AUSTRIAN ENGINEERS are assessing the stability of a rockface after landslides in July forced 250 people from their homes on the outskirts of Schwaz, near Innsbruck.
Around 30,000m3 of limestone has broken away from the 80m high Eiblschofen since the hamlet of Ried was evacuated following the initial fall of around 50m3 of rock.
Dolomite mining on the mountain may have been the cause of the failure, although head of the Faculty of Mining Engineering at the University of Leoben Professor Horst Wagner said: '[The role of] mining activity is a matter of speculation at this time', adding there was circumstantial evidence that groundwater movement may have played a part in the collapse.
Up until the time of the incident, when mining stopped, dolomite was being extracted at the rate of 120,000t a year from inclined conical stopes up to 150m high. One stope, within 300m of the rock face, was abandoned in 1993 following an underground collapse. More recent mining has been on a smaller working face just 30m square. The stopes are partly packed with residue.
Assessment of water movement in the mountain is complicated by up to 1,000km of adits driven in pursuit of silver, copper and zinc for at least 500 years until the 1920s.
Seismic monitoring revealed activity between 0 and 0.2 on the Richter scale in March and June this year. Observations coincided with an unusual warm wind from Italy causing an early snow thaw and with very heavy rainfall that swept across Europe. 'Prior to the fall there was an increase in low frequency activity but the centre could not be located,' said Wagner.
Work has now started on the construction of three protective walls above Ried. The upper of the two containment walls will be 15m high and have a volume of 70,000m3. A lower 'deflecting' wall will have a volume of 7,000m3.
When the walls are finished next month, a decision will be made on whether to allow villagers to return to their homes.
Nigel Glass in Vienna