Scope of Works
Telstra engaged UEA to construct a new underground access chamber/manhole, and to bore a new telecommunications conduit from Floreat Beach, 800 metres west/northwest to the seabed. The new conduit has been used to connect to the underwater cable. Telstra obtained approval from the Western Australian Planning Commission for this cable landing infrastructure development, with the work carried out in accordance with the approved Environmental Management Plan developed by UEA.
In order to undertake this work, UEA completed the following activities:
Established a site compound and drill site
Installed security fencing around the site compound
Horizontal directionally drilled 800 metres of seawall to predetermined coordinate
Installed completion piece and buoy on the seafloor using a dive team
Constructed an underground steel reinforced concrete access chamber/manhole
Restored the site in accordance with Town of Cambridge standards
Using an in-house design team, UEA undertook the initial surveying for the HDD design and beach manhole design. By using a Trimble GPS system, UEA was able to accurately design the new submarine cable conduit in line with the capabilities of the HDD rig. Using this data, a wireline system was employed to track the drill head from the beach out to the predetermined coordinates on the seafloor. Upon completion, additional data (coordinates and levels) was collected along the installed conduit for the finalisation of the work as executed drawings to be provided as part of the final quality assurance report.
During the operation, the drilling fluid was constantly monitored to ensure that no loss occurred, with both xanthan gum and freshwater used near the drill exit point to protect marine life. Once the drilling was complete, UEA engaged divers to recover the drill head from the seabed. The divers pulled a rope through the drill rods and installed a subsurface buoy, and the drill rods were left in-situ to act as the conduit for the optic fibre cable. UEA constructed a concrete access chamber around the new conduit, and with the final restoration of the site to complete the project.
Challenges and Completion
The sandy ground conditions made it difficult to mobilise and setup the equipment. In order to manage the soft ground, a 100 tonne crane was utilised during both mobilisation and demobilisation to assist with the loading and unloading of the HDD equipment. Heavy duty track mats were utilised to provide access to site for vehicles, and steel casing was installed from the entry point to the limestone as part of the HDD. This was a total of thirty metres of casing through the sandy ground to limestone in order to eliminate the risk of borehole subsidence.
Rough seas during the project made it difficult for the divers to work on the seafloor. The swell was high, and coupled with relatively shallow water depth, making it difficult for the divers to remain steady with visibility poor at the HDD exit location.
Even given these challenges, the project was completed successfully with an overall duration of four weeks.