Combining traditional tunnelling technology with modern day rehabilitation techniques, ITS Pipetech recently provided a solution to the New South Wales Department of Roads & Maritime Services (RMS) to extend the life of an existing set of culverts that crossed the Princes Highway outside the University of Wollongong.
The prime objective of the work was to provide structural integrity and equalise the bores of a triple cell culvert that passed beneath one of the busiest arterial routes in Australia, and to achieve a design life of 100 years.
A secondary consideration was to devise a methodology and a sequence of works that caused the least disruption to the motorway, which carries over 18,000 vehicle movements a day just two metres above the top of the culverts.
The university culverts carry the Dallas Street branch of Fairy Creek, and this crosses under the motorway via a three cell precast concrete pipe. Over the years, as the Princes Highway had been upgraded and widened, the original 1,350mm triple culvert set had been extended to take additional traffic lanes. However, the northern extension was sized at 1,200mm, which, at times of heavy rainfall, was restricting the flow of water into the culverts. This would cause flooding to the upstream creek valley and threaten local property and the university campus.
The project had identified the probability of one or more of the culverts becoming blocked under a one-in-100-year storm event; therefore the feasibility review recommended that the pipes at the upper ends of the culvert set be enlarged to a common profile, similar to the remainder of the culvert. It was also recommended that a debris barrier with vehicle access be installed at the culvert entrance, so that maintenance and routine debris clearance could occur.
ITS Pipetech’s submission was to develop a methodology to tunnel around the existing inlet pipes, standardising the three cells into a common profile to meet the hydraulic demands, and reducing the potential for blockages and water retention in the upstream valley. Once this had been engineered, the void profile of the existing culverts had to be created and structurally lined together with the existing pipe to complete the structural rehabilitation process.
The proposal also took into consideration any potential damage to the riparian zone, and the effects that this would have in regards to damage to local flora and fauna. It also designed an access point from the motorway level to the culvert level, with an associated structural retaining wall.
It had been identified that any blockage of the culvert would result in significant flooding to the surrounding area during periods of high intensity rainfall, with the possibility of an eventual collapse of the culvert. This would risk the security of the motorway above, causing possible closure and widespread traffic chaos. This section of motorway is a fundamental link between the Port Kembla industrial area and the Hume Highway, with average annual daily traffic of approximately 18,000 vehicles (16 per cent of which is heavy goods). Closure of this stretch of motorway would have had serious ramifications on the local economy, as well as resulting in negative exposure for the client.
The brief was to remove the restrictions in the head pipe, create a structural element to provide a 1,350mm void, and then to reline this with a fully structural element – providing the required diameter and negating the need for extra works to maintain capacity and avoid road closures.
ITS Pipetech’s proposal was to remove the initial 6.5m of 1,200mm internal diameter concrete pipework to each of the three cells, and replace them with a cast in situ reinforced structural pipe bore. Matching the existing diameter, it could be structurally relined with a UV-cured Berolina GRP liner to provide the client with an uninterrupted, free flowing three cell underpass to meet hydraulic requirements.
The initial 6.5m of each culvert progressed from a headwall intake under the breakdown lane and inside carriageway of the northbound lanes of the Princes Highway, one of the busiest traffic highways in Australia.
The contract scope preference was to avoid any closure of the highway. In order to remove the pipes without disruption to the traffic, ITS Pipetech proposed a modified tunnelling system using a three-stage heading arrangement commencing with the outer right, then the outer left, before completing the middle bore.
As the heading advanced, the existing concrete pipe could be broken up and removed, leaving a space large enough to facilitate casting a structurally reinforced surround, to form a bore at a diameter similar to the existing downstream pipework.
Prior to this, ITS Pipetech had to construct an access to the site: a reinforced concrete driveway with a spray concrete retaining wall was built to allow plant movements to the tunnelling site.
The cover to the highway above was less than 1,600mm above the existing pipe, with allowance for working room to build the tunnel reducing it to 1,200mm. ITS Pipetech’s designs needed to accommodate SM1600 and 45 ton axle loadings.
ITS Pipetech opted for the use of Tunneline cast in situ structural lining system to construct the three bores, that were set at 1,350mm internal diameter to match the internal main cell diameters. Each bore was cast in a single operation using a 40Mpa structural concrete.
The final stage in the operation was to install a 1,350mm high strength UV-cured fibreglass Berolina lining through the culverts, to provide the client with a smooth bore structural lining with a design life of 75 years.
The adoption of old techniques and new technologies used in an innovative way enabled ITS Pipetech to undertake and complete the works efficiently, effectively and to the client’s specification. ITS Pipetech was able to deliver the project with zero accidents, zero incidents, zero lost time events, within program, with numerous benefits and at a significant all-round saving to the client and the community.
