ABSTRACT: Billions of tons of rock are shipped as overburden in surface mining operations annually worldwide. Some 40 million tons in China alone are dumped on waste piles which occupy large tracts of sometimes valuable land. Failures of these waste piles result in large scale environmental and other problems. This paper discusses the underlying mechanisms and gives some specific histories.
WASTE PILE FAILURE
The 220 m high spoil pile at the Janshah Iron mine, containing some 2.2 million cubic meters of waste rock, failed catastrophically in 1979. The resulting damage to the mine railroad disrupted production for more than six months.
Another serious waste pile failure occurred at the Shanbou Coal mine in West China in 1991. The soft foundation allowed the 20 million tons of waste rock to move downslope. Mine production was adversely affected for several months. Waste pile failures in southern China are nearly always related to heavy falls of rain. These result in what are termed mine debris flows or mudflows, arising from liquefaction and creep of waste
A wall of mud carrying with it boulders and rocks of all sizes, suddenly starts to flow. The flow which quickly widens out into a fan engulfs structures in its path, covering roads and fields until it slows and stops. The final shape of the deposit is a lobate form, with a steep terminal snout and margins. Debris flow containing 80-90% granular solids by weight, can move in sheets about 1 m or more thick over slopes with slopes as low as 5-10 degrees.
Other Chinese mines that have been impacted by debris flow from waste piles include the Hainan' Iron Ore mine, the Yonfou Nonferrous metal mine, and the Yonpin Copper mine. Millions of tons of waste rock together with large volumes of water and soil have been carried distances up to 7 km. The acid nature of the water resulted in fairly severe environmental pollution problems (table 1).
A summary description of the processes involved in pile slope failure (Johnson and Rodinc, 1984) is given below.