is prevalent. The rock glaciers are large-scale congregations of coarse detritus cemented by ice and they have capability for self-maintained movement, which is caused by ice inclusion plastic deformations. This hazardous phenomenon requires early warning system of the avalanche-like collapses. Author has developed such methods for technogeneous rock glaciers. Processes of sliding and avalanche-like collapsing of technogeneous glaciers - frozen dumps accumulated on slopes - take place at some mines in northern and northeastern areas of Russia. These dumps are frozen and incorporate ice, firn and snow. The most studied cases are at the dumps of the apatite open-working in Khibiny at Kolskiy Peninsula. 14 case studies have been analyzed. Their failure was preceded by the longtime deformation. During landslide formation dumps' accumulation continued. Curves of dumps sliding depending on time have been plotted based on continuous surveyor measurements. The results of experimental researches of frozen soils and dump deformations show that their sliding is stipulated by ice plastic character. It is a rheological process that includes a stage of stationary flow with steady speed and a progressive flow stage. The sliding regularity has been ascertained.
Design values of friction, adhesion and viscosity factor has been received experimentally taking into account temperature and loading time interval. It has been shown that sliding velocity increase with increasing of the foundation slope angle, sliding layer thickness and its temperature. Dump sliding velocity prediction taking into account design characteristics showed good agreement with real flow velocities. Prediction of avalanche-like collapse that was done by the graph-analytic method using the dump sliding curves showed good correlation with real data. The obtained deformation pattern and the developed method of technogeneous rock glaciers of sliding velocity and the collapse time prediction can be used for development of a natural rock glacier collapse warning system. The warning system should be based on: study of regional peculiarities and their influence on rock glaciers distribution and thermal regime, data on soil composition, plane and deep structure, surface movement data, deformation pattern and design scheme, strength and strain properties of frozen rocks, deformation processes, quantitative or qualitative forecast of sliding and collapse. Taking into account difficulties of full research complex for warning system the presentation is focused on the collapse forecast method based on the monitoring of the specific points marked on glacier surface

 

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