Bridging the gap
Plans for a bridge across the Waitemata Harbour date back as far as 1860 – a mere 20 years after Auckland’s official founding. But it took an arduous 99 years to get those plans off paper and the bridge opened.
Those first plans for a bridge over the Waitemata Harbour, by a farmer named Fred Bell, failed to attract the necessary investment and were shelved. Interest was rising though and in 1920 the Auckland Canals and Waterways Commission explored the feasibility of building a bridge. The verdict came back: “too soon”. A Royal Commission nearly 10 years later reached the same verdict, however it also said that private enterprise might be interested.
It was, and in 1931 the Auckland Harbour Bridge Co was granted a charter to build the bridge and collect tolls. But, thanks to the Great Depression, investors were again hard to find.
The 1929 Commission did leave one useful legacy, however, in the shape of a plan which established the necessary length of the navigational span of the bridge and the correct positioning, over the deeper water on the northern side of the harbour.
In 1943 the Waitemata Harbour Bridge Association was advocating a bridge as a employment-creating project to help rehabilitate returned servicemen. And in 1945, with the help of the Automobile Association, it placed a petition before parliament which led to the appointment of another Royal Commission – this time with positive results, no doubt helped by the growth in vehicular traffic which was putting insurmountable demands on the ferry service.
However, the 1946 Commission’s biggest failing was to underestimate the projected population growth in both Auckland and the North Shore. Its suggested 8250 vehicles a day would use the bridge by 1965, a figure exceeded in 1959, the year the bridge was opened.
On one point the commission was emphatic: within 15 years a bridge would be sorely needed and the preliminary work – surveys, test borings, designs, economic studies and so on – should begin at once.
In 1950 the Auckland Harbour Bridge Authority was set up to construct, maintain, manage and control a bridge across the Waitemata Harbour.
It decided on a low profile, five lane bridge with two 1.8 metre wide footpaths. For the next two years controversy over the bridge was continuous – critics variously questioned the lack of railway; condemned the proposed bridge as ugly; renewed the case for a tunnel instead of a bridge; and so on.
But through it all the authority got on with the task it was assigned and by January 1952 it was ready to call for tenders for the construction of the bridge.
After conferring with designers Freeman, Fox and Partners, the authority awarded the contract to Cleveland Bridge-Dorman Long, a partnership between two great engineering firms, Cleveland Bridge and Engineering Co and Dorman Long (Bridge and Engineering), the second of which had built the Sydney Harbour Bridge.
In the meantime, the authority had lodged an application to the Local Government Loans Board for permission to raise just over £8 million estimated to cover the cost of the bridge, approach roads, engineering fees, property acquisition, land reclamations and interest payments while the bridge was being constructed. Then the trouble started.
Debate over the necessity of a bridge raged in the papers, the Loans Board declined the loan six months after the application, a loan in London of £4.5 million for the overseas content of the bridge was also declined by the British Government and negotiations dragged on for 10 months before Prime Minister Sidney Holland declared the bridge must wait.
But the Auckland Harbour Bridge Authority refused to give up and in December 1953, 17 months after the first loan application, Holland announced that, provided the bridge, approaches and all other expenses did not exceed £5 million, the authority could go ahead.
In London, Freeman, Fox and Partners began their design work over again, cutting it down from five to four traffic lanes and eliminating the footpaths to save £771,000, and deleting the major approach roads, saving a further £2,500,000.
Later, but before the bridge was completed, all the major access roads were reinstated as finance became available.
The work begins
The width of the Waitemata Harbour and the nature of the harbour bed dictated both the type of bridge and some of the methods of its construction.
The 244 metre navigation span was located near the northern end of the bridge. This was criticised on asthetic grounds but was necessary as the deepwater channel to the upper harbour lies nearer the northern end and siting the highest part of the bridge near the higher landfall (Northcote Point) allowed a consistent 1:20 road gradient.
Construction of the 1020 metre bridge did not always proceed smoothly or according to plan. Work started on the northern and southern abutments towards the end of 1955, and while the northern was completed without difficulties the southern was problematic.
It was built as an open-dredged cassion – a rectangular box, subdivided internally by cross-walls and having its upper and lower ends open. By excavating the mud from the inside, the weight of the concrete walls being built upwards at the same time would cause it to sink until it hit bedrock, about 12 metres below sea level. The cassion would then be filled with concrete and sand, forming a simple block about 15 metres long, 11 metres wide and 15 metres deep. Time estimated to do this: nine months.
The contractors encountered many large boulders in the ground which had to be drilled and blasted from under the cutting edges of the cassion by divers.
At times it seemed as though nothing would cause the box to sink, even though the walls were build upwards as far as possible to add extra weight. Final time for the job: two years.
