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The extension of the Great Southern Railway from Menangle to Picton, was opened for traffic on the 1st of     July. The new line is a little more than thirteen miles in length, the railway now extending a distance from Sydney of fifty-three miles, or, including the Pitt-street tramway, nearly fifty-five miles from the port. No formal demon- stration of any kind was got up to signalise the event, nor did the Government offer facilities to the public for the in- spection of the line. The absence of any public celebra- tion was much regretted, as several circumstances combined to invest with peculiar interest and importance the opening of the line to Picton. It is the furthest stretch yet made by any of our railways from the sea-board into the interior. The extension is also distinguished by the magnitude of the engineering works, the greatest of these being the tubular girder viaduct across the Menangle river. The absence of any demonstration was further regretted because an oppor- tunity would bave been afforded of complimenting Sir M. Peto and Co.'s agents on the successful and satisfactory completion of their works, and at the same time of ex- pressing the regret that is entertained by many at their departure from the colony.

The tubular girder bridge at Menangle, which com- mences the extension now opened, is the most extensive engineering work that has been executed on any of our railways. This magnificent structure attracted during its erection considerable curiosity and interest, and since its successful completion and the passing of heavy trains over it much admiration has been expressed of the genius which   contrived this mode of spanning wide rivers, and of the practical skill with which the Menangle Bridge has been designed and carried out. The principle of tubular wrought iron girders which is now applied for the first time in this colony to the construction of a railway bridge has also been adopted in house building in Sydney, tubular girders having been made by Mr. Penny, of the Glebe, for the Australian Museum, and for Mr. Lasseter's new building in George-street. The principle is simply this-- that wrought iron plates rivetted together at the sides and ends so as to form a box or succession of boxes, posess the strength and power of resistance of solid bars of iron of the

same dimensions.

It was at first intended that the bridge at Menangle should be of stone or brick piers with wrought-iron girders ; but in consequence of Mr. Rhodes demanding what was considered too high a price for tho ironwork, Mr. Whitton recommended a change in the design, and drawings were made for a timber bridge. Copies of the drawings were about being prepared, when, in February, I860. disastrous floods occurred, and the rising of the river five foot higher than it had ever before risen necessitated the preparation of fresh designs, in order to raise the bridge seven feet. Shortly afterwards, however, Mr. Rhodos left the colony, and the Government being able to come to terms with Mr. Willcox for the price of the ironwork, the original plan was carried out, and drawings were prepared for a tubular iron girder bridge upon stone piers. At the beginning of 1861 the order was sent to England for the ironwork, which was made at Sir Morton Peto and Co.'s factory at Birkenhead; and in the following

October the whole of the plates and rivets were shipped in two vessels at Liverpool. One of the vessels arrived in Sydney in the following April, but the other, which contained the ironwork for the first and third spans, was unfortunately wrecked shortly after leaving the Mersey ; the loss was im- mediately replaced, and the vessels with the replaced plates arrived in Sydney, one in Ootober, and the other in December

last. The plate iron being discharged from the ships were placed on trucks and taken along the tramway and the rail-

way to within a few yards of their destination. It was about the middle of November last that the fixing of the ironwork commenced, it was finished four weeks since and consequently the work has been done in little more

than six months.  

The width of the Nepean at Meningle is at ordinary times only about seventy feet, but the slop of the banks is so gradual that the distance between the points at which the railway meets the opposite embankment is , 1912 feet. Consequently, besides the tubular girder bridge across the river, it was necessary to construct a timber viaduct upon either bank , that on tho northern bank is     980 feet in length, and that on the southern 440 feet . The iron girders rest upon four stone piers, the proportions of   which were designed with a regard to the immense weight they would have to sustain. Their extreme dimensions at the base are eighty feet by twenty, tapering upwards to fifty-two feet by twelve, they are oval in shape, and ter

minutes at the top with an impost course. They are not   entirely solid, but are constructed with vertical openings by which a large quantity of masonry is saved without any   diminution of strength. Some difficulty occurred in finding the stone for the piers, that obtained from the quarry first opened proving unfit for the work. Subsequently a sand  

