After more than 20 years of discussion, a major Australian bypass is set to open ahead of schedule

The construction of a new motorway-standard road that will reduce travelling time between New South Wales and Queensland, Australia, to five minutes seems like a straightforward project.

However, when construction works are adjacent to an operating airport, the alignment includes three government jurisdictions with different development and environmental legislation to be satisfied and there are sensitive environmental issues to be addressed, the $A543 million (US$471.6 million) Tugun Bypass project was always destined to be a challenge.

PacificLink Alliance, which comprises Queensland Main Roads, Abigroup Contractors and SMEC Australia, was appointed in February 2006 by the Queensland Government to design and construct the bypass. It will provide a high-speed link between the popular Gold Coast resorts in south-east Queensland on Australia''s eastern seaboard to northern New South Wales, separating interstate vehicles from local traffic.

The Queensland Government has committed $A423 (US$376.45 million) million of the total project cost with the Australian Government contributing the remainder.

The project includes construction of 7km of dual carriageway; a 334m tunnel underneath the Gold Coast Airport''s runway extension; five bridges including three overbridges and twin bridges across a valley; 800,000m3 of earthworks; 160,000m3 of concrete and 90,000tonnes of asphalt. An intelligent transport system (ITS) for traffic, plant and communication systems is also being developed.

PacificLink Alliance has taken construction and the associated challenges all in its stride since works started in June 2006, and the project is now set for a mid-2008 opening, six months ahead of schedule.

Bulk earthworks for the project are complete, the five bridges will be completed by December 2007 and mechanical and electrical installations for the ITS is powering ahead. Although works for the tunnel have been ongoing since construction started, the 334m tunnel has proven to be the most challenging aspect of the Tugun Bypass, and will continue to be challenging until the project''s completion.

Initially, the project''s focus was the completion of the essential tunnel works (ETW) by the 10 November 2006, which was an agreed deadline between Queensland Main Roads and Gold Coast Airport Limited. The 334m tunnel traverses underneath the airport''s runway extension: however the runway works could not commence until the ETW was completed. The ETW, which included construction of the diaphragm walls, central barrettes and tunnel roof, was completed 3.5 days ahead of schedule and the Gold Coast Airport runway extension has since been completed and is operational.

The tunnel is being built within an area that has a water table near the natural surface level. Before excavation of the tunnel could commence, a detwatering system was installed that would lower and maintain the water table level up to 12m depth for 900m, the length of the tunnel and tunnel ramps.


Tugun Bypass tunnel and airport runway extension nearing completion in April 2007

The dewatering system included the construction of 21 dewatering wells, 11 wells in the tunnel and five at each of the northbound and southbound ramps. Two water treatment plants have also been constructed on site and 44 re-injection wells along the eastern and western side of the tunnel and approach ramps maintain the natural groundwater levels in surrounding areas.

With the ETW completed, the next focus was the tunnel excavation that took five and a half weeks and included 60,000m³ of sand. Excavation was a slow process because removal of material had to be balanced both vertically and horizontally in each tube to ensure that differential loading on the tunnel structure was minimised.

Each tube of the tunnel is 6.1m deep and 13m wide to accommodate a possible future conversion from a four to six-lane facility. The tunnel roof is 2m below ground level, the underside of the tunnel floor is 11m below ground level and therefore controlling the groundwater flow while maintaining production was challenging. Water control continues to be a challenge for the project and despite the team''s continuous improvement in dealing with the treatment of recharge groundwater, water control will remain a constant challenge throughout the project.


Waterproofing the screw piles

When the tunnel is complete and the dewatering system is turned off, the water table will return to its previous level and place the tunnel slabs under uplift loads from the water pressure underneath them. In simple terms, the tunnel will become like an air-filled ball in water that will want to float.

Screwpiles have been inserted to act as tension piles, effectively ''anchoring'' the tunnel ramps to prevent them from floating. This has included the installation of 2,200 screwpiles, varying in length from 6- 30m. They were installed by high torque driving units with capacities of 120,000Nm and 200,000Nm respectively, mounted on a 30tonne excavator and a 45tonne excavator.

The construction of the tunnel ramps and base slabs is done in ''lots'' or individual concrete pours. There are 46 tunnel ramp lots in the northern tunnel ramp, which are 10 x 15m in size on average. Thirty-six tunnel ramp lots make up the southern tunnel ramp and are an average size of 20 x 20m.

The base slab consists of 27 lots within the tunnel portals at an average size of 26 x 15m x 1.2m deep.  After excavation, including in between the sheet piles installed for the tunnel ramps, blinding concrete was cast to shape and then joint waterproofing and sheet membrane was installed in readiness for reinforcement. In the ramps, screwpiles are installed before blinding is cast. Reinforcement is connected to the diaphragm walls using friction-welded couplers. Each base slab is approximately 450m3 per lot.

Also included in the slabs is provision for cathodic protection, drainage pipes, conduits for services and associated pits. The cathodic protection for the Tugun Bypass tunnel walls and barrettes uses a soil anode impressed current cathodic protection (ICCP) system. This will provide protection to the steel reinforcement embedded in the concrete and is innovative in the terms of the system and scale of application. The ICCP system will be monitored using remote monitoring control units.

By September 2007, the tunnel base slab was completed and the tunnel ramp slabs nearing 90% completion. Remaining work on the tunnel and ramps includes construction of the tunnel ramp walls, architectural linings, steel canopy stadium structures at both portals, asphalt and the mechanical and electrical services. The mechanical and electrical requirements for the tunnel involve automatically controlled multi-stage lighting, a deluge system including secured water supply for fire-fighting purposes, traffic management and motorist and emergency services communication.

A high voltage power supply from two sub-stations is provided for the tunnel to power the lighting, ventilation/smoke management systems and fire services, with redundancy provisions to safeguard against a possible outage of one incoming supply.

Intelligent transport systems and closed circuit television cameras control and monitor the motorway and tunnel traffic, which are linked to traffic management centres in Queensland and New South Wales.
A full water deluge system will be installed. The water supply is capable of over two hours continuous supply at 240litres/sec with two storage tanks holding 1 million litres of water each.

To ensure adequate ventilation in the tunnel, each tube will contain nine jet fans that are 1,250mm in diameter. When the tunnel operates normally, these jet fans are unlikely to be used as the tubes are self-ventilated by the ''piston effects'' of vehicles entering and exiting the tunnel.

During peak congestion, only two of the nine fans in each tube will operate to fulfil air quality standards. In the event of a fire, at least six jet fans in the incident tube are required to operate in an emergency with the assumption that three fans are inoperative as the result of the fire incident. On completion, the tunnel will undergo rigorous safety and reliability testing before the motorway is opened to traffic.

It has been a long road for the Tugun Bypass to now be nearing its opening.

Discussions about constructing a Tugun Bypass have been ongoing in the local Tugun community for over 20 years. The official design and environmental impact studies commenced in 1998 and after various amendments, final approval for the project was received in February 2006. For the thousands of commuters and the local community that are affected by the daily Tugun gridlock, in less than a year the highly anticipated bypass will finally be a reality ·