A research team from the Faculty of Engineering of the University of Porto (FEUP) is working on an innovative solution to prevent accidents in mining tailings dams.

This subject of analysing the stability of dams and large piles of mining tailings has been extensively studied at FEUP on the initiative of Professor António Viana da Fonseca, who has collaborated with various international institutions, particularly in Brazil, where this subject is of central importance.

Following the collapses of the Fundão dam in Mariana (2015) and the Córrego do Feijão dam in Brumadinho (2019), both in the Brazilian state of Minas Gerais, with human losses, the ruination of villages and extremely serious environmental damage, the international community has been looking for a new paradigm with new guidelines to regulate the construction, monitoring and ongoing risk assessment during the operation of these structures.

FEUP’s Geotechnics Laboratory, headed by Professor Viana da Fonseca, has sought to contribute to the development of best practices for characterising and modelling these materials and analysing the stability of structures, which have been translated into directives that have been implemented by regulatory bodies and companies that own, manage and build the sector.

From the research carried out at the Faculty of Engineering came the INPROVE project, which uses a sustainable cement to reinforce the stabilisation of these deposits by building structural zones with cemented filtered tailings, thus improving the stability of these large dams and piles. This solution could be implemented in new facilities, in remediation plans and the closure of existing structures, or to remineralise rich ore deposits with added value that have been accumulated over historical periods.

The INPROVE project’s solution proposes the use of a more sustainable binder than conventional Portland cement, through the alkaline activation of industrial waste, with a smaller environmental footprint.

Sara Rios, an assistant researcher at FEUP’s Civil Engineering Department and a member of the CONSTRUCT – Structures and Construction R&D Institute research unit, led this project, which was funded by the Foundation for Science and Technology (FCT).

According to the researcher, “through the optimisation of alkaline cement in conjunction with mining tailings carried out during the project, it was found that the cement porosity/volumetric content index makes it possible to obtain a good relationship between the mechanical behaviour of the mixture and its dosage. This index was therefore used in a simplified approach to calibrate a constitutive model extended to cemented materials.”

According to Sara Rios, the recently completed INPROVE project aims to contribute to reducing the number of accidents at mine tailings disposal facilities. “These facilities can be of various types, but the most dangerous are huge dams built by hydraulically depositing tailings upstream. The collapse of these structures results in the landslide of a colossal mass of earth (millions of cubic metres) which, being made up of mine tailings, can be polluting, and the release into the environment is extremely damaging.

In addition to the environmental aspect, there is an associated human aspect, as these accidents can cost human lives and cause serious environmental disasters, as has been seen over the last decade, adds Sara Rios. ‘These ruptures typically happen very quickly, with catastrophic consequences involving loss of human life and the destruction of towns and villages downstream, as happened in the most recent accidents at Mount Polley (2014) in Canada, Mariana (2015) and Brumadinho (2019), both in Brazil, at an overwhelming rate of hundreds of dams identified in the last 70 years.’

Nearly three hundred dead in the last decade

In 2014, the rupture of a mining tailings dam at the Mount Polley mine in a remote area of Canada flooded the local watershed with contaminated water and debris, releasing 25 billion litres of water mixed with mining waste – enough to fill around 10,000 Olympic-sized swimming pools. According to Environment Canada, the contaminants included 134.1 tonnes of lead, 2.8 tonnes of cadmium and 2.1 tonnes of arsenic, according to a Canadian inventory of harmful substances released into the environment, in what was, and remains, the worst environmental mine waste disaster in Canadian history.

In Brazil, the Mariana (2015) and Brumadinho (2019) disasters cost almost three hundred human lives, in addition to the environmental crisis they caused.

In Mariana, in the state of Minas Gerais, the Fundão dam collapsed and caused the deaths of 19 people and more than a million people without access to drinking water. It also dumped more than 40 million cubic metres of iron ore tailings in the form of mud, which travelled 663 km until it reached the sea, hitting 49 towns along the way.

In Brumadinho, also in the state of Minas Gerais, the collapse of the dam at the Córrego do Feijão mine, which had a capacity for 12.7 million cubic metres of tailings, generated a wave of waste that covered thousands of hectares and caused 259 deaths and 11 missing.