|08- Pedestrian and Road Tunnels|
|TUNNELLING THROUGH THE PAST
People hurrying through the gloomy Devonshire Street tunnel from Central Station are probably unaware that they are on the site of an old cemetery. In fact, many of Australia's pioneers were buried here between 1818 and 18.67. They include the convict turned-merchant Simeon Lord, the first postmaster Isaac Nichols, and the first chief justice Sir Francis Forbes. After the Government decided to extend the railway to its present site, a tunnel was driven through the site of the cemetery. A tramway was built to a new alternative cemetery at Botany and most of the bodies were exhumed and removed to there. The grave stones themselves were relocated at various other suburban cemeteries such as Petersham, Rookwood, Balmain, South Head, Gore Hill, and Waverley.
When Central Station was completed in 1906, a pedestrian tunnel from Devonshire Street to Railway Square was opened beneath the railway. In the early 1970% the Sydney City Council and the New South Wales Government combined to build an eighty-metre $2.5 million extension to the Devonshire Tunnel under Railway Square. During the construction, workers dug past the main city gas line. They dug through old roads about a metre deep; they found several layers of tram tracks. Deepest of all was an ancient sand. . stone sewer -a forgotten piece of Sydney's convict past. The large tunnel drain 1.5 metres deep and a metre across was formed from huge, hand-hewn sandstone blocks. It ran east-west, about four metres below the present surface.
The Sydney City Council came across more reminders of the city's past on its own back door step beside the Town Hall in 1974. During the construction of Sydney Square, a bulldozer broke through a vaulted chamber about two metres below ground level. Sections of the roof collapsed to reveal the remains of a wooden-coffin inside.
The discovery came as no surprise because it was well known that the Town Hall site had been Sydney's first burial ground. From 1793 to 1820, many convicts, soldiers and several of the wealthier citizens were buried there. The site was neglected until the 1860s when it was decided to build the Town Hall and the Cathedral there.
The Sydney City Circle underground railway system opened in 1926, brought with it networks of tunnels serving Museum, St. James, Town Hall, and Wynyard Stations. The retailer Mark Foys linked with the underground system with a tunnel leading from the Museum Station to the store.
Another store with its own tunnel is David Jones. But this is a private one at the intersection of Market and Castlereagh Streets and is used as a service tunnel between the company's two retailing sites.
More recently, underground shopping centres have become fashionable around the city -which is hardly surprising considering the price of land at the surface. One of the largest is under the Hyde Park Square Office and Shopping complex between Park and Bathurst Streets. A new sixty-five-metre tunnel under Elizabeth Street was opened in 1978 to take pedestrians from the complex to Museum Station. The new tunnel was given a modern-art atmosphere with wide bands of colour. The smooth lining of the tunnel was made of a specially toughened material and was said to be vandal proof.
One of the longest tunnels in Sydney's underground network takes people from the Domain Parking Station under the Domain by a moving footway. It was opened in 1959.
A most extensive tunnel area already in existence is around Wynyard Station where a large proportion of Sydney's work force struggles up from the ground on to city streets each morning. The Sydney City Council would like to see this subterranean network extended. In 1971 the Council put forward a plan for a network of overpasses, arcades, and underpasses around Wynyard Station. The plans included using the existing subway under George Street, linked with an improved arcade and subway system. They proposed a new tunnel under Hunter Street to Australia Square. To the west the Council saw another opportunity for an underpass under Clarence Street from Wynyard Station. They proposed using the old existing tramway tunnel for a moving footway from Wynyard to Lang Park from where pedestrians could walk along to the Rocks area. They also saw an ' opportunity of using the disused tramway tunnel to the south to arrive at the southern side of Wynyard Station.
When the Eastern Suburbs Railway opened in 1979, its station at Martin Place created its own area of pedestrian underground tunnels. The Council has plans to extend the tunnels under Martin Place to Castlereagh Street.
A tunnel under Martin Place from Angel Place to the GPO which carried postal vehicles is now also used as a pedestrian passageway.
Cahill Expressway construction, January 1960.
An unusual tunnel came to light in 1975 when the Sydney Harbour National Park Authority was renovating Greycliffe House for use as its headquarters. Workmen came across an old tunnel underneath the house built for the daughter of William Charles Wentworth about 1850. The tunnel ran to a well and is still there. But when and why it was built still remains a mystery.
An unusual link with the past is the vau1ted:areas under Macquarie Street which the
Sydney City Council leases to the present owners of the adjoining buildings. The vaulted
areas were originally part of warehouses built in the 1880s.
When they were demolished in the 1950s to make way for the present, office blocks the vaulted areas were retained and are now used as car parks and storage space by the companies that occupy the new buildings.
THE CAHILL EXPRESSWAY
The Sydney City Council built the Cahill Expressway. The first tunnel on the south side of the bridge was dug before the Second World War. It was set aside for use as an air raid shelter for the nearby Fort Street Girls' High School during the war years, then had work resumed on it afterwards. By 1952, the Cahill Expressway had reached the Conservatorium, which had been built as a stables for Government House by Governor Macquarie and the convict architect, Francis Greenway, in 1816. Work then began on a tunnel under the Botanic Gardens. This section was completed in 1962. The total cost was about $8 million.
