Costin Roe Consulting was engaged by Investa, one of the largest property groups in Australia, to provide a condition report on the assets surrounding the planned redevelopment of 60 Martin Place, Sydney.For Lee Carroll, MIEAust CPEng MEng, Senior Engineer (Remedial/Forensic), Costin Roe Consulting, this would mean first-hand examination of buildings, basements, vaults, tunnels, and some rarely-seen voids beneath the “civic heart” of Sydney.
Vertical and horizontal stresses in the ground
The role of the engineer is essential in the project-planning of urban redevelopment. Demolishing a multi-storey building and excavating for basements removes weight from the site, which in turn relieves the vertical stresses on the subsoil and substratum below. Constructing a taller building on the same site produces greater vertical stresses than existed before. The spring-like movement of the ground during demolition and construction, if not properly assessed and managed from the outset, could potentially compromise the integrity of buildings and infrastructure nearby. Pre-development condition reports by experienced engineers are required for reliable reassurance and guidance, if necessary, to insurers, project partners, and the owners of surrounding buildings.
In urban Sydney there are not just the typical vertical stresses of demolition and construction for the engineer to consider, but also horizontal stresses caused by natural forces. There are fault lines running deep beneath the Sydney basin dating back to when New Zealand started breaking away from Australia more than 85 million years ago. The Australian continent is also moving northward, away from Antarctica, at the rate of 5.6cm per year.
“The horizontal stresses in Sydney affect rock excavation. The rocks can move between .5mm and 2mm per metre of excavation. If you excavate down 20 metres for a basement, the rock can move 20mm laterally,” said Lee Carroll.
Redeveloping a non-descript building into a landmark
Investa’s proposal for the redevelopment of 60 Martin Place promised to transform an uninspiring, inefficient, 1970s-vintage office block of 28 storeys into a sustainable, contemporary 33-level complex with two additional basement levels. An international design competition was won by architects Hassell in February 2015. The condition report by Costin Roe Consulting would involve inspections of above-ground and below-ground assets within 50m of the boundary of the proposed redevelopment site.
On the corner of Macquarie Street and also Phillip Street, 60 Martin Place is right next to the heritage-listed St Stephens Uniting Church (1842) and the Seven Network’s Sydney News Centre. Just across the road, in Macquarie Street, is NSW Parliament House (1816) and Sydney Hospital (1811). The entrance to Martin Place underground railway station is virtually on the front doorstep, and directly opposite in Martin Place is the headquarters of the Reserve Bank of Australia.
Underground railway tunnels and the RBA vaults
“To assess the Reserve Bank of Australia site we needed to examine the underground vaults. There were armed guards present the whole time. The report had to be written on the site, and left on the site. The security around our inspection was extreme, of course, but it was no barrier to getting the assessment done,” Lee said.
Five busy railway tunnels extend beneath the eastern end of Martin Place. There are three City Circle tunnels, two Eastern Suburbs line tunnels, and also Martin Place station (1979). For OHS/WHS and public safety reasons, these subterranean areas were inspected in the middle of the night, when the trains were not running.
“We could access the active rail tunnels between midnight and 3am only,” said Lee. “I was accompanied by surveyors and rail protection officers. It was pitch black in the tunnels after-hours but with the lighting we carried I was able to examine the condition of the tunnels as needed and assess any cracks or defects if found.”
The abandoned tunnel almost no-one has seen
Radiating from St James Railway Station are several railway tunnels which have never had a train pass through them. Built in the 1920s, the onset of the Great Depression and then WWII meant these tunnels were never connected to the main lines. The tunnel structures are so solid they were used as mass bomb shelters during WWII. The army’s attempts to blow up the tunnels after the war were unsuccessful and so they remain today, completely closed to the public, and almost never intruded upon.
One of these tunnels extends about 1 km from St James towards Martin Place. Lee Carroll was required to go underground and inspect this cavernous, abandoned stub of a tunnel on his own – taking a selfie (above right) as a memento of this rare and perhaps once-in-a-lifetime experience.
“We inspected the tunnel linings for cracking, spalling, leaking or any other kind of defects and prepared detail drawings showing their locations to enable comparison at future stages of the project,” Lee said. “It’s also a credit to the city that we encountered no rats.”
Condition report facilitates start of transformation
With the inventory of assets in the zone surrounding 60 Martin Place satisfactorily detailed and assessed in the Costin Roe Consulting condition report, the redevelopment by Investa Property and Gwynvill Group (the “owners”) would begin with demolition work starting in early 2016. Project completion is set for 2019.
The new development, named “Sixty Martin Place“, will offer more than 40,000m² of commercial and retail space at one of Sydney’s most desirable and accessible CBD locations. Supporting both Council’s Sustainable Sydney 2030 vision and the objectives of the Martin Place Owner’s Group, the owners’ aim is for the Sixty Martin Place building to achieve 6 Star Green Star/5 Star NABERS ratings for environmental efficiency.
Image of Martin Place Railway Station by Photographic Collection from Australia (Railway Station – Martin Place)
[CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons.