JULP1899. $55

BAILWAP VIADUCT8 HN COBNWAEL, OLD AND NEW, - BY MR. 11'. M. GIBBONS, DIVISIONALENGINEER, GREATWESTERN RAILWAY, .

Great Western Railway Qld Viaducts in Cornwall. The course followed by the railway from n?lynaonth to TEUM, opened in 1859 and extended to Pdmouth in 1863, traverses mmy cross vdleys of depth too great to be economically filled up by embankments. Excluding the Eoyd Anherf Bridge at Baltash, forty-two viaducts were placed on the 65 miles bebwwn Plymouth and FaPmouth, snd ten viaducts on the 26 miles between and , Plate 92. The aggregate length of the forty-two viaducts was 4 8 miles, and of the ten viaducts 1.03 mile. Without going too closely into the detains of construction, which would be out of place in the general description called for on this occasion, all the above numbered viaducts may be placed under one Of %WWO CkbSSeS, ib 01 B. Those in class A depend upon timber trusses to carry the decking and the railway, and these trusses are supported for the most part on timber piles which form the piers. This kind of construction is to be ff~~d0etween Devonport and 8t. Germans, where the railway hser to cross tidal creeks, in which are deposits of mud of depths up to 70 feet. Hence followed the adoption of timber piles for fomdations, carrying timber piers and trusses. 40 feet is the usual span for thie class of viaduct, and the heights range between 40 and 100 ffwt. There are three principal viaducts of this type :- Weston Mill, 396 yards Bong and 46 feet greatest height. (This viaduct is to be replaced by a steel structure on the western side, and the works at the south end are in progress.)

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Forder, 202 yards long and 67 feet greatest height. Nottar, 378 yards long and 67 feet greatest height. In this type of construction the changing of the timbers in any part of the main trusses involves the breaking up of the truss, which has to be cast adrift for the time, temporary support being provided to carry the decking on one side; this occupies so much time that the renewal of the principal parts of the trusses can only be done on a Sunday, when an- interval of several hours betweerm trains can be obtained. At St. Germans Viaduct, trusses of timber with wrought-iron ties and braces cover spans up to 66 feet. There is only one viaduct like this. The length is 315 yards, and the greatest height 106 feet. The piers are framed with timber, each of the four corners consists of a cluster of four baulks 12 inches square, braced horizontally and diagonally at intervals, Figs. 4 and 5, Plate 94. The renewal of timber trusses in this viaduct has to be done on a large scale ; that is, all the upper work above the cills of the piers is renewed at intervals of something under twenty years. For this renewal a wrought-iron bowstring girder is used, which supports all the flooring on one side of a span, so that the timber truss can be taken away and a new one framed up to take the place of it. Twice has this operation been carried through this viaduct since the line was opened. If a new viaduct be not built within a few more years the operation will have to be repeated. The diagram elevation, Fig. 1, Plate 93, and the detail elevation and transverse section, Plate 94, show the largest example of Class A, or the trussed timber viaduct. In Class B may be included the large majority of the viaducts, over valleys where good foundations are to be had. The general type of construction in such cases is shown on Figs. 2 and 3, Plate 93. Drawings and photos illustrating this class are also shown on Plates 95,96, and 97. The general plan is to have masonry piers built from 60 to 66 feet apart (centres) and carried up to oil1 level, which is about 35 feet below level of rails. From the tops of these piers three sets of struts radiate, four struts in each set, making twelve struts on each pier ; these struts are kept in place by horizontal walings and diagonal braces of timber, and on the top of the struts

