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Tunneline extends culvert service life

After being awarded a VicRoads contract for the design and repair of two culverts underneath a busy highway in Victoria, ITS Pipetech specially designed Tunneline® liners to complete the job.

Situated to the southeast of Melbourne, Victoria, the Mornington Peninsula is best known as a popular tourist destination where beautiful beaches and calm waters are sheltered between Port Philip and Western Port. The peninsula is accessed via the M11 or Mornington Peninsula Freeway which features several sections of motorway and a standard trunk route between the suburbs of Frankston and Rosebud.

One section, between the Moorooduc and Nepean Highways, close to the town of Mount Martha, traverses two natural watercourses over the Devilbend and Tuerong Creeks. The watercourses drain a piece of land approximately 6,000 hectares in size. This includes the Moorooduc Estate winery, known for its Chardonnay and Pinot Noir grapes, and Devilbend Natural Features Reserve, a significant nature reserve with a large reservoir.

Both of the creeks flowed beneath the road and were culverted using corrugated steel plate units in 1993. The culvert at Devilbend Creek was 137 m long and constructed as a triple cell array with an inside diameter (ID) of 3,000 mm, while the Tuerong Creek culvert was a 120 m long triple cell, with an ID of 1,800 mm.

Both of the culverts had more than 4 m of ground cover. Over the preceding years they had both suffered from erosion, damage to the inverts, loss of plate thickness and some circular deformation to the side walls and obvert. Each culvert was beginning to show visible signs of rust and serious wear.

Towards the end of 2015, Victoria’s road traffic authority, VicRoads, identified the need for a structural rehabilitation to both culverts and opened tenders for a design and construction solution. The client stipulated that the solution should:

  • be fully structural and independent of the existing structures
  • have a design life of at least 100 years
  • conform with current Australian design standards

The client also stipulated that the rehabilitation works should not interrupt the passage of traffic above.

ITS PipeTech submitted a proposal for the project that focused on the use of a bespoke Tunneline® cast insitu reinforced concrete lining for both culverts. It was designed in line with AS 5100 and AS 3725 to comply with the client’s scope. The proposed final lining diameters for the culvert was 2,700 mm and 1,500 mm, respectively.

The final diameters conformed with the overall hydraulic requirements and a flow management proposal to undertake the works without having to restrict existing flows as the construction progressed. VicRoads awarded ITS Pipetech the works in February 2016 and construction commenced in late May.

Tunneline formwork being installed on site.

Tunneline, a high-strength concrete mix which is pumped into a bespoke formwork system, was specifically engineered by ITS PipeTech, in consultation with VicRoads, for the project. The design of the formwork was compliant with AS 3610, which specifies a bespoke high-yield steel reinforcement cage must cater for the load distribution, which was scoped as SM1600 with a B2 exposure classification for durability.

Tunneline works by creating an independent structural element inside the existing host structure that is able to take the full active and passive loading, without relying on the existing strength in the structure. Its design assumes the condition of the host is deteriorated and requires no additional treatment of the surrounding soils, regardless of voiding or loss of material.

Designing it to AS 5100 and AS 3725 results in a rigid structure, rather than a flexible lining, in line with AS 2566 Part 1 which states that flexibility is not required in design and that a life in excess of 100 years can still be assured.

The hydraulic efficiency of the final linings achieves a slight improvement against the existing structure due to the improved friction coefficient that is achieved with Tunneline. The elimination of joints in the lining allows for precise control of invert levels and the gradient can be achieved through the adjustable formwork system.

A significant factor in the project’s development was the management of existing flows and the preservation of the environment, neither of which could be affected by the works at any stage. However, it had to be balanced with the construction program as works progressed across the three separate cells on each of the crossings, with flows being diverted to whichever cell that was not being actively worked on at the time.

Lining production averaged 20 m per day in the 1,500 mm culverts and 10 m lined per day on the 2,700 mm pipe. As Tunneline is a one-pass system it required no pre-treatment, advanced grouting or post lining treatment.

Despite the onset of winter rains, which resulted in severe flooding to both sets of culverts, the lining works were successfully completed by the end of July. Project works totalled little more than two months.

The project design was in line with relevant standards to provide a 100-year life cycle, and was fully compliant with Australian codes and standards. The method successfully avoided disputations to the busy freeway above, and did not result in any lane or speed restrictions, accidents or road closures.

For more information visit the ITS PipeTech website.

This article was featured in the March 2017 edition of Trenchless Australasia. To view the magazine on your PC, Mac, tablet, or mobile device, click here.

If you have a project you would like featured in Trenchless Australasia contact Assistant Editor Nick Lovering at nlovering@gs-press.com.au

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