354 



NA TURE 



{^Attgust II, 1887 



over the works and piers ; and telephonic communication was 

 established between the offices and all the centres of operations. 

 The workshops and yards were rapidly completed, and furnished 

 with tools, of which many are of a special and novel description. 

 Ever since the commencement the work has progressed with- 

 out interruption, and has gradually assumed the gigantic propor- 

 tions of the present time. Over 3000 hands have been employed 

 continuously for the last year ; and during the present summer 

 months the number has been increased to 3600. The majority 

 find lodgings in the neighbourhood of the bridge ; and the 

 remainder make use of a special train service to and from 

 Edinburgh, and a steamer to and from Leith, put on for their 

 use night and morning. 



Materials. — The materials for the permanent work have been 

 obtained throughout from producers of repute : Aberdeen 

 granite from Messrs. Fyfe ; Portland cement from Messrs. 

 Hilton and Anderson and Bazley White ; Siemens steel from 

 the Steel Company of Scotland and the Landore Steel Works. 

 All the steel has been subjected to rigid examination, and has 

 passed the ordeal of specified tests before leaving the niakers' 

 works ; a few specimens showing its high quality are exhibited. 

 The materials delivered up to the present time have in- 

 cluded — 



Granite 

 Portland cement 



The amount thus far erected has been — 



Masonry in piers and abutments ... 

 Steel in approaches and main spans 

 Steel for main spans, prepared ready 

 for erection, about 



550,000 cubic feet. 

 21,000 tons. 



129,500 cubic yards 

 19,000 tons. 



20,000 tons. 



By the time the first consignment of steel arrived, the shops 

 were ready for the preparatory operations, and the whole 

 establishment was rapidly organized to deal in the most complete 

 manner with the work to be executed. Hydraulic power is 

 freely used, from the extremely neat form of shop crane to the 

 2000-ton press for curving the tube-plates. With the exception 

 of the main-pier caissons, made by Messrs. Arrol Brothers of 

 Glasgow, and the superstructure of the approach spans by 

 Messrs. P. and W. Maclellan of Glasgow, the whole of the 

 work has been turned out of the shops at the bridge, their 

 present capacity being an output of 1300 tons of finished work 

 per month. 



Shop Practice. — The procedure in the shops may be described 

 as follows. The flat plates and bars are first straightened. The 

 plates to be curved are heated to a uniform red heat in a gas 

 furnace, and while red-hot are moulded in dies under hydraulic 

 pressure to the required form, stacked and coated with ashes, 

 and allowed to cool slowly and equally ; any subsequent warping 

 is taken out by placing them again in the press when cold, and 

 giving them a final squeeze into the correct shape. The butts 

 of the bars are cold sawn, and the edges and butts of the flat 

 plates are planed in the usual manner. The ends of the curved 

 plates are planed in a novel form of machine, in which the tool 

 travels in a circular path readily adjusted to the radius of the 

 curved plate. On completion of the planing, the plates are 

 taken to the tube yard, and are built up round the longitudinal 

 ribs and internal stiffening frames, which have previously been 

 fitted together in moulds to the exact diameter required : so 

 that the plating of the framing at once gives the tube its proper 

 form. The plates are in i6-feet lengths, and break joint alter- 

 nately over the stiffeners at 8-feet intervals. Means are adopted 

 to keep the tubes in line while the rivet holes are pierced by a 

 travelling annular drilling frame, which is mounted on wheels 

 and carries a boiler and engine driving ten drills by cotton ropes. 

 A pair of drills are attached to each bed ; and as the beds can 

 traverse the circumference of the tubes, while the drills can 

 traverse the length of the beds, the whole outside of the tube is 

 commanded, and the holes are completed with accuracy to 

 insure their precise coincidence when the parts are rebuilt at the 

 site. _ As fast as each section of 8 feet length is finished, the 

 machines are propelled along the rails to take up a new position ; 

 they thus travel gradually in successive stages over the whole 

 length laid down. The tee and trough-shaped parts are built 

 together in the shops, and the holes are drilled by adjustable 

 vertical and horizontal drills, fitted to a travelling carriage ; the 

 power is transmitted to the machines by ropes from the shop 

 shafting. Numerous radial machines are also in use for the 



Secondary parts. For dealing with special parts, many ingenious 

 and somewhat novel workshop appliances have from lime to time 

 been brought into use, beyond those here mentioned. All the 

 parts of the junctions are carefully fitted together in the yard in 

 the exact positions they will relatively occupy in the bridge. 

