Duffs & Marlee Bridge Replacements

• Multi-site project
• Demolition and disposal of existing bridges, with Marlee Bridge being demolished in house by Delaney Civil
• Reclaiming sound timber in the demolition process, for reuse as part of the Council Sustainable Management Plan
• Identical designs for the bridges, with a variable-sized culvert span to cater to the difference in bridge length and hydrology requirements
• Permanently cased, large diameter bored piles penetrating three metres into the rock
• Prestressed concrete planks with transverse post tension bars
• Lifting in edge planks with scaffolding attached, providing instant protection from working at heights
• Trial assembly of precast planks prior to delivery onsite, preventing delays and additional costs during the closures
• Complex staging and intensive planning in the programming

Innovative bridge design solutions

To meet budgeting requirements, virtually identical designs were developed for the bridges, with a variable-sized culvert span to accommodate for the difference in bridge length and hydrology requirements.

Permanently cased, large diameter bored piles were used as they addressed potential scour concerns and eliminated the need to pile through the existing deck, improving safety and reducing the time spent working around traffic.

The new bridges used prestressed concrete planks with transverse post tension bars, which do not require an in-situ deck, meaning they were trafficable immediately and this reduced the closure time significantly.

The edge planks were also lifted in with scaffolding attached, providing instant protection for working at heights, and safe access to install the transverse bars.

A temporary steel support structure was also designed, so that it could be reused as an emergency bridge crossing or new bridge structure, providing future cost savings to Council as it is an emergency solution that can be implemented quickly in the event of flooding within the LGA.

Sustainable demolition of the timber truss bridges

Delaney Civil demolished Marlee bridge in house, under the safest identified methodology. The timber trestles for both bridges being carefully lowered and disassembled at ground level, significantly reducing the time spent working at heights.

Sound timbers were also reclaimed during the demolition process, as part of the Council Sustainable Management Plan.

Careful programming for project success

Effective programming was critical, with the bridge closures requiring complex staging, intensive planning, and contingency measures for plant, materials, personnel and weather. Each bridge replacement was completed in a 10-day closure period, minimising time in the waterway and reducing exposure to flooding risks.

Delaney Civil exceeded expectations by reopening Duffs Bridge on day seven and delivering Marlee Bridge within the 10-day closure.  To further reduce risk, Delaney Civil facilitated a trial assembly of the precast planks prior to delivery, ensuring efficient installation and minimising the potential for delays and additional costs during the closures.