Downloaded from pme.sagepub.com at WEST VIRGINA UNIV on June 5, 2016 JULY 1899. RAILWAY VIADUCTS IN CORNWALL. 357 are the main carrying beams in three runs for the single line ; the beams are double and the top and bottom beams are united by raking bolts, joggles and keys. The top width of the viaduck is from 15 to 164 feet according to the construction of the parapets. The viaducts in West Cornwall, none of which now remain, had smaller spans (50 feet centre to centre of piers) and three legs in a set instead of four, the middle one being vertical; but the main object in all these designs was to facilitate the renewal of any strut or beam without disabling the viaduct for a long time. In order to change one of the legs, less than an hour mill suffice; for changing beams about double as long an occupation is needed. The general appearance of the fan-like struts and open parapets is not a disfigurement in the landscape, and several photographs ghen to illustrate new works show also the old ones. The author does not intend to deal with the at Saltash in this general paper, but hopes that tho inspection that members will make of it, will satisfy them that it is entitled to hold its own among bridges designed up to the present day. Plate 98 shows a clear view of the process of erecting one of the main tubes. When the work now going on is finished there will remain only one timber viaduct betneen Truro and Penzance, namely, the low one that crosses the beach 2 mile before reaching Penzance station. Between Plymouth and Falmouth, speaking broadly, two-thirds of the work of reconstruction has already been done, and the work is still busily in hand. The drawings chosen to illustrate the general construction of viaducts of Class B are those of Truro on the main line, Fig. 2, and Ponsauooth on the Falmouth branch, Fig. 3; both of these, shown on Plate 93, are now carrying the traffic, and are gcod examples of length and height.

New v&~hcts.-The first step towards reconstructing viaducts in Cornwall was taken in the year 1869 when the Probus viaduct, 145 yards long md 43 feet high, was replaced by an embankment, and the centre line of railway was improved at the same time. Between the years 1873 and 1886 the viaducts in the Glynn Valley between Doublebois anJ Road stations, eight in

Downloaded from pme.sagepub.com at WEST VIRGINA UNIV on June 5, 2016 358 llAILWAY VIADUCTS IN CORNWALL. JULY1599. number, and those near , three in number, mere dealt with, and mill now be briefly described. In 1873 a contract was let for the Drawwood deviation, which comprised the substitution of an embankment with a retaining wall, Plate 99, for Drawwood viaduct, the old viaduct being of the same type as that at Probus, while West Largin viaduct was replaced by a new viaduct with three arches in masonry, Fig. 17, Plate 101. Dramwood old viaduct was 227 yards long by 53 feet high, while West Largin was 108 yards long by 81 feet high. The stone used was taken from the company’s quarry at Westwood, one mile west of Doublebois Station. This quarry furnished stone for all the eleven viaducts which are now being described. The quarry yields a hard, durable, shale rock with flat naturnl beds, well suited for bridgework. Cornish granite was used for quoins of piers and arches, for impost and string courses and for coping; in some cases the Westwood quarry stone was used for dressings and for pier quoins but not for arch qucins. The mortar generally was gauged with lias lime, sand, and ashes. Proportions, 1 of lime to 14 or 2 of the other components. Edge stone mills were used for grinding the mortar. Following the two viaducts included in the Drawwood contract, the Cornwall Railway Company built the remaining nine viaducts with their own staff without employing a contractor, using their quarry at Westwood to supply the bulk of the stone. The extent of their operations may be estimated by a glanre at the quarry, which can be seen from the railway one mile below Doublebois Station and on the down line side. Nearly all the stone taken out has been used in the reconstruction of these eleven vinducts and of two others near Grampound Road which will be described further on. The valley under Westmood viaduct and adjoining the quarry was found to be a convenient place for tippirig ‘‘ deads,” for a great deal of the stuff excavated was not fit to use fnr building stone. Ruhble from the quarry was also used for filling up embankments, and for building dry walls at the ends of the new viaducts. Eleven viaducts mere built in this manner and in tho following order :-Drawwood, Plate 99 ; West Largin, Fig. 17, Plate 101; Penadlake, Figs. 15 and 16, Plate 100, and Fig. 18,

