Costin Roe Consulting devised the civil engineering strategy to support a proposal by DEXUS to continue industrial development in a former quarry. The report authored by Costin Roe director, Mark Wilson B Eng (Civil) B Surv ME CPEng, would assist to facilitate completion of the original master plan for the site.
Greystanes Estate is a 156-hectare area within the SEL (Southern Employment Lands) precinct of western Sydney, positioned between the cities of Parramatta to the east, Blacktown to the north, Penrith to the west, and Liverpool to the south. The majority of the eastern portion of the SEL has been developed into a high-quality industrial and business park, valued by corporate occupants and employees for its proximity to public transport, cycleways, and the M4, M5, and M7 motorways – the Sydney CBD only 33 minutes’ drive away. Greystanes Estate has been publicly renamed “Quarry at Greystanes” since the first stages of development were completed.
About DEXUS and Greystanes Estate
DEXUS is one of the largest listed owners and managers of industrial properties in Australia. Known for working in partnership with their customers, and construction specialists, DEXUS’ mission is to deliver industry-benchmark property solutions tailored to the specific needs of manufacturing, logistics, and warehousing organisations. Existing DEXUS developments within Greystanes Estate include a distribution centre of 20,000 m² with associated office spaces of 1000 m² and 500 m², completed in 2012.
The 2016 proposal by DEXUS would represent the final parcel of land in the industrial precinct of the Estate to be developed – an area of 25.6-hectares on the western side referred to as “Lot 18” in documentation and called “Quarry West”. As the final stages (5 and 6) of the approved concept plan for the entire site, development approval for Lot 18 would bring to completion the rehabilitation and re-purposing of the large open-pit quarry which Greystanes Estate once was. The quarry had provided crushed rock and blue metal for road and building construction across Sydney.
Costin Roe Consulting appointed to provide civil engineering services
Costin Roe Consulting has been involved with previous developments at Greystanes Estate including industrial complexes for Solaris Paper and Symbion Health, and was commissioned by DEXUS to report on the civil engineering and storm-water management aspects associated with the proposed subdivision and development of Lot 18. Approval to proceed would eventually culminate in the construction of several large-scale industrial buildings and depend on successful completion of numerous subdivision and infrastructure requirements. Classified as a “major project” for approval with NSW Department Of Planning and Environment (DoPE), Lot 18 also needed to meet the engineering and planning requirements of both Holroyd City Council and Blacktown City Council, within the context of the approved Masterplan Strategy for the Greystanes SEL, the expansive area of Lot 18 straddling the two council jurisdictions.
“As civil engineers engaged in support for the development application, our objectives were to create a development site which respected the proposed architectural layout, responded to the topography and site constraints, and provided an appropriate and economical stormwater management system,” said Mark Wilson. “The development would need to incorporate best practice in water-sensitive urban design, consistent with the water quality requirements of both councils.”
The report and engineering design by Costin Roe Consulting would refer to earlier studies and reports made in relation to the whole Greystanes Estate site by engineering firms including PSM, PB, and GHD; the Landcom publication Managing Urban Stormwater, Soils and Construction (1998) – The Blue Book; the Institution of Engineers, Australia publication Australian Rainfall and Runoff (1988 Edition), Volumes 1 and 2 (AR&R), and the NSW Department of Environment and Conservation document Managing Urban Stormwater: Harvesting and Reuse.
Unique site history presenting uncommon challenges
Located on the eastern edge of Prospect Hill, extensive quarrying for approximately 100 years had left Lot 18 with an irregular, crater-like topography. Historically, as part of quarrying operations, several areas of the site had been filled in an uncontrolled manner using a variety of materials at depths of up to 32m. The western boundary of the development area is formed by the walls of the former quarry and these walls extend some 40-50m above the proposed developed site levels. One section of walling had partially collapsed due to a landslip that occurred decades ago.
From 2001, however, there had been controlled filling of the site at certain intervals, and of the four areas subjected to uncontrolled filling during the site’s long operational history, three areas were previously determined as suitable for industrial loading without additional working.
Effective, economical civil engineering strategies
Mark Wilson determined that an additional 500,000-600,000m³ of fill would be required to bring the land to proposed levels through earthworks to be undertaken by CWJ Civil on behalf of Boral Pty Ltd, operators of the former quarry now helping to facilitate easier development by DEXUS, with roughly half of this requirement able to be met through the redistribution of suitable fill available on-site.
The objectives with the earthworks were to allow the construction of the large flat building pads required for industrial use, with building levels above the 1 in 100-year (“Q100”) average recurring interval (“ARI”) flood level; facilitate site access to the proposed development site from nearby Reconciliation Road and the proposed internal road network; drain the stormwater from the development site, and facilitate the eventual industrial land-use applications. The steep embankments formed by the former quarry walls on the western side of the site would be stabilised, and the subsided section also remediated.
It was advised that the conditions of the site would need to be taken into account with building design. Pad footings would be suitable for foundations on controlled fill or rock, limited to a maximum safe bearing value, and piering would only be required to support buildings with high loads or tolerances over areas of uncontrolled fill. Comprehensive recommendations were also made by Costin Roe, in conjunction with the geotechnical consultants PSM, for the construction of slabs and pavements, site management requirements, erosion and sediment control, road widths and alignments, road pavement construction, and pedestrian facilities.
Emphasis on water conservation and water quality
Prior to preparation for development by DEXUS the site had no formal stormwater management or drainage. The design needed to incorporate the principles of Water Sensitive Urban Design (“WSUD”) to target the pollutants present in the stormwater so as to minimise the adverse impact these pollutants could have on the receiving waters, such as Prospect Creek. Collected roof water is generally free of pollutants, but a bio-retention system would be needed to address the gross pollutants, sediments, nutrients and hydrocarbons that are typically present in stormwater runoffs from car parks, roadways, and paved areas. Rainwater harvesting would provide for re-use as part of future individual building development applications and minimise the site’s future reliance on potable water supplies for purposes like flushing toilets and irrigating landscaped areas.
Regarding flood management, often an issue with industrial building development in some low-lying areas of Sydney, the development lots of the future Lot 18 subdivision would not be subjected to localised flash flooding, nor would the overall estate be affected by any larger regional flooding issues. Buildings would need to be set at a level 500mm above the Q100 ARI water level. Assessment by Costin Roe Consulting confirmed that the overall perimeter drain design completed by GHD in the early planning stages would be able to contain the Q100 ARI storm flow. The perimeter drains were re-documented by Costin Roe and constructed as part of the Boral earthworks exercise once approval for the subdivision and preparation of the site for development was achieved. DEXUS has successfully constructed several facilities in the northern and western sectors of Greystanes Estate, Costin Roe Consulting being involved in either or both the civil and structural engineering.