 After each member has been prepared, the pieces are painted, 

 marked, and stored until required for erection. 



Founding Piers. — With the founding of the piers below 

 water commenced the more difficult part of the undertaking ; but 

 without any sensible delay the whole of the piers have been suc- 

 cessfully sunk and completed. The foundations for piers in 

 shallow water were put in either by tidal work or by open coffisr- 

 dams, and the excavation was carried down to boulder clay 

 or rock. Though these were of individual interest themselves, 

 from the size and difficulties met with, they are dwarfed by the 

 magnitude of the operations connected with the deep-water 

 piers, of which those in the south group are embedded in the 

 boulder clay in one case at 90 feet below mean water-level, while 

 at Inchgarvie they rest on a level bench cut out of the sloping 

 whinstone rock at a depth of 72 feet. 



Caissons. — The caissons for all the deep piers are 70 feet in 

 diameter at base ; the cutting edges and shoe are of steel, and 

 the upper parts of wrought-iron. They were first built on ways 

 on the south shore, and were launched with sufficient ballast on 

 board in the form of concrete to insure their stability while 

 towed out to their berths at the end of the jetties, where guide 

 piles and dolphins were used to place them in correct position. 

 Temporary wrought-iron cofferdams were built upon the top of 

 the caissons, timber working decks constructed, cranes and con- 

 crete mixers fixed, air-pressure connexions made good, and 

 sinking operations commenced with a pressure in the excavating 

 chamber sufficient to drive out the water; the air compressing 

 machinery was placed on the jetty alongside. The Inchgarvie 

 caissons'had to be equipped with all these fittings while moored to 

 the south jetty, so as to be ready for work on arrival over their 

 rocky bed. 



The working chamber was illuminated by electric lights ; and 

 communication was effiacted with it through three shafts with 

 air locks on the level of the upper deck. The two shafts for the 

 skips bringing up the excavated material were constructed with 

 horizontal sliding shutters, worked by hydraulic rams, in place 

 of the usual swing doors. The winding drum for bringing up 

 the skip from the working chamber was not in the lock itself, but 

 driven by an engine outside. On arrival of the skip in the lock, 

 the lower slide was shut to, and the blow-off cock opened for 

 releasing the pressure, the top slide drawn back, and the hook 

 of the discharging crane was coupled to the skip by hand. This 

 direct and rapid method of transit for the excavated materials 

 greatly facilitated the sinking ; the whole operation from arrival 

 of the skip in the lock to its removal lasted only about three- 

 quarters of a minute in ordinary working, the sequence of the 

 movements being automatically controlled by interlocking gear. 

 The air locks in the third shaft for the men were constructed with 

 a view of rapidly changing shifts, and had double chambers, each 

 capable of holding seven men. 



The silt overlying the harder deposit was expeditiously expelled 

 from the working chamber by means of ejection pipes passing 

 into water outside, the air-pressure being sufficient to blow out 

 charges of silt and water mixed in a box which communicated by 

 a valve with the ejection pipes. On reaching the boulder clay, 

 ]3ortable steel diggers, actuated by hydraulic cylinders placed 

 between the roof and the implements, were brought into use to 

 break up this hard material. 



At Inchgarvie a modification of this system was required for 

 sinking the deep piers into the hard whinstone rock, which had a 

 natural slope of i in 4|. Bags of sand and concrete were de- 

 posited in two piles on the deeper side of the site to be occupied 

 by the caisson, which had been launched with massive timber 

 blocks in the chamber, to rest upon this artificial bed ; these 

 blocks and the edge of the caisson touching the rock on the 

 shallower side were the first bearings it took when lowered at the 

 site. The whole of these primary operations required extreme 

 care to provide for differences of weight on the base, due to the 

 depth of water at different states of the tide. Then by means of 

 rock drills and ordinary quarrying operations inside the air- 

 chamber the rock was excavated until the caisson was sunk to a 

 level bench cut out of the sloping rock. In these caissons the 

 full pressure of air due to the head of water was maintained 

 during the sinking, and it was found advisable to change tb 

 gangs every four hours ; the maximum pressure reached at hif 



