Rockfill Compaction Trial

Siavash Farhangi, David Ritchie, Narendra S. Verma

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Mining Geotechnics

ABSTRACT: ompaction Trial Siavash Farhangi, David Ritchie & Narendra S. Verma AMEC Environment & Infrastructure, Mississauga, Ontario, Canada ABSTRACT Rockfill, a frequently used material in construction of mining and hydro-electric dams, is difficult to compact and is therefore susceptible to excessive compression and settlement relative to other zones constituting the dams. The post-construction settlements can lead to differential settlement and deformation of the adjacent zones and cause stress concentration, arching and cracking of low permeability cores or membranes. To minimize deformations, rockfills are traditionally compacted by vibratory smooth drum rollers. In recent years, many practitioners have utilized haul trucks, which provide higher loads to compact rockfills. A compaction trial was carried out to examine the efficiency of loaded mine haul trucks in compacting rockfills with various lift thicknesses, in which settlement and density measurements were used to compare the compaction efforts of a smooth drum compactor to loaded mine trucks. RÉSUMÉ Le matériau d'enrochement, utilisé fréquemment dans la construction des barrages miniers et de barrages hydro-électriques, est difficile à compacter et est donc susceptible de compression excessive et d'affaissement par rapport à d'autres zones constituant les barrages. Les affaissements post-construction peuvent conduire à un affaissement différentiel et à la déformation des zones adjacentes et peuvent provoquer la concentration des contraintes, des voûtes et des fissures des noyaux ou membranes de faible perméabilité. Afin de minimiser les déformations, les enrochements sont traditionnellement compactés par rouleaux vibrants de cylindre lisse. Au cours des dernières années, de nombreux professionnels ont utilisé des camions de transport, qui fournissent des charges plus élevées pour compacter l'enrochement. Un essai de compactage a été effectué pour examiner l'efficacité des camions miniers chargés pour compacter l'enrochement en chargements de différentes épaisseurs, dans lequel les mesures d'affaissement et de densité ont été utilisés pour comparer les efforts de compactage d'un compacteur à cylindre lisse avec des camions miniers chargés. 1 INTRODUCTION Detour Gold Corporation operates the Detour Lake Mine located north of Cochrane, Ontario. Tailings slurry is deposited from pipelines located on the crest of the tailings impoundment dams. The dams comprise a rockfill embankment with an upstream low permeability till facing. The majority of the rockfill used in the construction of the dams is run-of-mine waste rock, which to date has been dumped, spread in maximum 1.5 m thick lifts and compacted with minimum six passes of a 10 tonne smooth drum vibratory compactor. To simplify and enhance the effectiveness and economics of construction, a field trial was carried out to assess the possibility of using loaded mining trucks (CAT795 with loaded weight of 510 tonnes) for compacting the rockfill in thicker lifts. 2 BACKGROUND The 10 or 15-tonne roller compacted rockfill is significantly more compressible than other fill zones comprising compacted till, sand and gravel or crushed stone. Furthermore, whereas much of the rockfill compression occurs during construction, the zone located upstream of the low permeability core experiences additional deformations on inundation (Paré et al, 1984, Verma et al, 1985). The core and granular filter zones supported on rockfill are therefore susceptible to undesirable differential settlement, lateral deformations, arching and stress concentrations when located over or adjacent the rockfill zones. Therefore, reducing the magnitude of rockfill settlement is important in the construction of rockfill dams. This transition from loosely dumped to compacted rockfill in dam construction occurred during the period of 1955-1965 due to excessive compressibility, segregation and post-construction volume changes observed in pre-1950's embankment/dams (Cooke, 1990). Experience has shown that rockfill material placed in thin layers and compacted by vibratory roller from a more stable mass in which settlements are minimal (USBR, 1987). Effectiveness of conventional vibratory rollers for lifts greater than 0.5 m thick is however questionable. The optimum loose rockfill lift thickness is generally about 1.0 to 1.5 m for medium to hard rocks, with the maximum rock size limited to two thirds of the lift thickness. Larger rock sizes are often incorporated into the fill provided that the rocks do not protrude above the fill surface and hinder compaction. The most commonly used compaction method for rockfill utilizes vibratory smooth-drum rollers with vibration in the range of 1200 to 1500 vpm and speed of 2 mph (3.2 km/hr) and a minimum static drum weight of 8 tons (7.2 tonnes) that exert a minimum operating dynamic force of 15 tons (13.6 tonnes). Generally 4 to 6 roller passes are employed, as more passes tend to crush and pulverize rock at surface without adding significant compaction to lower part of the lift (Breitenbach, 1993). Adding compaction water (sluicing) reduces the segregation and allows higher densities to be achieved by softening the fines and/or facilitating inter-particle sliding

RÉSUMÉ: ill Compaction Trial Siavash Farhangi, David Ritchie & Narendra S. Verma

Access this article:
Canadian Geotechnical Society members can access to this article, along with all other Canadian Geotechnical Conference proceedings, in the Member Area. Conference proceedings are also available in many libraries.

Cite this article:
Siavash Farhangi; David Ritchie; Narendra S. Verma (2014) Rockfill Compaction Trial in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper308,author = Siavash Farhangi; David Ritchie; Narendra S. Verma,title = Rockfill Compaction Trial,year = 2014}