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Plate 101 ; Clinnick, Fig. 19 ; Westwood ; Noorswater, Fig. 20, and Plates 102 and 103 ; Derrycombe ; St. Pinnock, Fig. 25, Plate 104 ; Largin ; Bolitho ; Cartuther. Drawings are submitted of the first four ; Westwood is omitted because it is very much like West Largin. It will be noticed that segmental arches not exceeding 50 feet in span are used, the heights being nowhere greater than 80 feet. In designing Moorswater viaduct, the height of the structure, 148 feet, and the width of the valley called for increased spans, and eight arches each of 80 feet span were built. In this viaduct, as in all the others, the old structure was wide enough for a single line of rails of 7 feet gauge; while the new structure was made to carry a double line of rails of 4 feet 84 inches gauge. In building at Moorswater, the materials were delivered by rail at the top ; they were then run down an inclined plane to the pier where required, and thence lifted and set in place by one of four Scotch derrick-cranes worked by steam, which stood on stages of 70 feet in height, so that they could handle materials €or the masons at a height of 120 feet above the level of the ground. These cranes were of 3 tons register, but generally the loads were not allowed to exceed 2 tons. As soon as the centres were fixed, an overhead road, at a level of 2 feet above the crowns of the main arches, with travelling cranes upon it, was used for handling materials for building arches, spandrils, and upper works. On this viaduct iron hand-rails were used for parapets with timber outside guards, one to each line of railway. The viaducts at St. Pinnock, Fig. 25, Plate 104, and Largin, of 150 feet and 130 feet in height respectively, were the first to be reconstructed on the same axis as that of the old viaducts. The original piers are of a form which allowed of their being raised SO as to carry wrought-iron main girders, which were set outside the old timber structures; then cross girders and rail girders were added without removing any important carrying part of the original timber. As soon as the new girder work was completed underneath, the timber beams and struts which were no longer wanted to support the railway were taken out piece by piece ; and lastly the timber decking planks were removed a few at a time, and their places

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taken by Barlow rails. By this operation all periEl'hable material was removed from the viaduct, and it was cffected without any interruption of the traffic on the single line overhead. This line remained single for about ten years, and ran along the axis of the viaduct ; but when the line was doubled in 1893 the up and down roads were each placed on the side belonging to them. The line of division between the new and the old masonry of the piers is more clearly marked in the photograph, Fig. 25, than in the work itself at the present time, after the new work has been exposed to the weather in the Glynn Valley for nearly twenty years. The remaining three viaducts - Derrycombe, Bolitho and Cartuther-were re-built with masonry arches of segmental form, span being 569 feet and the rise 20 feet. Derrycombe has four arches with a central height of 78 feet. Bolitho has seven arches with a central height of 115 feet. Cartuther has five arches with a central height of 90 feet. Bolitho viaduct had to be built without the purchase of any additional land. The piers were completely builh up to the level of &post course, as they did not come opposite the old ones ; then the arches were built in two parts longitudinally ; the first part was just wide enough to carry one line of rails to the 7 feet gauge; as soon as the traffic had been turned upon the new work, the old 8ictduot was taken down and the missing width was added to the arches from end to end of the new viaduct, so as to provide for double line of 4 ft. S+ ins. gauge. By due allowance in erecting and loading the centres any crack or inequality in the line of junction of the two parts of the arches was avoided. The eleven viaducts in this section of the Pine having been completed, two were built between Burngullow and Qrampound Road Stations. The arches have the same dimensions as those of the four viaducts last described. Fa1 viaduct has seven arches with a central height of 90 feet. Coonabe (st. Stephen's), Big. 27, Plate 105, has ten arches with a central height of 70 feet. These viadncts call for no special description, being similar to those that have gone before in this paper. Coombe viaduct is an example of arches of 569 feet span. This was the farthest point