Fortunately, the cassion troubles didn’t delay work on the piers. All the piers are of hollow, cellular construction and, though they look slender above the water, they are massive below. They were constructed in much the same way as the abutments, using a compressed air cassion – this large steel box, built on shore, was floated to the pier site and moored between two pontoons. Concrete walls were constructed inside the box, extending it upwards so that the top of the walls was kept above water while the increasing weight droved the pier lower. Eventually it touched the harbour bed and by pumping water into some of the lower compartments, it was permanently grounded.
The bottom surface of each cassion was recessed so that immediately after grounding only the outer edges rested on the harbour bed. Compressed air was then pumped into the space under the pier, displacing the water and creating an air-filled working chamber. Mud and rock were dug out from under the pier, allowing it to sink until it hit bedrock while the concrete walls were extended upwards.
In May 1957 disaster nearly struck on pier five. The northern edge of the pier dropped three metres, leaving the pier tilting dramatically. Fortunately there was no one below at the time and the top of the pier remained above water level, otherwise it might have fallen over completely. It took a fortnight of dangerous labour in the working chamber to right it.
Once excavations were finally complete, the working chamber was filled with concrete, the compressed air turned off, and the walls built up to their full height above the water. Plugs were removed from drain holes and from that time onwards the water level rose and fell inside the pier in step with the Waitemata tides.
Erection of the steel superstructure began in December 1956 at the southern end of the bridge, where the first two spans were built on temporary timber trestles. From pier No.5 the spans were cantilevered northward to be landed successively on piers No.4 and No.3. At about the same time a start was made at the northern end where the steelwork was erected on timber trestles over Northcote Point and then extended to pier No.1. From there it was cantilevered for 122 metres to form the northern half of the 244 metre navigation span.
Construction of the 146 metre span between piers No.2 and No.3 was the most problematic. It couldn’t be cantilevered northward from the preceding span, partly because of its shape and partly because the main expansion joint in the bridge is above pier No.3. It couldn’t be cantileverd southward from pier No.2 because the adjacent navigation span was at the time only half completed and it would have been difficult and expensive to build this span first. Temporary trestles were out of the question because of the deep water in the centre of the harbour.
So the bridge contractors devised a unique “floating in” operation, one of the largest undertaken at the time. Four pontoons were floated under the structure, which was built on top of some of the smaller spans near the south anchorage. One of the small supporting spans was disconnected from its neighbours and, with the help of the rising tide, the large span, supported by the smaller one, was lifted off its supports. It was then towed out to mid-harbour and moored until weather and tide enabled it to be floated into position on the falling tide.
From this point onwards, construction was straightforward, though a considerable amount of work remained. The southern half of the navigation span was cantivered out from pier No.2 and joined to the northern half in March 1959. The centre of the navigation span had to be jacked up and wedged, and some joints released to transform it from two 122 metre cantilevers to its final form, a 61 metre cantilever on either end with a 122 metre pin-jointed suspended span between them.
The roadway was then concreted and asphalted and lights, phones, gas and water mains, parapets and guardrails were installed.
Finally, Auckland had its bridge.
It was opened for traffic at 3pm on May 30,1959. The tolls were set at 2/6 for cars, 1/3 for motorbikes, 5/- for buses and 4/- for light commercial vehicles. The popularity of the bridge enabled the tolls to be reduced a year after the bridge opened and again 15 months later.
Open for traffic
From day one, traffic on the bridge has risen exponentially. Vehicle numbers quickly moved from 13,500 per day in 1959 to 42,000 per day 10 years later. It soon became clear the bridge needed to be expanded and in 1969 new prefabricated steel sections were bolted on to the outer edges of the bridge – box girders, two lanes on each, supported by the piers and independent of the superstructure. The box girders were manufactured in Japan and shipped to New Zealand on a converted oil tanker by Ishikawajima-Harima Heavy Industries, and were immediately dubbed as the “Nippon clip-ons”.
By 1980 traffic numbers had reached 72,000 vehicles per day and overhead lane signals were installed to provide tidal flow operation during morning and evening peaks.
By 1988 daily vehicle numbers were at 120,000 and with this rise in traffic so too rose the number of head-on accidents.
So investigations were started into the possibility of installing a moveable lane barrier, and in 1989 bridge owner Transit (as the New Zealand Transport Agency was then called) approved the project and planning began.
In November 1990 the barrier was installed and since then not a single head-on fatality has been recorded on the bridge.
When last counted in 2006, traffic numbers across the bridge were at 170,000 daily and are only projected to rise further.
From its construction, the bridge has been an Auckland icon, but even more importantly, it is the most important link in not just the city’s but the country’s transport corridor.
As the bridge celebrates its fiftieth birthday in May this year, it is undergoing work to strengthen the box girders and prolong their life, the barrier system has just been replaced with the latest model, and the NZ Transport Agency is making plans to increase cross harbour capacity by building a tunnel connecting in with the current bridge approaches.
Contractor, Auckland Harbour Bridge Special Supplement, May 2009
All articles on this website are copyright to Contrafed Publishing Co. Ltd.