stone quarry was discovered on the bank of the river about a mile and a quarter from the spot, and a railway was at once laid between the quarry and the bridge; being on an   easy incline, the loaded trucks ran down without any traction A temporary staging was carried across the bed of the river, upon which double rails were laid, and by means of an endless rope the loaded trucks carried down the blocks of stone to the piers, their descent on the one line exerting the force by bringing up the empty trucks on the other . The first pier stands on tho northern bank, and was erected without much trouble, but great difficulty was experienced in obtaining foundations, in the bed of the river, for the middle piers. Repeated and discouraging obstacles were encountered in sinking for foundation for the third pier a vast quantity of debris and soil had to be removed, and an immense coffer dam to be constructed, steam engines were employed night and day to pump out the water, but it   appeared impossible to prevent its inflow. To give an idea of the amount of labour and anxiety which the construction of the third pier involved, we may state that a depth of twenty-eight feet below the water level had to be excavated to obtain the foundation. The fourth pier, which is on the southern bank, does not rest upon the rock, but upon a timber platform fixed upon parallel rows of bearing and sheathing piles, the former were driven down to the rook at depths of from forty fivo to sixty feet, the latter were only driven about eight feet below the platform their use   being to prevent the sand from being washed away from around the piles. On the top of the bearing piles long

tudinal and transverse sills were placed, covered with two layers of diagonal planking, and upon these the masonry was laid. The blooks of stone were cut at the quarry in sixteen-inch courses and dressed. The total amount of masonry brickwork and concrete contained in the piers, is

7300 cubic yards.

Before the masonry of the fourth pier was finished, commencement was made with the fixing and riveting of   the iron plates. These, as we have said, were conveyed by   the tramway and the railway from the ship's side to the   vicinity of the bridge. As temporary supports for the girders, while being fixed, three bays of piles were driven between each pier, and the staging brought to the required level. The viaduct to the northern pier having been com- pleted, a continuous line of rails was carried upon the staging between the piers, and by means ot travelling crabs worked by steam, the plates were picked up and carried to their intended places, where they were properly fixed and rivetted. In describing the shape of the bridge, we may say, that it consists of two parallel upright longi

tudinal tubular girders twenty-five feet apart, joined at their lower extremities with cross girders, the shape being that of the letter U, with the corners squared. A section of either longitudinal girder presents one oblong upright compartment nine feet in length by twenty inches in width, with two small compartments below, called bottom boxes, eaoh about eighteen inohes square, and with two boxes above of similar size, Tho entire height of either longitudinal girder is twelve and   a half feet, the top and bottom boxes projecting beyond the sides of the girders. The plates, which are mostly half inch in thickness, are rivetted together with angle and T shaped   pieces, in addition to which there are, inside the girders, at intervals of three feet, cross plates above and below,   leaving the centre open for a space of about two feet, so that   until the pilasters are fixed a person can see from one end of the tube to the other. The cross, or kelson girders are not tubular, but merely plate girders, they are about twonty-five feet in length, and are placed three feet apart, their ends being riveted to the bottom boxes . Ironbark   planking is laid above the girders the entire length of the bridge, a single line of rails is laid along the eastern side, the western side being available for road traffic in the event of its being required for that purpose The level of the rails is about sixty-three feet above the bed of the river, it is however only six feet above the level of the floods of I860, when the river rose upwards of fifty feet . The iron- work contained in the girders amounted to 1050 tons, and thero were no less than 245,000 rivets used.

The two viaducts, of which the approaohes to the bridge upon either bank consist, are formed of bays of four upright piles and two battering piles, fixed with walings and braces, with openings of twenty five feet; the superstructure consists of double longitudinal girders above the corbels, with transverse joists between, the planking is laid upon the upper girders, and above this is the ballaating and the permanent way. In the construc

tion of these viaducts, and in the joists and planking of the bridge, 76,000 cubic feet of timber were used. The entire cost of the bridge, including the approaches, has been

about £80,000.

The official testing of the Menangle Bridge took place on Monday, the 29th ultimo, and a number of gentlemen left Sydney by special train for the purpose of witnessing the experiments. The party consisted of the Engineer-in-Chief for Railways (Mr. Whitton), the Assistant Engineer (Mr. Mason), the Commissioner for Roads (Mr. W. C. Bennett}, the Superintendent of Telegraphs (Mr. E. C. Crick- nell), Captain Mann, Mr. J. Bussell, the Rev. W. B. Clarke, and several officers of the Railway Department. Soon after arriving at Menangle, where they were met by Mr. Willcox, a test was made of the strength of the northern timber viaduct by means of a rod attached at the top to a girder in the centre of one of the openings, and which pointed to a gauge reading on the ground underneath. A heavy train was driven down and up at flull speed along the viaduct,

