On August 4, 2014, the tailings impoundment at Mount Polley Mine breached, resulting in the release of over 21 million cubic metres of water and mine tailings which flowed into Polley Lake, Hazeltine Creek and Quesnel Lake.
Klohn Crippen Berger (KCB) was retained by the Ministry of Energy and Mines (MEM) to support their inquiry into the breach. As part of this work, KCB undertook comprehensive forensic geotechnical investigations to assess the mechanism of the dam failure. This work included six months of field and laboratory studies followed by investigative analyses of the failure mechanism.
The results of KCB’s work provided the basis for understanding how the dam failed, and will also be an essential reference for the future design of tailings facilities in BC.
The field work included:
- Mapping of the failure area
- Seismic and resistivity geophysical surveys
- 24 sonic coring holes and undisturbed sampling
- In situ testing including SPT, CPT and vane shear
- Instrumentation: 22 piezometers to assess the water pressures in the foundation soils and 5 inclinometers which were able to record post-failure creep movements along the sliding plane in the foundation.
The laboratory work was extensive and included:
- Over 1,000 basic soil index property tests
- Over 50 advanced soil strength and behaviour tests
These data were also provided to the Independent Expert Engineering Panel and used in their report issued January 30, 2015.
- Program planning and management
- Field Mapping
- Drilling, sampling and in situ testing
- Laboratory testing