Work on the Southern Pipeline Harbour Crossing is entering its final stages, with the last phase of reaming now underway. The reaming work has involved gradually widening the hole beneath the harbour with increasingly bigger reamers. Widening with the 1.4m diameter reamer is now just over halfway complete.
The contractor has faced a number of challenges with work on the project, and initially expected to be in this phase of work about one month ago.
The drilling phase of the project was completed successfully in July – meeting a 750mm diameter target at Memorial Park from a distance of 1.6km, and maximum depth of 35m under the harbour from Matapihi side.
Once the drilling work was completed, the first phase of reaming work began. As the first reamer moved through under the harbour it encountered harder than expected material. This meant the reaming work progressed slower than expected and specialist machinery was required. In addition, the reamer encountered an obstruction as it moved through the hole from Memorial Park towards Matapihi. The obstruction has been removed and identified as a piece of totara wood that is approximately 51,000 years old. This is now in the care of the Tauranga Museum.
Steve Wiggill, Tauranga City Council Project Manager for the Southern Pipeline, says, “We’ve encountered a number of interesting challenges on this project, mostly due to the difficult working environment under the harbour. The contractor has experienced difficulties in reaming past the harder materials and obstructions such as the piece of timber.
"Specialist experts were brought in and additional equipment used, and this together with modifications to the machinery has enabled these challenges to be successfully overcome. Unfortunately, this has had an effect on the overall project timing, and we now expect a small amount of work will need to take place in January.”
There is no forecast change to the overall $99m Southern Pipeline project budget as a result of these challenges.
Once the reaming work is completed, a short period of between three-to-seven-days of 24-hour work is required to pull the pipes through from Memorial Park to Matapihi. This will be the last phase of construction work, and is still expected to be completed before the end of the year.
Once the pipes are pulled through under the harbour, there are two other smaller phases of work that will need to be finished before the Southern Pipeline project can be completed and commissioned. Pipes need to be laid at both ends of the Harbour Crossing, to connect it back to the Memorial Park pump station, and up Matapihi Road to the previously constructed section of the Southern Pipeline that connects to the Te Maunga Treatment Plant.
Both sites will then be cleared of all equipment and reinstated back to their original condition. The temporary reclamation at Matapihi will be removed. It is expected that this part of the work may extend into January 2018. No work will take place over the Christmas and New Year period.