Downloaded from pme.sagepub.com at WEST VIRGINA UNIV on June 5, 2016 JULY1899. RAILWAY VIADUCTS IN COBNWALL. 36 I: westward to which the stone from the quarry near Doublebois mas. carried. The last viaduct ordered by the Oornwall Bailway Company waa Ooombe-by-Saltash, Plates PO6 and 107. It was built by contract, the contract being signea in 1889, after the line hdbeen taken over by the Great Western Bailway Company. It is sitnated close to the Baltash station, and carries the railway across a tidal creek where mu& to a depth of about 45 feet is found. The foundations being costly, a span of 90 feet was adopted for the arches, which are seven in number, while the central height is 86 feet above the surface of the mud. Timber cofferdams were used for the three piers in the tidal estuary, and a good rock foundation was obtained throughout. Between the years 1883 and 1889 the Great Western ]Railway Co., who owned the West Oornwall line between Truro and Peneance, reconstructed seven viaducts on that section of their system. Between Truro and Chacewater stations three were built with granite masonry, with arches of 45 feet span and 15 feet rim- Penwithers, Fig. 28, Plate 105, has seven arches with a central height of 68 feet; Chacewater has five arches with a central height ~f 55 feet; Blackwater has seven arches with a central height of 70 feet. The drawing of Penwithers will suffice to illustrate all the viaducts of this class. Bedruth viaduct, close to the station of that name, is also built. with granite masonry, and has seven arches of 564 feet span and rise ~f 20 feet; and one of 60 feet span over Penryn Street. This viaduct was built in two sections throughout, for here as at Bolitho Back of land required the site of the old viaduct to be dtimately occupied by the new work. Piers as well as arches were put up at two operations, and without any perceptible indications remaining to show the line of junction. Angarrack. viaduct, between Bwinear Bod and Hayb stations, is also of granite ; it has eleven arches of 566 feet span with n rise of 2Q feet, and it crosses a broad valley at a height of about 100 feet. A photograph, Fig. 26, Plate 104, of this viaduct shows it when nearly completed. Half a mile nearer Hayle, Buildford viaduct will be found. It has arches of the smaller size, 45 feet with a rise

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~f 15 feet. They are six in number, with a central height of 53 feet. The drawing of Penwithers, Fig. 28, Plate 105, suffices to illustrate &is type of work. All these were built by contract. Adjoining Hayle Station is a long low viaduct with thirty-six spans of about 20 feet each, and two spans of 40 feet. In reconstruction the axis of the old viaduct was retained; new piers were built and old ones enlarged ; and the timber Superstructure was replaced bit by bit with one of wrought iron. The erection Qf the new superstructure waa done by the Company’s staff, while the rat of the work was let by contract. Following the amalgamation of the Cornwall with the Company, the narrowing of gauge works ensued in 1892, and soon afterwards the work of viaduct reconstruction in Cornwall, in connection with the doubling of certain sections of the line, was undertaken on a large scale. The general lines of the earlier reconstruction were not changed--that is to say, where the height of the old viaducts and the piers admitted it, new steel superstructures were erected on the original piers, which were raised for the purpose. Examples of this are to be seen at Liskeard viaduct, close to the station; at Coldrenick viaduct close to Menheniot station. The method of erection on the original axis and without interruption of traffic was the same as has been described in the case of Xt. Pinnuck and of Largin viaducts ; but instead of the Barlow rail decking formerly used, corrugated steel flooring is mpplied ; and the piers are raised with Staffordshire bricks instead of with stone masonry. Liskeard viaduct is illustrated by Fig. 29, Plate 105, which shows old and new work. At Keyham viaduct, Plate 108, near Devonport station, the process of reconstructing in steel on the old piers raised is now in progress. EPere it has been necessary to widen some of the piers from the foundations; in the former instances the new masonry .or brickwork begins at about 35 feet below level of rails. The form of the old piers at Eeyham is not so suitable as in those at Liskeard and elsewhere. In all these viaducts erected on same site as that of the running lines, the girder work is provided by contract, but all the rest is done by the company’s staff.

