Since 1969, Klohn Crippen Berger (KCB) and its predecessors have provided geotechnical, hydrological and hydrogeological services for the large copper-molybdenum mining complex located near Logan Lake, British Columbia. The complex, now operating under the partnership of Highland Valley Copper (HVC) formed by Teck Cominco, BHP Billiton, and Highmont mining companies, is one of the world’s largest copper mining and milling operations with a daily milling rate of 136,000 tonnes.
KCB, in partnership with other consultants, has been involved in the design, construction and decommissioning of the mine’s tailings storage facilities including two Bethlehem, Highmont and Highland Valley tailings impoundments. The range of our services encompasses: investigation, design, construction monitoring and decommissioning of various tailings dams, including the implementation of permanent spillways.
The L-L Tailings Dam, presently 128 m-high, is a major earthdam constructed mainly of hydraulically placed cylconed sandfill. The dam is projected to reach the ultimate height of about 140 m in 2009 under the current mine plan. The L-L Dam together with the somewhat lower H-H Dam, constructed of earth – and rockfill further upstream, retain the 9.6 km-long, 2 km-wide Highland Valley tailings impoundment with a final storage capacity of 1.3 billion tonnes of tailings. Both dams are designed to high international standards for seismic and flood design criteria. The adoption of the modern centerline dam scheme with an impervious glacial till core and the use of compacted cycloned sandfill and waste rockfill for dam construction materials achieve the mine’s objective to provide safe yet economic permanent tailings retaining structures.
The unusually complex geological setting of the L-L Dam has provided continuous geotechnical challenges for the dam designers. The 43 m-high L-L Starter Dam was constructed in 1976-1977 over compressible lacustrine clay-silt deposits up to 12 m-thick in the valley bottom. Subsequent annual raises involved excavation of lacustrine deposits downstream of the Starter Dam and construction of a downstream buttress berm. The complex bedrock stratigraphy on the north valley slope, involving volcanic and sedimentary sequences, presents interesting foundation conditions in the form of high pore pressures and seepage as well as low shearing strength. The area has been extensively instrumented with piezometers and inclinometers. Seepage and stability control measures include: an upstream impervious blanket, downstream filter blanket and finger drains and buttress berms. Instrumentation results since 1990 has confirmed satisfactory performance of the dam foundation in the area.
KCB conducted a tailings run-out assessment for the L-L Dam in the Tailings Storage Facility. KCB identified valued components based on input from Teck, First Nations, the public and government agencies. KCB performed a tailings run-out assessment to determine the relative extent and distribution of tailings in the event of a dam failure and a preliminary assessment of the potential environmental effects.
- Site investigations
- Tailings run-out assessment
- Gap analysis
- Preliminary environmental effects assessment
- Construction monitoring