The Second Three Months Work.
THE work of the first three months was mostly preparatory. The pick, shovel and axe of the clearing gang were soon replaced by time and labour-saving devices, so that during the second three-monthly period ending January 31st, 1924, the adventure of linking Sydney and North Sydney progressed in earnest. The thew and muscle of the workmen and those busy little drills of steel, which chatter their way into the rock at 1200 beats per minute, made possible the scheme of the Chief Engineer to commence both the tunnel headings early in the new year. Each heading, about 8ft square, has been carried forward steadily but surely. About next boat-race day the headings from either end will be nearing each other, and should "Shore" score a win on that occasion the imprisoned thunder of the blasting in the headings below will echo to the tumultuous shouting in the school grounds above, particularly as Mr. K. Fraser, the resident engineer, is an old "Shore" boy and Mr. Bradfield has more than a passing interest in the school.
The open cut excavation between Bay-road station and Graythwaite has also been speeded along, and between those rugged vertical walls of rock as viewed from the train there is space for four lines of railway, whilst the sandstone, bedded ages ago in the deeps of time, has proved hard and strong enough to be used as metal for the concrete retaining walls and tunnel linings. A Hadfield's rotary crusher with a capacity of 15 to 20 tons of crushed stone per hour has been erected. The crusher is electrically driven by a 25-horse-power 440-volt three-phase motor. The crushed stone will pass over a screen; all the stone and about half the sand required for making the concrete will be obtained from the sandstone excavated, and the balance of the sand required will be obtained from the Nepean River. Armstrong Holland concrete mixers, electrically driven, have also been installed, each having an output of 90 cubic yards of concrete per day of eight hours. The concrete is mixed five volumes of crushed sandstone to 2½ volumes of sand to one of cement. Concrete test blocks, at seven days old, crushed with a load of 71 tons per square foot: at 28 days the crushing strength had increased to 142 tons per square foot. The strength of concrete increases from month to month, and, unlike stone, it does not, disintegrate by exposure to the atmosphere.
The excavation for the retaining walls between Euroka-street and Bay-road station is almost complete, and these concrete retaining walls will shortly be constructed. When complete the area between Carr-street and Euroka-street will be filled in with spoil, a new street formed, and the land fronting the new street resold or made into a little park.
AT each compressor station a cooling tower has been erected to enable the circulating water to be used over and over again. In compressing the air to 100lb. per square inch, for operating the jackhammers and pumps, mechanical energy is transformed into heat, and the cylinders of the air compressors have to be water-cooled. The base of the tower consists of a timber stand, and seated thereon a 400-gallon tank. Above the tank is a louvred tower about 18 inches square and 12 feet high, open on two sides to allow the wind to blow on the water and so cool it. At the bottom of the stand is a second tank. The water is run through the jacket of the compressor from the main water supply, and after passing the jacket flows into the lower tank at a temperature of anything from 100 degrees Fah. to maybe nearly 180 degrees Fah., according to the season of the year and if the compressor is being driven to its maximum. A small air-driven feed pump lifts the water to the top of the cooling tower, down which it trickles into the upper tank, and in so doing is cooled to the temperature of the air. From the upper tank the air-cooled water gravitates through the jacket of the compressor, so the main water supply is drawn upon only to make up evaporation losses and leakages. This simple application of the physics taught us in our school days will save millions of gallons of water annually in the construction of the city railway and the bridge approaches.
At the site of North Sydney station, a small steam navvy is being erected to load the spoil more expeditiously than by hand labour.
The abutments of the Euroka-street bridge have been completed — also the centring to enable the reinforced concrete arch to be constructed over the street. The arch would have been completed before the end of January, but the work was held up owing, to the shortage of cement.
Rock totalling 22,975 cubic yards has been excavated and tipped at Lavender Bay and Berry's Bay, whilst 1143 cubic yards of concrete have been placed in position during the second three months. Since work commenced 36,352 cubic yards have been excavated and 1183 cubic yards of concrete placed in position.
Portions of the escalators for Lavender Bay station are arriving. These will shortly be put in hand, as will also the diversion of the tramway along Dind-street. The remodelling of Lavender Bay station is well in hand.
Mr Bradfield has frequently inspected the site of the bridge with prospective tenderers, and during the past three months has had many interviews with tenderers. The correspondence with tenderers both in Sydney and abroad has also been considerable.
TENDERS closed on January 16th. and six firms in all submitted tenders : —
(1) Sir Wm. Arrol and Co., of Glasgow, in conjunction with Sir John Wolfe, Barry, and Co., London.
(2) Dorman, Long, and Co., of Middlesbrough, England.
(3) Goninan Bridge Corporation of Newcastle, N.S.W. in conjunction with Mr. Strauss, of Chicago, and Baume and Marpent, of Haine, St. Pierre, Belgium.
(4) The Canadian Bridge Co. of Walkerville, Ontario.
(5) The McClintic Marshall Products Co., of Pittsburgh. U.S.A.. who have also submitted a tender on behalf of Mr. C. A. P. Turner, of Minneapolis, U.S.A.
(6) The English Electric Co., of Sydney, in conjunction with Dr. Steinmann, of New York.
Mr. Ball, in authorising the construction of the northern railway approach some six months before tenders closed, did so on the assurance of Mr. Bradfield that satisfactory tenders would be obtained. The result of the tenders has justified the confidence which the Minister had in the Chief Engineer and the day when the tenders were opened Mr. Ball was able to announce, that the result of tendering was quite satisfactory and that a tender would be accepted.
The good progress made during the first three months has been maintained during the second three months, which should be satisfactory to the public paying the bridge tax. Buffeted by the winds of circumstance since the days of Sir Henry Parkes, the Sydney Harbour bridge is now becoming a reality owing to the planning and thoughtful mind of the Chief Engineer, who has shaped all bridge matters during the past twelve years, and to the Minister for Works and Railways, who secured the sanction of Parliament for its construction.
