Westview Subdivision

Overview

Tarbotton Land & Civil was awarded the tender for Westview Subdivision in November 2021, working alongside the team at Davis Ogilvie. We were tasked with developing what was previously a berry orchard and green pastures into a residential subdivision with uninterrupted countryside and mountain vistas. From bulk earthworks, drainage, underground services to road construction and landscaping, we managed the entire process from start to finish.
The subdivision includes 38 new 4,000sqm+ sections and three existing dwellings located on Tinwald Westerfield Mayfield Road. Other features included six stormwater retention ponds, 33 soak pits, 30 culverts, 9 sealed right-of-ways and a 650m sealed road with swales on either side. This development was completed at the end of 2022.

Earthworks

Our team’s familiarity with the soil conditions in this area meant we knew it was important to ensure all topsoil and clay were removed before construction of any roads or right-of-ways took place; leaving it could result in the ground pumping which would cause damage to the road in the future. We used our CAT scrapers, fitted with GPS machine control, to make this a quick and efficient task. During removal, an additional layer of clay was found so we worked with Davis Ogive to remove this also. This allowed the roads to be constructed with a very solid foundation. All topsoil removed by the scrapers was stockpiled onsite and our Tarbotton quarry team processed this material into screened topsoil ready for landscaping.

Drainage

The stormwater system at Westview Subdivision consisted of six stormwater ponds, 1.5km of grass swales, 600m of subsoil drains, 33 soakpits and 30 culverts. All ponds, swales, soakpits and subsoil drains were constructed using excavators and graders fitted with GPS machine control so the team were able to ensure the design was executed with accuracy from the start. GPS control provides operators with a digital panel inside the machine with the final design and levels on it which responds to the position and elevation of the machines buckets/grader blades.
During this development, Mid Canterbury received a significant ‘once in x years’ rainfall event which put the drainage systems to the test. Ultimately they performed as expected and as a result of this rainfall, a decision was made to enhance the design by installing subsoil drains to provide even better drainage for similar sized rainfall events.

Sewer, water and underground services

This subdivision was one of the first developments in the Ashburton District to install a new low pressure sewer system. As this development didn't need the traditional gravity fed sewer laterals and mains, a pressurised system was installed instead. The low pressure sewer system means each lot requires a grinder pump/tank that, when required, pumps slurry into the pressurised system. Because transport of sewage is done under pressure, the pipe network is able to follow the contour of the land at shallow depth which provided significant cost savings to the client. We installed a pressurised pipeline 700m down the road to the nearest manhole where the waste entered the traditional gravity fed system.
In addition to the pressurised sewer system, we installed water mains from the nearest connection (700m away) and provided a connection to each lot. We also worked with EA Networks to install power and fibre throughout the development.
All sewer and water connections within the development were done using electrofusion joins. Tarbotton Land & Civil has our own electrofusion welder and a specially trained team who operate it. This method of connection meant there were zero leaks identified when testing the newly installed infrastructure.

Reading and right-of-ways

The main road into Westview Subdivision is a double lane chip sealed road 650m long with an asphalt cul-de-sac which provides access to nine chip sealed right-of-ways. The road construction included a subbase using AP65 and a base course of M4AP40. All aggregate was manufactured by our Tarbotton quarry located on Frasers Road. The road construction was made easy using a grader and skid steer both fitted with Leica GPS Machine Control. This technology meant our operators were able to construct the road very accurately and efficiently, ensuring the levels were done right. The roading surfaces were NDM tested followed by Benkelman beam testing to make sure the compaction and overall strength of the road structure was up to Ashburton District Council’s specifications.

Landscaping

The swales and stormwater ponds were finished using screened soil which was processed onsite repurposing material from the original site scrape. The soil was levelled using the skid steer and touched up by hand before sowing grass seed. The Tarbotton team excavated holes for the new trees to be planted and set up a temporary irrigation system to help encourage the grass and trees to establish. Grass strike in the swales and stormwater ponds was crucial to operation of the stormwater system onsite. We continued to monitor the grass until handover, which included frequent mowing.

Quality assurance

A big aspect of developing subdivisions is capturing data on all services being installed - both below and above ground - along with obtaining test results as evidence for quality assurance. At Tarbotton Land & Civil, we have an inhouse surveyor along with all the equipment required to make this as smooth and efficient as possible. Throughout this development, our team surveyed all surfaces, underground services, and compiled test reports as part of the project management. Working alongside Davis Ogilvie and the Ashburton District Council, we were able to provide detailed as-built drawings, photos and test reports for everything onsite, making the claims and final 223 application process smooth and efficient.