From the magazine, HDD, Rehabilitation, Tunnelling

SADB: on time and on budget

Basslink Interconnector Project – Tasmania

SADB were contracted by Italian giant, Pirelli Cavi e Sistemi Energia SpA, to complete civil and directional drilling works on the Basslink Interconnector Project at Four Mile Bay in Georgetown, Tasmania. The site is regarded as a highly environmentally sensitive area on Aboriginal Heritage land.

As part of the project SADB constructed a 2 km access track from the road entrance point to the drill site and surrounding access areas, which included the supply and installation of box culverts under an existing creek and open drain. The tracks installed had to be suitable to carry all plant and equipment to and from site. Additional works were also completed on the foreshore area to ensure minimal disturbance to the beach area.

The directional drilling work completed included the supply and installation of two drills under the existing sand hills opposite the shore. These sand hills were treated with particular care due to the environmental concerns. SADB completed two drills under the sand hills ranging from 4 to 13 m in depth. Both drills were 145 m in length and 8 m apart.

The first drill was completed in three days in which 160 and 315 mm conduits were installed in the same hole. Two passes were completed to upsize the pilot hole to a 700 mm diameter hole. The reamed hole was oversized due to the clay/sand conditions. The second drill was completed in four days in which a 400 mm conduit was installed. Again, two passes were completed and the hole was upsized to 700 mm diameter. The project was completed on time and to the satisfaction of the client.

SA Water Sewer Project – Stirling South Australia

SADB were contracted to supply and install a new sewerage system in a highly sensitive environmental area of the Adelaide Hills. The majority of the project was constructed in the rear yards of existing properties with immaculate gardens. The major problem encountered on the project was the lack of access for the installation of the 180 mm gravity sewerage system and the residents’ concern regarding the use of heavy machinery in their properties.

As part of the project SADB undertook an extensive customer consultation program. The project manager outlined a step by step construction program with residents to clearly explain how they and their property would be affected during construction. A full dilapidation report was completed with each resident which was signed off by residents and the SADB project manager.

The project included the supply and installation of 1003 m of 180 mm HDPE conduit, to grade. For 70 per cent of the project, directional drilling was used while the remaining mains were installed by conventional methods. The challenge faced was the drilling of the lines in the rear yards with minimal grades, ranging from 0.5 per cent to 2 per cent. Additional time was taken to ensure that each drill was completed to the design specifications and on average 30 m of drilling was completed each day.

The varying ground conditions from dry areas to well watered gardens provided another obstacle for SADB to overcome. Other tasks completed as part of the project included 35 house connections, and installation of 15 manholes and connections to the existing SA Water infrastructure.

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