A prison built on aggregate

Over two million tonne of quarried product was used in the construction of the new Otago Regional Corrections Facility at Milburn in South Otago. Blackhead Quarries manager Gavin Hartley provides a hands-on view of the project’s scale.   BY ALAN TITCHALL

Fifteen South Island quarry operations from Christchurch to Invercargill supplied product to recently opened corrections facility in South Otago – a project the size of a small township that was literally built on local aggregate.

Gavin Hartley found himself right in the thick of the project while employed with Fulton Hogan Dunedin, who undertook all work below the slab. In awe of the contribution of the quarrying industry to its construction, Hartley kept track of source material details for a presentation at the Quarry & Mining conference this year.

Hartley, a qualified geologist with an A-grade quarry manager’s ticket, become a quarry customer rather than a supplier for two years when he was moved to Milburn to work as site engineer on ‘project Crioch’ – the two-year construction of the Otago Regional Corrections Facility (ORCF). One of four new corrections facilities built in New Zealand, it houses 1600 inmates.

Physical work started on the project in December 2005 (a record wet month) with the new Narrowdale Rd linking State Highway 1 and the Milburn corrections site that sits in the middle of a diary farm.

“From an extraction industry point of view, the ORCF project was the equivalent of an 800 person, 300 house subdivision, with buildings, road construction, under ground services, water, waste water, pump mains, lighting, etc,” says Hartley.

Major works started in January 2005 with the site stripped by scrappers. Located in the middle of a dairy farm, cow lanes and stock watering systems were the first things to be re-established, says Hartley, which wasn’t without conflict with a share-milker leasing land from the farmer.

Over 90 percent of the foundation aggregate for the site was sourced from the southern east coast of the South Island.

The first rock used was for the strengthening of Narrowdale Road and construction of new cow lanes around the site. The rock was sourced from two quarries – the old Milton Borough Council Quarry (that used to be managed by the Clutha District Council and is now operated by Blackhead Quarries), and Blackhead’s Balclutha Quarry.

“Balclutha also supplied basecourse, dust, sealing chip and concrete aggregate to the project. Raw feed was sourced from both a greywacke hard rock quarry and gravel extracted from the Clutha River.”

A mobile crushing plant working out of the Marshall Quarry, a basalt cone 10 kilometres north of the site, produced the majority of the basecourse, says Hartley.

The main area of the site, measuring 650 metres by 150 metres, involved 33 kilometres of under ground services for storm water, waste water, ducting, power, security, potable water, fire water and gas. Many services were placed in the same trench.

Around 27 concrete panels for buildings and a five metre high, 1600 metre long perimeter wall to keep inmates in, were precast on site.

“The remaining panels were cast in yards from Invercargill to Christchurch, and all required high quality concrete aggregate. Buildings were clad with a hundred tonne of Eterpan (fibre cement board) and 11,5400 cream-coloured blocks supplied from the Oamaru Sand & Shingle plant at Hilderthorpe. Altogether, cladding and block walls required 1450 tonne of aggregate, says Hartley.

Some building windows are 25mm thick with raw product for the finished glass (imported from Europe), is made up of 72 percent silica sand, 13 percent soda ash, eight percent limestone, and four percent dolomite.

Within the perimeter wall, buildings are linked with three metre wide concrete footpaths and Allied Concrete set up a batching plant on site to supply concrete for these paths and the precast yard, says Hartley.

“Allied’s concrete aggregate was sourced from Blackhead Quarry, Walton Park Sand in Dunedin and Southern Aggregates’ sand plant in Invercargill. Immediately inside the perimeter wall is 10-metre wide chip sealed sterile zone enclosed with a taut wire fence (three metres high with sensored barbed wires), and an internal chip sealed road that goes around the entire site. The total chip sealing for the project, including works to Narrowdale Road and the access road, amounted to 52,400 square metres, or 1300 tonne of G3 and G5 chip.”

The project had its unusual features, including what proved to be a very expensive water feature in its ‘spiritual centre’ that is made from rock found in the Catlins and boulders sourced from each major river in the Otago Southland area – supposedly for cultural considerations.

Talkback radio also frothed over news that the cellblock floor was to be internally heated. As Hartley says, underground heating is not all about prisoner comfort. Security-wise, it’s far safer than a wall-heater that can be ripped from a wall and used as a weapon.

Then there are the realities of the Southland climate. The winter proved so cold during construction that the water in the under floor heating pipes froze and burst in places, and had to be topped up with anti-freeze.

The prison was handed over to the Corrections Department in March 2007, and a few months later Hartley was given the job of quarry manager at Blackhead Quarries.

“Most of us already appreciate the scale of the contribution the extraction industry plays in society, but few projects get recorded in detail. I hope these figures may be of some use to quarrymen in the future when trying to convince councils or politicians that our industry is very important to the well being and growth of our communities,” he says.

Otago Regional Corrections Facility facts and figures

Quarried products totaled 213,580 tonnes: Rock 60,000; concrete aggregate 22,910; dust/sand 23,780; basecourse 104,150; sealing chip 1300; and asphalt aggregate 1440.

Rock source was: River 16 percent, beach one percent, pit four percent, and hard rock 79 percent.

Product percentage breakdown: Basecourse 48 percent, rock 28 percent, sealing chip one percent, asphalt aggregate one percent, dust/sand 11 percent, and con. aggregate 11 percent.

Quarried products were produced from 15 operations from Christchurch to Invercargill, ranging from 50 tonne of schist walling rock to 92,000 tonne of basecourse. Production of quarried products equated to 14, 000 man hours and contributed $320,0000 to the economy in wages over an 18 month period.

The project required infrastructure for both potable water and wastewater. Two 470 cubic metre wooden tanks were built to store drinking and fire fighting water. The supply line from the Milton water plant was constructed under a separate contract.

Wastewater is pumped up to two primary sewerage ponds that hold 15000 cubic metres. They were excavated in a paddock lined with 200mm of filter material (5000 tonne of 5-10 mm rice) and covered with a PVC mat. The second of the two ponds has two filter bunds made of 60 –100mm rock (2200 tonne). The discharge is then gravity feed to the wastewater plant in Milton.

The designation conditions required bunding, landscaping, amenity and screen planting.

Some 35,000 plants were planted in and around the site. Landscaping used quarried products including feature rocks, schist rock walls from Poolburn, sand for leveling sports field, agricultural lime to get grass growing.

Two creeks on either side of the site required a number of new and upgraded culvert crossings with concrete pipes up to 1800mm in diameter and scour protection with rip rap, yet another quarried product.