Downstream designs start with an impervious starter dam. Tailings are then discharged into the dam and as the embankment is raised, each new wall is constructed and supported on top of the downstream slope of the previous section, so the dam crest moves downstream with each raise. The downstream design was developed for areas with seismic activity and high rainfall or water collection.
Upstream construction begins with a starter dam. The tailings are then discharged into the facility where they form a tailings beach. The deposited tailings adjacent to the dam wall is allowed to drain and then can be compacted to be used to form the foundation for subsequent levels of the wall as the dam is raised. As such, the crest of the dam moves upstream with each raise.
Upstream tailings dams need to be raised slowly, to allow the solid tailings time to dry and consolidate enough to support a new level of the dam. These are suitable for facilities in areas of low rainfall and low seismic activity.
The centreline method is a hybrid of upstream and downstream designs. In Centreline construction, the dam is raised vertically from the starter dam. The dam crest therefore remains fixed relative to upstream and downstream directions as the dam is sequentially raised. This design method can also incorporate internal drainage to improve stability.
A single stage dam is built to full height in one stage with no further raises. This design is most commonly used for smaller tailings facilities.
Managing tailings storage facilities effectively
For the most part, tailings storage facilities have been historically well-managed with few incidents of failure; however, when they do fail, the consequences can be catastrophic for communities, local economies and the surrounding environment. Responsible tailings management requires companies to consider the management and governance of tailings storage facilities from their design, construction, operation through to closure. This should minimise the risk of catastrophic failures.
In this context, the objective of the Global Tailings Review is to develop an international standard for tailings storage facilities that addresses, but is not limited to:
- a global and transparent consequence-based tailings storage facility classification system with appropriate requirements for each level of classification.
- a system for credible, independent reviews of tailings storage facilities.
- requirements for emergency planning and preparedness.
The review will also consider governance options to ensure uptake of and compliance with the standard.
Beyond the international standard, the review may also make broader recommendations for industry, governments, international institutions and the investment community to secure the safe operation of tailings storage facilities.