Response to Movement Within an Open-Cut Rock Face: Case Study from Ottawa Light Rail Project, Ontario, Canada

The Kiewit Eurovia Vinci (KEV) Partnership are currently designing and building the Ottawa Stage 2 LRT Project. The project includes a new 27 km LRT extension of the Confederation Line and includes 3.4 km of cut and cover tunnels and significant highway widening and structures scope. Brierley Associates supported KEV by providing temporary support of excavation system designs for various segments of the open-cut trench excavation through soils and rock. The rock along the project alignment consisted of layered limestone, dolostones and shale beds with predominantly subvertical and subhorizontal jointing. Based on the site investigation top of rock data, it was assumed that several faults would cross the alignment although they were not mapped. Given the rock mass conditions within the project area, a spot bolting rock support system was implemented for the vertical rock cuts in combination with regular rock face mapping and monitoring. Along one segment of the alignment, a large sub-vertical fault was exposed below the installed soldier pile and lagging shoring. During excavation, rock conditions and monitoring data indicated a potential rock slope instability in the vicinity of the fault along one wall of the excavation. The survey, engineering and contractor teams responses were coordinated to mitigate the risks to the project and personnel. Sequence of events, response successes and lessons learned are presented.