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New viaducts in granite masonry, with arches differing but little €rom those idready described, have been built at Treviddo and Tsesulgan, one on each side of Menheniot station ; these have only been lately opened for traffic, and at Tresulgan the old viaduct has not yet been removed. At Milltown, near , a viaduct Pike that at Treviddo was completed in 1895. Two large viaducts of similar character have recently been completed near St. Austell. Gover viaduct has eight arches with a central height of 99 feet, 8t. AustePl viaduct, Fig. 9, Plate 96, has ten arches with a centraL height of 115 feet. Arched viaducts in granite masonry not yet completed or open for traffic are situated thus :-Tregarne, between Grampound Boad. and Truro ; Tregagle, between Grampound and Truro ; Penponds,. one mine below Oamborne station. A11 these masonry .iiaducts are being built by contract; they have the main arches turned with 8taffordshire bricks, and the parapet walls, and in some cases the spandril walls, are also of the same material. Plates 103 and 106 illustrate the type of design adopted in these of current date. The foundation generally obtained throughout the series has been shale rock, the beds being inclined at various angles, between the horizontal and vertical; and no single case of settlement due tu- failure in a foundation to carry its load has arisen, from the beginning of the reconstruction work up to the present time. From ten to fifteen feet of excavation has generally sufficed to reltcb the rock ; in a few cases the depth has been twice as great. Timber centering has been used, several viaducts in succession being served by the same centres. American yellow pine is the timber used generally in the Cornwall viaducts, and the preserving process is that known as kyanizing. This process has been found to render the timber not liable to catch fire easily, and this is a very necessary qualification in preparing timber €or such purpose and situation.

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Discussion. The PRESIDENTasked the members to accord a vote of thanks to RIP.Gibbons for his kindness in preparing the very interesting account of works of great variety, involving very large responsibility, which he believed, had fallen upon the author. By the invitation of Nr. Gibbons and the Great Wesfern Railway Company, members who wished to do so would be able to see some of the representative viaducts and bridges described in the Paper. He remembered the floating of the first section of the ]Royal Albert Bridge. In their ignorance they were accustomed to think that the free use of timber on the viaducts in Cornwall had some connection with the necessarily great cost of the Albert Bridge ; but whatever might be true in that respect there was no doubt that those who had to undertake the maintenance and development of the Cornish lines were now putting upon them work of an entirely different character from that which had been originally done.

Mr. GIBBONSsaid he had nothing particular to add to the substance of his Paper, and thanked the members for the cordial way in which the President’s kind remarks had been received. He had a considerable number of photographs which he would lay on the table if any gentleman would like to look at them, because they illustrated the more recent construction that bad been going on. A glance at the photographs of the works would speak a great deal more clearly to members, whose time was short and who had only a limited opportunity of looking over the great area covered by the works, than any remarks he could make. Any gentlemen who were able to go to the Royal Albert Bridge 01 to the TVest$#n Nil1 viaducts would be heartily welcomed by members of the Great Western Railway staff.

Downloaded from pme.sagepub.com at WEST VIRGINA UNIV on June 5, 2016 Downloaded from pme.sagepub.com at WEST VIRGINA UNIV on June 5, 2016 RAILWAY VIADUCTS. Plate 93.

Fig. I. St. Gevpnnns Vinduct. Class A.

See Details Plnte 94.

Fig. 2. Tvuro Viatlmt on the Ma& Lipie. Class B.

Fig. 3. Ponsnnooth Viaduct OH the FalnlozLtll Braiich. Class B

See Dctclils Plate 95.

Meclinnicnl Eiigineers 1899 ? 100 0 700 200 300 400 500 600 700 800 900 Feet. 6 DownloadedLLULLLYl from pme.sagepub.com at WEST VIRGINA UNIV on June, 5, 2016 I. 1- RAILWAY VIADUCTS. Pltrte 94. St. Gevrniins Viaduct, still in use. Fig. 4. Clnss A. Fig. 5.

