About the Project
The Harrison River Bridge Pier 5 Timber Fender Renewal Project addressed significant deterioration to the timber fender system, which was an important piece to the bridge, as it served the purpose of protecting the central pier (supporting the center of the swing span) against vessel collision and/or debris.
00590 Harrison River Bridge is a turntable-style, movable bridge constructed in 1956. Located on Highway 7, 48km west of Hope, the two-lane, nine-span bridge is 314m in length. The swing span consists of two steel girders supported by a turntable on Pier 5. The pier is protected by a timber fender system which had reached the end of its service life due to significant section loss in the piles, upper caps, and bracing due to fungal decay.
Mott MacDonald led the detailed condition inspection, options evaluation, detailed design and contract preparation, and construction support services for renewal of the deteriorated timber fender. Construction was from August 2020 until November 2020.
Mott MacDonald oversaw a close-proximity inspection of the fender’s timber piles, caps, sheathing and bracing elements. This included above-water visual inspection and drilling of the perimeter timber piles. The objective was to confirm the depth of decay below the top of the pile to assess whether the fender could be rehabilitated or warranted a complete replacement. Anticipated vessel traffic and impact assessment, and the need for maintaining the protection, were considered during the initial scoping.
Four functional design options were discussed – one renewal and three replacement designs – including advantages/disadvantages, considerations for construction staging and public impact. An innovative approach involving removing deteriorated timber from the top down to a level of sound material and rebuilding above, allowed for retention of salvageable components.
Scope: Removal of the fender’s upper 2.5m and reconstruction with installation of 16 new timber piles, 515 lineal metres of 305mm x 305mm caps and verticals, 425 lineal metres of 203/102mm x 254mm bracing, and 1200 lineal metres of 102mm x 305mm sheathing. A steel upper platform (4.5 tonnes) and access ladder extension improved maintenance access to the swing mechanism.
Mott MacDonald used a robust project approach focused on safety and quality, innovation, and schedule/budget adherence. Highlights include:
Innovations: Inspection efforts identified salvageable timber piles and at which elevation sound timber could be anticipated. New timber connections were detailed to nearly eliminate holes in the top of members which provide vulnerability for premature deterioration. Incorporating the steel pipe extensions on the nose piles eliminate the need for additional piling and more complicated connections.
Schedule / Budget: The project team worked to understand and better define perceived Contractor risks/uncertainties. This allowed the necessary time to finalize environmental permits and better define necessary mitigation measures for the instream works; improve the construction schedule length and flexibility; remove scope that required very low water levels; and, reduce permanent access requirements. The project attracted strong Contractor turnout and resulted in Contract award at approximately 85% of the revised Engineers Estimate.
The Harrison River Bridge is a successful example of innovation and collaboration among Mott MacDonald, the Ministry, and other consultants and stakeholders, to cost-effectively preserve and extend the life of an important infrastructure asset through renewal instead of replacement. The approach reduced environmental and user impacts, representing a preservation mindset for future, as infrastructure assets age in tandem with increased Indigenous, environmental, economic, and social expectations.