Considering how old the area is, surprisingly little of historic interest was dug up during the excavation works that followed. Some workmen did find a few sovereigns which were handed over to the police. Not surprisingly, no claimants came forward, and the coins' were handed back to the finders.
The tunnel under the Botanic Gardens runs parallel to Macquarie Street. The main work involved the excavation and construction of a four-lane, vehicular tunnel 400 metres long by cut-and-cover method, followed by the restoration of the gardens. '
The tunnel was built in open cut and, for rapidity of construction, concrete retaining walls supporting precast, prestressed concrete beams and a reinforced concrete roof were adopted. The horizontal alignment of the tunnel curved through seventy-five degrees, so, for traffic convenience and structural safety, central roof supports were omitted.
The floor level of the tunnel was controlled by the existence of the Metropolitan under-
ground railway underneath, and the minimum traffic clearance inside the tunnel was fixed
at five metres. The Botanic Gardens authorities required that at least a metre of soil over-
burden be restored. As a result of these restrictions of levels, the maximum depth of the
roof structure could not exceed two metres.
Blasting, using millisecond delay detonators, was adopted, with small charges for the
bulk of the sandstone excavation, except over the underground railway in the vicinity of
the State Library, where the Railways Department requested the use of mechanical tools
only. An architect was engaged by Council to examine, photograph, and report on
damage to buildings in Macquarie Street caused by blasting operations, and to supervise
any repairs that were necessary. Similar action was taken near the Art Gallery section of
the work where, in addition, a seismograph was used to record the concussion adjacent to Navy oil storage tanks at the off-loading ramp.
Soil and rock rubble from the excavation were loaded into a fleet of thirty trucks by
means of two hired Public Works Department excavators. Surplus material was deposited as filling for the new Circular Quay Overseas Wharf and in t 'Le approaches to the Department's new bridges at Gladesville and Fig Tree.
The tunnel walls are of reinforced concrete construction on spread footings and are designed to support the roof system.
Associated with the tunnel construction were the problems of providing sufficient
ventilation and adequate lighting. For ventilation two multistorey fan rooms were constructed below ground level, one to serve each half of the tunnel. The southern fan room was built on both sides of the roadway, the division being necessary because of the heavy loading on the electric train tunnels underneath the pavement which would have been imposed by a single large structure. A heavy-steel, portal-frame construction was adopted over the train tunnels to support the fan rooms and the roof system, the footings of the frame being carried down to rail level.
Inside these ventilation rooms four supply and four exhaust fans are located of total capacity amounting to 360 kW. This system was designed to renew the air supply in the tunnel every two and a half minutes. Fresh air is supplied through reinforced concrete ducts below the tunnel pavement feeding into pipes with metal wall outlets about nine metres above floor level. Stale air is exhausted through metal ducts in the ceiling and 1s drawn between the ceiling and through the diaphragms between and at the end of the beams.
Carbon monoxide detection equipment consisting of two enclosed units is located in each of the switch rooms in the northern plant room and the southern plant room on the west side. The units contain a Parson's infra-red gas analyser calibrated to read 0-400 parts per million of carbon monoxide in the air, a sequential sampling switch and the necessary solenoid valves and sampling pumps to sample continuously from two sections of the tunnel.
Cahill Expressway construction, October 1961. The entrance to the underground section is opposite the NSW State Library.
The installation of the carbon monoxide monitoring equipment was considered essential from the safety point of view. In the event of an accident occurring in the tunnel, the . traffic build-up would increase the concentration of carbon monoxide, but, with the monitoring and recording equipment in operation, a continuous check is made for dangerous concentrations. Without this equipment the fans would be operated manually, most probably for periods in excess of those required to ensure that carbon monoxide concentrations are at safe levels. The designers felt that this would result in an unnecessary increase in power costs.
In lining the tunnel, the designers faced problems of fireproofing, rot and corrosion resistance, ease of cleaning, and selection of lightweight materials which would not impose a high dead-load on the roof beams. These requirements were adequately met by the use of aluminium sheeting for the ceiling and ceramic tiles for the wall lining. .,
If a fire occurs in the tunnel, a flashing amber signal operates from the fire alarm system at the tunnel's two portals for three seconds, followed by a red signal and a neon sign indicating "STOP". An automatic sprinkler system has been provided as well as a large capacity fire main with hydrants placed at seventy metre intervals. Vehicles carrying explosives or inflammable liquids are not permitted to use the tunnel but must detour via Macquarie Street to avoid the possibility of being the accidental cause of a fire in the ., tunnel.
THE KINGS CROSS TUNNEL
People had been talking about building a tunnel for twenty years when work on the 270-metre, four-lane tunnel through the heart of Kings Cross began in 1970.