and the deflection in each case was found to be only three-eights of an inch. Subsequently the party preceeded to witness the testing of the more important and interesting part of the structure. For the purpose of ascertaining the amount of deflection, wire had been stretched close to each of the main girders ; its ends were attached to posts resting on the tops of the end piers, and kept tight by heavy weights. Along the side of either girder were a number of cards marked off with eighths of an inch ; and the elevation of the wire on any of these scales indicated the deflection of the girder at that part. A theodolite was also fixed on the parapet of one of the piers, from which observations were taken during the testing. The ordinary traffic along the bridge,

will be upon a single line of rails, but for the purpose of applying the most severe test that could be obtained, second line was laid down, and five of the heaviest locomo- tive engines on the line were brought to the spot. Three of these engines coupled together were placed is succession

over each of the openings, upon one line of rails; and while there, the other two engines, drawing a train loaded with iron, weighing about two hundred tons, were driven at full speed on the other : the total weight at one time upon the span being not less than two hundred and ninety tons. The rapid motion of the long heavy train between the hollow tubes produced a loud rumbling noise and also considerable vibration, but, as will be seen from the following particulars, the deflection of tho girders was very slight. On the first (northernmost) opening tho deflection was on the up side half-an-inch, and on the down side three-sixteenths of an inch ; on the centre opening the deflection was on the up side three-tenths of an inch, and on the down side four-tenths of an inch; and on the third opening on the up side, the deflection was six-tenths of an inch, and on the down side five-tenths of an inch. These results were

severally confirmed by the theodolite. Afterwards the five engines coupled together, with all the trucks, were ran over  

the bridge, and tbe total deflection was the same as with   the previous experiment-six-tenths of an inch. Upon tbe weights being taken off it was found that the girders had settled down a little more than a tenth of an inch, We need scarcely state that, as compared with structures of the same character and dimensions that have been tested in England, the deflection ie extremely small. The experi ments satisfactorily demonstrated the immense strength the girders.  

Beyond Menangle considerable engineering difficulties were presented, and there are consequently some very deep cuttings and embankments.. Immediately beyond the southern viaduct at Menangle a high embankment carries the railway to a small hamlet known as Riversford ; be- yond this the line makes an ascent of one in seventy for a length of three miles, passing through Morton Park, where the works are rather heavy. At a short distance beyond this is the heaviest cutting on the extension-that through Spaniard's Hill, a spur of the Razorback Mountain; the greatest depth of this cutting is fifty-nine feet. Beyond Spaniard's Hill the line descends, at a gradient of one in seventy, to a deep gorge known as Harris Creek It was at first intended to have a three-feet

culvert for this creek, but the extraordinary floods there years ago showed that a larger waterway   would be desirable -, accordingly a ten-foot culvert has been built ; it is nearly two hundred feet in length, the embankment above it being seventy-six feet in height. A soon   distance beyond Harris Creek the line passes through Douglas Park, and a little further on it crosses Nicholson's Creek, where there is another ten-foot culvert. For a short distance the cuttings are rather light, but as the line ap

proacbes Picton the oountry becomes more hilly, and there are some deep cuttings through sandstone rock and free stone, which required to be blasted. Following mostly the spurs of the range, the line to Picton is extremely cuitous, and while the actual distance of Picton from Menangle is less than twelve miles, the length of the line is nearly fourteen miles.    

Since the opening of the extension as far as Menangle in September last the station has been on the north side of   bridge; but a permanent station is about to be commenced on the south side. There will be a landing platform at Douglas Park, at which trains will stop by signal only, there will be no other stoppage until reaching Picton. station at Pioton, which is now nearly finished, is eighty two feet ia length, and the platform is three hundred feet in length. Th goods shed will be of timber frame and

corrugated iron sides and roof; its dimensions will be a hundred and twenty feet by forty. A turn-table is also in course of construotion. A good road is being made from the terminus to the township of Picton, whioh is nearly

three quarters of a mile distant.

The estimate for the extension to Picton was £11,000 per mile and the cost, exclusive of tho Menangle Bridge, has not exceeded that amount. Originally only £20,000 was voted for the bridge, and it was then proposed to have curves of one in fifteen and inclines of one in seventy. Afterwards however a larger and more substantial struc ture was found to bo necessary, and a better line was sub- stituted there being no curves sharper than one in thirty and the gradients of one in seventy extending only as far as Douglas Park, beyond whioh there aro no steeper gradients than one in a hundred.

The extention was opened for traffic before all the works were completed ; these will be done in a few days, shortly after which Mr. Willcox and his assistants will quit the colony and the whole of their extonsive and valuable plant will be dispersed. Mr. Willcox und Mr. Spiller are now in Tasmania, having gone there for the purpose of nego- tiating with the Hobart Town Government terms for the construction of railways in that colony.

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