Kaiata Water Supply

Isaac Construction were engaged to complete civil works for installation of 3 x 66KV cables between Prestons Substation to Belfast Substation which included trenching, construction of reinforced concrete base, shoring the sides of the trenches with timber, liaising with the electrical contractor for cable lay, backfill with thermal concrete, and reinstatement of trenches.

Project overview

Location Kaiata, West Coast, South Island

Scope $3.29M

Date of completion 2021

Isaac Construction were engaged to complete civil works for installation of 3 x 66KV cables between Prestons Substation to Belfast Substation which included trenching, construction of reinforced concrete base, shoring the sides of the trenches with timber, liaising with the electrical contractor for cable lay, backfill with thermal concrete, and reinstatement of trenches.

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Purpose

Isaac Construction were engaged to complete civil works for installation of 3 x 66KV cables between Prestons Substation to Belfast Substation which included trenching, construction of reinforced concrete base, shoring the sides of the trenches with timber, liaising with the electrical contractor for cable lay, backfill with thermal concrete, and reinstatement of trenches.

Overview

Isaac Construction has recently completed the installation of 6.5 kilometres of watermain and submain from Omoto to Kaiata, which is just inland of Greymouth on the West Coast. Residents within the Kaiata community have been reliant on low-pressure rainwater systems or ground water bores, which have questionable water quality, for several years. Delivering clean and safe drinking water is a project Isaac is proud to be part of.

A very tight deadline of 30 June (12-week programme) was set by Grey Council to meet a Provincial Growth funding requirement, and this was met by the project team. This practical completion time was a non-negotiable, with no EOT to be accepted and instant acceleration, all due to government funding for the pipeline. To meet this programme, mobilisation of teams and equipment began within only 7 days of the project being awarded. The main body of work required an average resource of 8 teams between pipe laying, road reinstatement, directional drilling, resurfacing and traffic management.

Upon arrival to the job site, it was discovered that an extra 400m of trenching would be required and it was still to be completed within the same specified timeframe. 100m of this trenching was outside the limit of works where we had originally thought the existing tie in was located. The new work of trenching over 100m outside the original starting line left us installing pipe through a known recurring slip zone where operators had to operate 14 ton excavators next to sensitive instrumentation installed to the ground to monitor the movement of the slip. The remainder of the extra trenching was an alignment change that required an entire new submain to be installed within Section 2 that wasn’t originally on the plans.

The project team encountered well over the allowance for wet weather days (10 days) and in this specification, rain was required to be over 10mm for a half day delay and over 21mm for a full day delay. Usually, it’s only 5mm and days after that 1mm to extend the programme. Amongst these conditions the local council had applied to NZTA for dispensation to complete sealing outside of the sealing season to complete works on State Highway 7. Not something that any contractor would readily agree to undertake, Isaac rose to the challenge to try and produce the best result that all parties could ask for. Trying to time operations for surface completion, and a weather window appropriate enough to begin sealing was extremely difficult. Ensuring air and surface temperatures were adequate leading up to the day of sealing, as well as afterwards to ensure proper embedment, was an undertaking like no other.

Challenges

Limited Workspace

Tight working spaces along the main atrial route in and out of Greymouth, on the true left of the Grey River, meant that traffic management and interactions with transport firms and the public were daily. Ensuring that trenching was done in an efficient manner to reduce the amount of material needing to be removed and replaced was key. Due to the large distance between traffic lights and the curving state highway a high level of communication was required to ensure school buses, oversized loads and general freight was able to make it through the work site safely. General duties had to be conducted with extra care and took much longer than it would normally take in some places, however patience and tireless pursuit to get the job right prevailed.

Unpredictable Weather and Ground Conditions

The variable nature of the weather on the west coast of the South Island made planning works difficult and conditions were not always ideal for trenching, pipe laying and reinstatement. Average rainfall for the west coast region can be 2000mm-3000mm annually. Our project was fortunate enough to have reasonably good weather for the better part, but when it did rain, it rained. The trenches could easily become creeks making all form of works extremely difficult. Because of tight deadlines it was not always practical to stop and so works continued through what west coasters would consider “light rain”.

The works through section 1 were a balancing act of good traffic management, appropriate storage, transport of pipe without damage, and a good weather app for predicting downpours. An original trench width of 700mm was used to try and reduce the amount of material that had to be removed for pipe installation, but it quickly became apparent that in some areas this would not be appropriate with limestone rocks up to 1.5m in size being removed. Where large machinery was unable to remove the rock, in some instances concrete saws, rippers and breaking heads were used to create passage for the pipework to be installed. While hard bedrock and boulders were an issue, there was also substrates which were extremely soft and would cause trench collapse and undermining if there was rain, care was taken to ensure trenches were supported wherever possible.

Testimonials

Joe Turner – Davis Ogilvie & Partners Ltd

Davis Ogilvie Greymouth recently worked with Isaac Construction in and Engineer to Contract and Engineers Representative role for a mutual client, in this case, the Grey District Council. The project was an extensive new watermain stretching several kilometres of State Highway from Greymouth, to the nearby township of Kaiata. Davis Ogilvie had been previously working with GDC to complete the design and feasibility of the project over a number of years.

The Project presented many complex challenges from a construction perspective. Due to the topographical constraints along the road alignment, space for new pipework was limited. Much of the new watermain was constructed within the carriageway. This presented a challenging work environment for Issac’s. Space was at a premium and much thought was needed to ensure delays on this popular commuter route/reginal service link were minimised.

Throughout the first few weeks of the program, many changes to the design alignment were made, all with the help of the knowledge and adaptability of the Isaac’s construction crews. Many of these changes resulted in a saving to the principal, and a reduction in public disruption, ultimately leading to a project delivered on time and on budget.

Weather in the area is also notoriously inclement, especially during the winter season when the works were being done. This provided further challenge, as with many crews travelling from away to work weekly on this project, large amounts of downtime were not an option. The team of Isaac’s project managers, and work crews did an excellent job of being adaptable at a range of tasks to ensure forward progress was made each and every day of the contract period.

We are happy to acknowledge that the expertise and experience of the Isaac’s team played an integral part in the successful delivery of this project. We hope to work with them on future projects, and look forward to seeing their team deliver other successful projects in the region.