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The tubular girder bridge at Menangle is the most extensive engineering work that has been executed on any of our railways, and much admiration has been expressed of the practical skill with which it has been designed and carried out .
It was at first intended that the bridge at Menangle should
be of stone or brick piers with wrought - iron girders ; but in conseqience of what was considered too high a price for the ironwork , Mr. Whitton recommended a change in the design , and drawings were made for a timber bridge. The drawings were about being prepared , when , in February , 1860 , disastrous floods occured , and the rising of the river five feet higher than
it had ever before risen , necessitated preparation of fresh designs in order to raise the bridge seven feet. Shortly afterwards, however, the Government being able to come to terms ,with Mr. Willcox , the original plan, was carried out, and drawings were prepared for a tubular iron girder bridge upon stone piers . The ironwork was made at Sir Morton Peto and Co. 's factory at Birkenhead ; and shipped in two vessels at Liverpool . One of the vessels, containing the ironwork for the first and third spans, was wrecked shortly after leaving the Mersey ; but the loss was immediately replaced , and in little over six months from the date of fixing the first portion of the ironwork the bridge was finished .
The approaches for a distance of 980 feet on the northern side, and 440 feet on the southern, are of timber, in bays of four upright and two battering piers secured by wallings and
bracings, with openings of twenty-five feet ; the ballast and permanent way is laid on planking , resting on double longi- tudinal girders with traverse joists.
The iron girders rest on four oval stone piers of eighty feet by twenty feet at the base, tapering off to fifty-two by twelve, with vertical openings and surmounted by an impost course. The whole of the stone used in their construction was obtained from a sandstone quarry about a mile distant.
The foundation of three of the piers rests on the bed rock ; the fourth, that nearest the southern bank , on piles and concrete, borings to a depth of sixty-five feet having failed to give indications of a more secure basis . The total distance between the extreme piers is 486 feet, which is spanned by two longitudinal girders, each twelve and a half feet high and twenty-five feet apart, with kelson girders every three feet , having their ends rivetted to the bottom boxes . The girders are surmounted by a roadway composed of ironbark planking , on which the rails are laid ; the height between the roadway and the ordinary level of the river is sixty-five feet. The total cost of the viaduct was about £80,000. Nearly 1000 tons of iron and 80,000 cubic feet of timber have been used in its construction , and everything that engineering skill could devise has been done to give stability to the work : the most severe tests that could be applied have produced a deflection of only six-tenths of an inch .
The whole of the works were executed by the well-known firm of Peto, Brassey, and Co., under the immediate superinten- dence of Messrs. Rhodes and Willcox, from designs furnished by Mr. Whitton , Engineer-in-chief of the N. S. W. Railway
There are several other extensive works in connexion with the railway in the vicinity of Menangle. The fifty-nine feet cutting at Spaniard's Hill, the embankment-at Harris Creek, and other difficult works completed further on towards Picton, all of which are worthy of notice, and the magnificent scenery along the valley of the Nepean will amply repay a visit.
THE VIADUCT AT MENANGLE.-(FROM A PHOTOGRAPH BY FREEMAN BROS.)
(SEE PAGE ll.)