The November 2021 atmospheric river flood event in BC resulted in the washout of a bin-type retaining wall supporting the northbound (NB) lane of Highway 1 (Malahat corridor) on Vancouver Island. This required the closure of the NB lane, reducing the highway to single-lane alternating traffic during the day and full highway closures at night to accommodate emergency repair works to reinstate two-way traffic.

As this corridor supports an average of 25,000 vehicles per day, single-lane conditions caused traffic to back up for kilometres in each direction. In addition to being an emergency services route and major vehicle commuter route, the Malahat corridor is also the primary route for the transport of commercial goods between Victoria and the rest of Vancouver Island. During the days immediately following the washout, Victoria experienced a shortage of groceries and fuel – evidenced by empty shelves at supermarkets and gas stations running out of fuel.

To restore traffic flow along the Malahat and allow normal movement of goods/people between Victoria and the rest of Vancouver Island, the BC Ministry of Transportation and Infrastructure (MoTI) assembled a consultant project team consisting of McElhanney Ltd. (McElhanney) and Thurber Engineering Ltd. (Thurber), who were tasked with:

• Immediately assessing the site and making it safe to support single lane alternating traffic.
  
• Designing a temporary repair solution to reinstate two-way traffic, with a reduced speed limit.
  
• Design and construction of permanent wall replacement to reinstate two-way traffic to ambient design speeds.

Geographical challenges/constraints of the project site included steep mountainous terrain above and below the highway which terminate down at the environmentally and culturally important marine estuary of the Finlayson Arm at the mouth of the Goldstream River. In addition, the project site is located within the boundaries of Goldstream Provincial Park.

Thurber was on site the day of the washout event to assess the immediate danger to the highway and provide design recommendations to restore temporary traffic flow. Within 24 hours of the washout event, McElhanney attended the site and assessed the damaged wall for hazards.

Once single-lane traffic was restored, McElhanney and Thurber worked collaboratively with MoTI and their Maintenance Contractor, Emcon Services, to design and construct a temporary rock-anchored shotcrete wall to underpin the highway and temporary drainage improvements, which facilitated the restoration of two-way traffic within four days of the washout.

Once temporary traffic was restored, our priority shifted to designing and tendering the permanent wall under an accelerated timeline, which required intensive analysis and optimization with daily interaction between McElhanney, Thurber, and MoTI. We mobilized a geotechnical investigation, explored possible permanent wall solutions, conducted a multiple accounts evaluation of possible solutions, and completed an independent value-engineering workshop. Our solution, comprised rock-socketed steel pipe piles joined by a cast-in-place concrete wall with rock-bonded tie-back anchors, was tendered within four months of the washout with construction complete within two years of the washout improving climate and seismic resiliency.

McElhanney and Thurber achieved the following:

• Restored traffic flow and movement of goods/services under an expedited schedule
  
• Focus on safety—no recorded traffic incidents
  
• Practical/constructible design with five bids during a period of economic uncertainty in an extremely constrained site
  
• Design maintained two-way traffic through all stages of construction
  
• Resilient infrastructure addressing climate change and seismic risks
  
• Effective communication resulting in satisfied client