Liquefaction flowslides in Rocky Mountain coal mine waste dumps

Abstract

Over the past 25 years there have been a large number of long runout flowslides from Rocky Mountain coal mine waste dumps. The waste dumps are constructed as end-dumped fills with an angle of repose of 38°. Dump heights range between 100 and 400 m. The dumps are normally founded on mountain slopes that are covered with a thin veneer of granular colluvial and dense stony till materials. Conventional stability analyses carried out for these dumps using friction angles equal to the angle of repose for the waste rock and typical values ranging from 30 to 32° for the foundation materials indicate that many should be stable. The flowslides occur rapidly and display surprisingly long runouts of up to 2 km in some cases. Detailed studies of three of these events indicate that static collapse of saturated or nearly saturated sandy gravel layers within the dumps may be responsible for the initial failure and the generation of high pore pressures which result in high runout mobility.Key words: mine waste dumps, flowslide, static liquefaction, collapse mechanics.

Field‐Scale Analysis of Flow Mechanisms in Highly Heterogeneous Mining Media

“…Heap Material Proper es Figure 3 shows the particle size distribution for seven samples collected from the fi nal lift. Th e median (d 50 ) grain size ranged from ?5 to 10 mm and suggests that the porous medium would be more appropriately classifi ed as "matrix supported" using the classifi cation of Dawson and Morgenstern (1995). Visual observations also showed areas of clast-supported zones near the surface, and are consistent with a biased particle size sampling.…”

Field‐scale experiments of unsaturated flow and solute transport in a heterogeneous porous medium

“…Additional details of the construction of the CPE and the internal structure of mine waste rock piles are given by Nichol et al [2000Nichol et al [ , 2003c. The grain size distribution of the waste rock in the CPE (Figure 2) suggests that it falls close to the boundary between a system that can be characterized as matrixsupported and one that is clast-supported [Dawson and Morgenstern, 1995]. Local regions that are matrix-supported and local regions with matrix-free cobbles and boulders were observed during construction.…”

Numerical modelling of the propagation of fast landslides using the finite element method

“…Among the large number of flowslides that have occurred due to liquefaction from the Rocky Mountains coal mine waste dumps, three interesting cases have been analysed in detail by Dawson et al [37]. Therefore, information on the characteristics of the flowslides, the properties of the involved materials, etc.…”

“…The flowslide could have rided over these layers of liquefied materials. The analysis of this flowslide is based on the geotechnical properties obtained by Dawson and coworkers [37], and accordingly it considers a density of 1900 kg/m 3 and an effective friction angle = 37 • . The mobilized mass has been taken from the data given in by [37] and the T v parameter has been chosen, from back analysis, equal to 68 s.…”

“…The two-dimensional model of Greenhills Cougar 7 dump is given in Figure 23. The terrain model has been obtained from the data given in Reference [37]. The results of the simulation are given in Figures 24-26, where it can be seen: (i) perspectives of the flowslide extension, (ii) isolines of debris depth and (iii) sections along vertical plane AA ( Figure 23).…”