Mine Tailings Storage: Safety Is No Accident

Val di Stava dam collapse Val di Stava dam collapse

Prestavel mine Prestavel mine

In July 1985, the embankment of the upper decanting basin dropped, causing the collapse of the lower one as well. This released a mass of about 1 80 000 m 3 of water and mud pouring at a speed of about 90 km/h in the valley below. Along the route, another 40 000-50 000 m 3 of erosion caused the destruction of buildings and hundreds of trees. In July 1985, the embankment of the upper decanting basin dropped, causing the collapse of the lower o e as well. This rel ased a mass of about 1 80 000 m 3 of water and mud pouring at a speed of about 90 km/h in the valley below. Along the route, an ther 40 0 0-50 000 m 3 of erosion caused the destruction of buildings and hundreds of trees.

I TALY I TALY

Basins Basins

Stava Stava

Mudflow caused the death of 268 people (including 59 under-18s), the complete destruction of 3 hotels, 53 houses, 6 sheds and hundreds of trees. In addition, 8 bridges and 9 heavily damaged buildings were demolished. A layer of mud between 20 and 40 cm thick covered an area of approximately 435 000 m 2 for a length of 4.2 km. Mudflow caused the death of 268 people (including 59 under-18s), the complete destruction of 3 h tels, 53 houses, 6 sheds and undreds f tr es. In addition, 8 bridge and 9 heavily dama d buildings wer demolished. A layer of mud between 20 and 40 cm thick covered an area of approximately 435 000 m 2 f r a length of 4.2 k .

Prestavel mine Prestavel mine

Basins Basins

Break area Break area

Stava River Stava River

Altitude (m) Altitude (m)

UPPER BASIN UPPER BASIN

LOWER BASIN LOWER BASIN

1 380 1 380

Most critical break area Most critical break area

Fluvial-glacial substrate Fluvial-glacial substrate

1 350 1 350

Gravel core Gravel core

Gravel core Gravel core

Topographic profile after the collapse Topographic profile after the collapse

1 310 1 310

0 0

100 100

200 200

Distance (m) Distance (m)

The cause of the collapse was identified in the chronic instability of landfills , and in particular the upper basin, which did not have the minimum safety coefficients needed to avoid the collapse. In over 20 years, landfills were never subjected to a series of stability checks. Among others, the causes of instability have been identified in: - the humid nature of the soil, which did not enable sludge drainage; - the incorrect construction of the upper reservoir embankment and in the proximity to the lower one; - the excessive height (34 m) and slope (up to 40°) of the embankment; - the incorrect location and maintenance of the overflow pipes of decanting waters. The cause of the collapse was identified in the chronic instability of landfills , and in particular the upper basin, whi did not have the minimum safety coefficients needed to avoid the collapse. In over 20 y ars, landfills were nev r subjected to a series of stability ch cks. Among others, the causes of instability have been identified in: - the humid nature of the soil, which did not enable sludge drainage; incorrect construction of the upper reservoir mbankment nd in the proximity to the lower one; - the excessive height (34 m) and slope (up to 40°) of the embankment; incorrect location and m intenance of the overflow pipes of d canting wat rs.

Tesero Tesero

L ÓPEZ , 2017 250 m L ÓPEZ , 2017 250 m

Avisio River Avisio River

Sources : Fondazione Stava1985 (http://www.stava1985.it); Chandler J, Pellegrini M and Tosatti G, 1995, Le cause del disastro, in Lucchi G (eds), "Stava: Perché la genesi, le cause, la responsabilità della catastrofe di Stava negli atti dell'inchiesta ministeriale e nelle sentenze del procedimento penale", pp. 221-230, Curcu & Genovese, Trento. Sources : Fondazione Stava1985 (http://www.stava1985.it); Chandler J, Pellegrini M and Tosatti G, 1995, Le cause del disastro, in Lucchi G (eds), "Stava: Perché la genesi, le cause, la responsabilità della catastrofe di Stava negli atti dell'inchiesta ministeriale e nelle sentenze del procedimento p nale", pp. 221-230, Curcu & Genovese, Trento.

Figure 12. The Val di Stava tailings dam failure

35