Bribie Island Bridge - Pedestrian underpass construction

Project background

The Bribie Island Bridge pedestrian underpass is a shared user path that provides a pedestrian link under the bridge between Sylvan Beach Esplanade and Welsby Parade Bongaree.

The underpass was built approximately 30 years ago and consists of a 2.6m wide footpath with up to 2.5m high retaining walls either side at the lowest point under the bridge structure.

The underpass has always been highly utilised by the local community and is the only safe pedestrian point of crossing the bridge within this area of the island.

In February 2019, TC Oma approached the coastline of South East Queensland. The category 2 cyclone at the time came within 500km of the coast line with gale force winds of over 100km/hr. This, coupled with the king tides experienced at the time, resulted in damage being sustained to approximately 15m of the underpass retaining wall on the Pumicestone Passage side.

Design works on a full reconstruction of the underpass commenced in March 2019 with construction works commencing in April 2019. Completion of the construction works occurred in December 2019.

Project challenges

Critical Services Infrastructure

During the design stage it was noted that critical Unitywater services, in particular, high-pressure sewer line and high-pressure water main that service the island, were being supported by the existing underpass retaining walls. The design called for the Construction team to keep in place a section of existing wall which then required extensive anchoring prior to commencement of the new underpass.

Ground Water

As the main construction works commenced, once the existing retaining wall was anchored, an issue arose with the level of the ground water at the lowest point directly under the Bribie Island Bridge.

Drainage Pit Installation

A new drainage pit was installed as part of the overall renewal project.  Issues arose with the location of the pit with old redundant services and unknown mass concrete footings discovered during excavation.  This resulted in a greater depth required for the pit which then needed shoring and sheet piling for it to be constructed.

Pedestrian Management

The underpass provides a safe route of travel for pedestrians/cyclists travelling between Welsby Parade and Sylvan Beach Esplanade. This section of roadway is extremely busy and there is no alternative safe route of travel for pedestrians in this area. It was decided in early March 2019 to put in place pedestrian management to ensure the safety of all pedestrians attempting to cross at this point during the renewal of the underpass.

Project costs

These costs are as at project completion.

Design $20,000.00
Pedestrian management $562,839.67
Construction works $996,023.00
Total project cost $1,578,862.67


Bribie Island Bridge - Eastern side, Bribie Island Road, Bongaree 4511  View map

Google Map