Integral bridges, jointless?
Integral bridge design offers the advantages of structural monolithism because of the absence of joints and bearings makes construction easier and faster, and also results in maintenance savings.Read more
04-05-2018 | Posted by Joaquín Martí
On April the 25th, 1998, Spain woke up to be shaken by the news that the dam bounding the Aznalcóllar tailings pond had failed. The disaster released about 1.3million m3 of mine tailings and some 5.5million m3 of contaminated water into the Agrio river, not far upstream from the Doñana national park.
Principia were hired as expert witnesses by Boliden, the owner of the facility, and now, 20 years down the line, it is worth recalling some lessons, lest we forget them.
The failure itself was truly spectacular: some 700m of dam, together with the top 15m of the ground, moved a distance of up to 60m before stopping. Why did the dam fail? And what can we do to prevent such failures in the future?
At a technical level, the reasons for the failure are clear. The dam did not fail because of an external event, such as an earthquake, explosion or flood. It did not fail because of poor workmanship or because the built structure did not conform to the original design. The dam was actually destined to fail from the very start, simply because the design calculations did not incorporate the true characteristics of the underlying ground.
The dam sat on about 4m of alluvial deposits underlain by 70m of blue marl. Two major features of the blue marl were not taken into account:
If the low permeability had been taken into account, the marl would have never had a chance to display its brittleness.
The two aspects above were the cause of the failure. But how can one explain the fact that, rather than simply developing a few cracks, the failed dam managed to travel a distance of up to 60m? This happened because, upon the failure of the dam, its initial movement caused the tailings behind it to liquefy, which had two consequences:
No doubt disasters will continue accompanying the history of mankind, but the lessons learned from the past will hopefully make them less frequent and serious in the future.