Downloaded from pme.sagepub.com at WEST VIRGINA UNIV on June 5, 2016 HAILWAY VIADUCTS. Plate 95.

I

Poulsnllootk viclduct. Class B.

For geenerd view See Fig. 3.

I

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St. Austell Viaduct. Class R.

Fig. 8. Now taken down.

Fig. 9. New Work in progress.

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Fig-. 10. Gover Viaduct, iiow removed. Clnss B.

233 ynvtis long. 95 feet central height.

Downloaded from pme.sagepub.com at WEST VIRGINA UNIV on June 5, 2016 Meclian ical E ngi xeew 1899. RAILWAY VIADUCTS. Pltrte 98.

Fig. 11. Royal Albert Bvidge at Snltnsli. Opened 1859. Evecting one of the Main Tubes.

Oz'til tubes 17 feet x 12 fiet. Avclies 445 feet wide. Height 100 feet above high wuter. Lerigtli iieavly half-a-inile. Downloaded fromMechunicd pme.sagepub.com atEngipieers WEST VIRGINA UNIV1899. on June 5, 2016 RAILWAY VIADUCTS. Plate 99. 'C Dvawwood Etribaiikntent. Sample Middl,: Arch of 26 Arches. i

Fig. 12. Fig. 14. Section of B uttvess. No. 13.

- .------

------t c- 71 Fig. 13,

Feet 10 Downloaded5 from pme.sagepub.com0 at WEST VIRGINA10 UNIV on June 5, 2016 20 Feet I IIIJ,,.,I I I I Fig. 15,

For general view See Fig. 18.

Fig. 16.

Downloaded from pme.sagepub.com at WEST VIRGINA UNIV on June 5, 2016 RAILWAY VIADUCTS. Plate 101. Fig. 17. West L(iugi7L Vimlmt. Thee Auches.

See Details, Figs. 15 tritd 16. I’ltrte 100.

Fig. 19. Cliiitzick Vindz6ct.

7.5 feet to aii inch. Fig. 20. Mnorswnter Viuduct. Eight Arches. j See Plates 102 aiid 103.

100 fect to nn iitclr.

Downloaded from pme.sagepub.com at WEST VIRGINA UNIV on June 5, 2016 Mech (i~ical E ngitt eeus 1899. RAILWAY VIADUCTS. Plate 102.

Moorswater Viaduct. April, 1879.

Fig. 21.

Fig. 22.

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Fig. 24.

DownloadedMeclraiiical from pme.sagepub.com Engineers at WEST VIRGINA 1699.UNIV on June 5, 2016 RAILWAY VIADUCTS. Plate 104.

Fig. 25. St. Pitmock ViadzLct, conipleted 1886'.

Fig. 26. Aqavvack Viadzict, coriipleted 188iT.

DownloadedAileclicinicnl from pme.sagepub.com Engineevs at WEST VIRGINA 1899. UNIV on June 5, 2016 RAILWAY VIADUCTS. Plate 105. Fig. 27. Cooiiibe (St. Steplien's) Viaduct.

Pepi 20 ithe~s Viaduct.

100 feet to ail ziich. Liskeni d Vzaduct, Old niid New. Mechamcnl Enpseers 18.99.

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Coonibe-by-Saltash Viaduct.

Fig. 30. New Wovks iir progress.

Fig. 31. Arches 70 feet spm, 25 feet vise.

Downloaded Mechriiriculfrom pme.sagepub.com Engineers at WEST VIRGINA UNIV1899. on June 5, 2016 Plnte 107.

Downloaded from pme.sagepub.com at WEST VIRGINA UNIV on June 5, 2016 RAILWAY VIADUCTS. Pliite 108, A'eyhi~ti Vi(idmt, 19th February, 189.9, Slro-wiiig old stone tirid izezu Brick exterrsion of piers, old zuootleii trusses, and Iiezci iroii girders. Fig. 33. Iron Girder shg.

Fig. 34. Girdev fixed.

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