Ten Mile Slide Stabilization

Ten Mile Slide is a 1 M m3 landslide in soil near Lillooet, BC, that has affected Highway 99 and a CN railway line for over 25 years, resulting in single-lane traffic and frequent maintenance of the highway surface. BGC was engaged by the BC Ministry of Transportation and Infrastructure to investigate and interpret the slide mechanism and to complete a detailed design, tendering, and construction engineering review of stabilization measures. BGC was the lead engineering consultant for the stabilization of the landslide using structural reinforcing with sub-consultants GEA Engineering (structural) and Urban Systems Ltd. (highway design). BGC completed geotechnical site investigations, instrumentation installations, and interpretation of slide movement. BGC provided change detection analysis for the landslide using MoTI Airborne Laser Scan (ALS) data from 2009 to 2017. BGC also provided Terrestrial Laser Scanning (TLS) with change detection commencing in 2017 and throughout construction. Ongoing geotechnical monitoring includes real-time monitoring of vibrating wire piezometers and load cells on selected ground anchors and quarterly slope inclinometer readings. BGC developed and deployed Augmented Reality (AR) scenes of slide movement and the completed stabilization measures at First Nations community consultation events using Microsoft’s HoloLens AR device and Clirio’s ADA platform.

The work included slide stabilization and highway re-alignment and incorporates approximately 275, 2.5-metre square concrete anchor blocks with post-tensioned 30 m long 66 mm diameter 1035 MPa (150 ksi) double corrosion-protected threadbar soil anchors above the highway. A tied-back concrete tangent pile wall comprising 150 x 1.5 m diameter drilled reinforced concrete shafts with an integral concrete cap beam retaining wall and guard rail along the outer edge of the highway. The anchor loads are monitored using vibrating wire load cells with real-time data acquisition, upload, data reduction, and plotting. This significant slide stabilization project resulted in the return of a properly graded and paved highway with a 60 km/h speed limit through the slide area and removes this long-term transportation bottleneck for the people of Lillooet and the Xaxli’p First Nation.