A photogrammetry survey of a steep footwall slope at a mountain coal mine was conducted one day before a slab-type failure occurred. A second photogrammetry survey combined with a daily record of survey prism movements on the slope provided detailed information concerning the slope and the failure process. The paper demonstrates the variety of data that can be extracted from photogrammetry surveys and presents initial analyses of the factors contributing to the slab failures.
The Grande Cache Coal mine is located in the eastern slopes of the Rocky Mountains 23 km northwest of the town of Grande Cache in western Alberta (Fig. 1). This paper deals with a ground-based photogrammetry survey conducted immediately before and after a footwall slope failure in the No. 12S B2 pit, supplemented with movement histories of prisms placed on the slope. The slope failure consisted of two separate slab failures in a 40 m high footwall slope located in the western portion of the pit. The first failure occurred on June 30, 2006 and the second failure in the same area occurred one week later on July 7. At the time of the failure, the coal seams above the pit floor had been removed and the remaining slope had been bolted with 8 m long Dywidag rock bolts. Photographs covering the area that eventually failed were fortuitously taken on June 29 the day before the first slope failure and again on July 21 two weeks after the second failure. Images taken before the slope failed recorded the position of up to 22 active survey prisms while those taken after the failure captured up to 14 active prisms; eight prisms were lost because of the slope failure.