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We are looking at the design of a Tailings Dam - also called a slimes dam, residue dam, or mine dump. It is proposed as 500 m diameter x 50 m high.
I have been told that Tailings Dams collapse at heights in excess of 30 m. The difference betwen an earth-fill dam, and a tailings dam is that earth-fill dams are designed to retain full depth of water, while tailings dams are huge settling ponds which are designed to silt up.
Does anyone have some guidelines on the design of high Tailings Dams?
Primary design professional would be a geotechnical engineer, at least in the US.
Practical maximum height of the structure will depend on many many items some of which are listed next:
- type of mine tailings (coal waste is not likely to support as high a dam as hard rock waste).
- foundation conditions
- earthquake ground motions
- downstream development
- environmental considerations and regulations
I’m sure there are many other ones that I missed.
Most times, at least in the US, tailings dams are sized to meet the anticipated needs of the mine for the next two to ten years (maybe longer if you have a really forward looking mine operator). The dam is used to sort the tailings and when it is about to get full, they start looking at how to expand the existing dam. As has been pointed out this can be done in many ways, however, the most common is either upstream or downstream construction. Both have advantages and disadvantages.
In the end design of tailings dams is very much like other dams, however, you generally have less control over the materials that will be placed within and as has been pointed out, quality control is sometimes not as tight as it could be.
Now back to your original question. It appears that you are looking at building a ring dam with a height of 50m. This would mean that H&H would have little to do with the dam. Therefore, a geotechnical (dam) engineer is what you would need. They should have worked with similar tailings in the past and preferably in the same geographic area as the proposed dam.
I would expect the biggest concerns to be (not in any specific order):
- foundation preparation beneath the 50m dam
- the ability of the dam material to relieve the pore pressure from the filling operation
- strength of both the dam and tailings materials
- earthquake induced ground motion
- rate of proposed filling
Future expansion of this type of dam would likely be by the downstream method, so siting of the structure would be key.