Posted by NRSBU on 11 August 2011
Currently, March Construction, pipeline subcontractor to Downers Ltd, have installed approximately 650m of both the 800mm dia and 250mm dia HDPE pipelines. They have started at the Bells Island end and are working towards Saxton Island and will then move towards Monaco. March are presently working in the inter-tidal area north west of Saxton Island and excavating the trench during periods of low tide.
March Construction have been liaising with the Iwi monitors directly with respect to the day to day programme of works and keep them informed as to when excavations of the foreshore area are to be carried out, and this has been working well.
Progress to date has been slower than expected. The trenching is taking longer as fine silt and sediments often flow back into the excavation before the pipe can be installed. This means the trench needs to be re-excavated several times to ensure the pipe invert is at the correct depth and at an appropriate grade. The weather has also impacted on progress with wind in particular causing issues. March Construction has advised wind speeds for the period 1st May to 11th July to be demonstrably higher than normal. In addition, the February earthquake in Christchurch meant delays in getting staff and equipment on site initially.
Installation of the bedding material has also proved challenging for the contractor as more material than initially thought is needed to compensate for the extra excavation that is required. The bedding material is an important component of the pipeline as it provides protection for the pipe from larger stones being placed against it as well as supporting the pipe when the backfill is placed. March Construction intends to start transporting bedding material across to Saxton Island via a barge being loaded at Monaco boat ramp this week. This bedding is for the section of trench currently being excavated and additional stockpiles will be made on Saxton Island for that section of pipeline.
Quality is also a focus for both ourselves and the contractor. There are two main areas that have been the subject of several discussions. The welding of the HDPE pipes. It is important this welding is done correctly to ensure integrity of the pipeline. We are confident the procedures in place, record keeping and checking being done mean the welding is of a high standard. Also concentrated on is the depth and gradient of the pipe, with a particular focus on ensuring the pipe gradient is appropriate, that is with no unintended high or low spots. March are using GPS technology on their excavators to confirm the depth and alignment is as per design, divers to check trench condition before laying the pipe and an independent survey firm to confirm the as built location.
In the coming weeks, March will be installing pipes up to and along Saxton Island. This will present its own challenges as all access for personal, plant and materials, is via boat or barge. On the positive side, this section of trench is less prone to impact from both tidal currents and wave action.
Project is on programme for completion by December at a revised cost of just under $13mil.
The regional pump stations at Beach Road and Saxton Road are being upgraded as part of the Regional Pipeline Upgrade project. The work is progressing well and both pump station are expected to be operational in October 2011.