tailings dams and waste piles
In the mining industry, there has been a history of serious slope failures, many with multiple fatalities, involving the mines themselves and also surface structures built to handle waste products. The high rate and seriousness of these failures stem in part from the temporary nature of the parts of the system. The active mining face moves forward every day; waste piles grow; tailings dams are extended; haul roads are shifted; drainage is modified. Thus, although a mine might last for as long as 100 years, the components are inherently ephemeral, and consequently economic considerations discourage engineering these components for long-term stability.
In studying catastrophic failures in mining, there are two main areas of concern — the mine itself and engineered structures outside the mine meant to contain generated wastes. It is these external structures that pose the greatest hazard to the population living downstream from the mine and are the focus this website. Two principal types of waste from mining are waste rock - the unmineralized or poorly mineralized host to the ore - and tailings - ground up bits of ore from which the metals have been removed - and each is handled in separate facilities.
The likely modes of failure of tailings impoundments and waste piles have been known for some time. For example Casagrande and McIver (1971) provided an excellent overview. Strachan (2001) has recently analyzed the relative frequency of different sources of problems with both water and tailings impoundments and found for tailings this distribution:
| Cause | % |
Slope stability |
24 |
Earthquake |
17 |
Overtopping |
15 |
Foundation |
11 |
Seepage |
11 |
Structural |
8 |
Erosion |
3 |
Mine Subsidence |
1 |
Unknown |
10 |
None of these failure categories involve poorly understood processes. Instead they are caused by obvious mistakes or omissions in design, construction, or stewardship. The list above suggests that the disciplines of hydrology, geology, geotechnical engineering and mining engineering are all involved in preventing failures, so that effective communication among the practitioners of these disciplines is key to success.
The four large failures were chosen as examples of critical breakdown in communication for which extensive information on the geological and geotechnical conditions surrounding the failure are available. Each failure caused serious damage to property or the environment and three caused extensive loss of life. Also included is a speculative analysis of the Mufulira tailings inrush.
REFERENCES TO TAILINGS DAMS AND WASTE PILE FAILURES