The first aspect of the investigation work involved consideration of how long, and at what depth, the tunnel should be built. Both technical and economic factors were taken into consideration. The technical factors had to include geological studies of the rock which would be encountered, to check such details as its hardness and uniformity, projected traffic volumes, and the possibility of using a tunnel-boring machine.
Following consideration of these factors, the decision was made to adopt a short tunnel
at a relatively shallow depth to be constructed by the cut-and-cover principle, rather than by boring or mining methods.
Before detailed design could proceed, it was necessary for a large amount of subsurface
exploration to be carried out. This involved drilling and coring at over fifty test sites, to
depths of up to twenty metres. The cores from these drill holes were subsequently examined to determine structure foundation levels and appropriate excavation batter slopes. In addition, unconfined compression tests were carried out on the rock at foundation levels to determine their bearing capacity. The rock was Hawkesbury sandstone, with some layers of shale and clay.
In the popular Kings Cross area, there is a particularly large number of public utility
mains. Before any construction could be commenced, relocation of these mains was
necessary. During construction of the tunnel, public utility services had to be carried
across the tunnel in special ducts on the bridges at each portal. Other services,, running
parallel to the tunnel, were located in surface streets. The Department of Main Roads
decided that public utility services would not be laid in the tunnel roadway and this would
avoid any future interference to through traffic by the utility authorities.
Before any construction work was commenced, acquisition of the required land was
necessary and, consequently, 118 properties were acquired by notification in the Government Gazette of 28 February 1969.
Owners were advised by letter of the effect on their properties and were invited to lodge a claim for compensation. The claims were assessed by the Valuer-General's Department and these valuations (which were based on the Kings Cross tunnel construction, December 1974 market value of the properties at the date of resumption) formed the basis of the Department's negotiations. As well as the propertv owners, approximately 600 tenants were affected by these proposals. Tenants who had a compensable interest were able to submit a claim for compensation and these claims were also assessed for the Department by the Valuer-Generals Department. A number of tenants received special consideration by the Housing Commission and were allocated alternative accommodation.
The tunnel has certainly improved the flow of traffic but, at the same time, it has removed much of the character from the Top of the Cross, which was once a city landmark. Driving up William Street and through the modern tunnel today, it is hard now to visualise the Top of the Cross as it was in 1970, when a mass of tawdry signs tempted the travellers to avail themselves of the delights of the Stripperdelic and the more mundane pleasures of Coca Cola. Most of the 800 residents and shopkeepers affected were opposed to the plan. In 1969, 300 of them marched on Parliament House to protest against the tunnel. They wanted the Department to tunnel deep under them like the Eastern Suburbs Railway. But, as the Department pointed out, it was much cheaper to remove the top and then put a lid back over it than to burrow a deep tunnel under the Cross. So down came, the Top of the Cross, and through went the tunnel.
And so work began on 19 June 1973, with the bulk excavation for the sandstone cutting which contains the sides and bottom of the tunnel shell.
Excavation was carried out by trenching with jackpicks and ripping with a dozer. No major problems were encountered during the excavation and, by January 1974, the bulk of the material had been excavated.
The completed Kings Cross tunnel, December 1975.
During excavation some vertical cracks parallel to the face occurred in the rock berm, making it necessary to stabilise the rock face with rock bolts. The release of the restraint when the rock was excavated for the tunnel resulted in minor outward movement of the vertical rock face in a few isolated areas so that some trimming back of the rock was required.
At a future date, the air space above the tunnel will be used for property development.. Columns and footings were constructed, as part of the project, to accommodate this proposal. Excavation for the columns was carried out concurrently with the bulk excavation. The footings for some of the columns were excavated by undercutting the rock face.
The roof of the tunnel consists of precast concrete beams and girders with in-situ concrete infills between members. The precast members were cast at Blacktown in Sydney and transported to the site where they were placed in position by cranes.
The tunnel walls are lined with an asbestos cement sheet wall cladding.. There were minor difficulties in maintaining alignment of the asbestos cement sheeting where the sidewall sections were misaligned during erection.
In the design of the work, consideration was given to the construction of a sunscreen over each tunnel entrance to lessen the effect on motorists of a sudden change from full sunlight to tunnel lighting. However, the high level of lighting provided in the tunnel made sunscreens unnecessary. Four rows of fluorescent and sodium lights illuminate each tunnel cell and; in the event of a power failure, there are thirty-four incandescent battery operated emergency guidance lights which switch on automatically. To counteract glare from the rising and setting sun, the levels of illumination are co-ordinated in the interior and at the thresholds of the tunnel.
The estimated cost of the entire project was $21.3 million, which includes $13.1 million for the acquisition of land and $8.2 million for constructions.
|This section is based on the excellent book by Brian and Barbara Kennedy. (Subterranean Sydney (The Real Underworld of Sydney Town), Reed, Sydney, 1982. ISBN 0 589 50312 X). Copyright Brian and Barbara Kennedy and Reed Publishing.|