The South Approach Railway.
This line has a total length of 58 chains, and passes through a cutting about 20 ft. on the average in depth, through soil and clay, and strata of freestone, intermixed with coal and shale.
At about 10 chains from the bridge the new Forth Bridge Station is situated. At 45 chains the line to Winchburgh branches off to the west with a sharp curve.
The building of the Forth Bridge Station, and the widening of cutting, bridges, and embankments not at first contemplated, will bring up the total cost to about 20,000l. The contract will probably not be finished until the end of April.
The North Approach Railway.
This line is nearly two miles in length, and commences with an embankment at the north end of the bridge. The embankment is 34 ft. in depth at the abutment of the masonry arches, and continues for a length of 14 chains, when cutting No. 1 commences. This cutting is through whinstone, and is over 600 yards long, with an average height of 80 ft. The work here was commenced by driving a toplift from both ends at about 40 ft. above formations, and at the same time bottom gullets from the south end and the north end. The material excavated was run down an incline, worked by gravity in the ordinary way, and deposited to form No. 2 bank. The excavation made in the top-lift proved the rock to be of such a nature that an open cutting at the great depth would not have been compatible with safety to the traffic, and it was decided to form a covered way for the portions already excavated and to tunnel the remainder. Accordingly, shafts were sunk in two places, and headings were driven from them in each direction. The tunnelled portions are lined with side walls of roughly dressed whinstone and rubble backing, while the roof is of brick. The covered way has side walls and roof both of whinstone masonry. Starting from the south end of this cutting there are 189 yards of covered way, 229 yards of tunnel, and 154 yards of covered way, at the end of which the cutting terminates and bank No. 2 commences. This is 11 chains in length, and is followed by a cutting through whinstone 11 chains in length and, on the average, 50 ft. in depth. Another embankment follows, gradually deepening and leading to a viaduct crossing the North British Railway and the public high road, and by another bank the outskirts of Inverkeithing are reached.
The viaduct consists of masonry abutments in the form of eliptical arches of 57 ft. span at either end and four spans of steel girders of 100 ft. span each. The girders rest on masonry piers set at an angle of 25 deg. to the centre line, and the whole viaduct is on a curve of 40 chains radius with a gradient of 1 in 70.
At the north abutment of this viaduct the bank is 85 ft. in height, but, situated on rising ground, rapidly falls away.
At 11⁄2 miles from starting another cutting through whinstone commences, this extending for 6 chains, followed by a tunnel 378 yards in length under the town of Inverkeithing. Finally the line terminates in a junction with the North British Railway at Inverkeithing.
The last-mentioned tunnel is also on a curve of 40 chains radius with a gradient of 1 in 70, and was excavated by means of headings driven from each end. The enlargement to full size was principally made from the south end of the tunnel, as the material was required at that end for the filling up of the banks. This tunnel is lined with masonry side walls, and a brick roof.
Apart from the heavy cutting and tunnelling work, the greatest difficulty in this contract was caused by a bog through which bank No. 2 had to be carried. After some quantity of spoil had been tipped from the north end of No. 1 cutting, the weight of this material commenced to force up the ground in front, and this to such an extent as to displace the public high-road running to the south west side of the bank, carrying this road some 60 ft. out of its course and altering the gradients materially. There was at one time a fear that it would displace the North British Railway line between North Queensferry and Inverkeithing as well, but fortunately it stopped short of this. There is in this bank an excess of 69,000 cubic yards over and above the estimated quantity of 115,000 cubic yards, and to obtain the necessary quantity of spoil the east side of No. 2 cutting was enlarged to the necessary extent.
Geologists will have it that this is the site of an extinct volcano, but it will probably be best to leave this question to be settled by geologists.
In the excavation of tunnels and cutting, pneumatic drills were generally used with good results. The explosives used were both dynamite and ordinary blasting powder.
The total rock excavation amounted to 341,500 cubic yards in the solid.
The filling in the banks is as follows:
| Bank No. 1 | 33,400 | cubic yards. | |
| No. 2 | 115,600 | " | (original estimate) |
| " | 69,000 | " | (excess) |
| No. 3 | 198,100 | " | |
| Masonry | 24,850 | " | |
| Ballast | 13,350 | " | |
| Filling | 1,000 | " | |
| Total | 455,300 | cubic yards. |
The total weight of steelwork in the viaduct and road bridges is 460 tons for the former and 190 tons for the latter—total, 650 tons.
The whole north approach line, from the abutment of the bridge to Inverkeithing, is on a gradient of 1 in 70, except at one point, where it is level for about 100 yards.
The sum for this contract was 88,678l., increased through extra work by 18,000l., or a total of 106,6782l.—equal to something over 56,000l. per mile.
A new station has been built at Inverkeithing. At present there is no station between this and the Forth Bridge Station on the south side.
The writer wishes to express his indebtedness to Mr. Louis Neville, the contractors' engineer for the approach railways, who furnished the above particulars.
Weight of the Superstructure.
The subjoined tabular statement will give some idea of the amount of steel distributed over the main supports.
| Description of Parts. | Fife. | Inchgarvie. | Queensferry. | Total. | |||||||||
| Tons | Cwt. | Tons | Cwt. | Tons | Cwt. | Tons | Cwt. | ||||||
| 3 Central towers, including bedplates | … | 4815 | 16 | 7036 | 4815 | 16 | 16,667 | 12 | |||||
| 6 Cantilevers | … | … | … | … | 1 fixed 1 free | 2 free | 1 fixed 1 free | ||||||
| Bay 1 | … | … | … | … | … | 4235 | 4 | 4312 | 12 | 4235 | 4 | 12,783 | |
| " 2 | … | … | … | … | … | 2626 | 2 | 2658 | 12 | 2626 | 2 | 7910 | 16 |
| " 3 | … | … | … | … | … | 1764 | 6 | 1724 | 16 | 1764 | 6 | 5253 | 8 |
| " 4 | … | … | … | … | … | 1034 | 3 | 1009 | 16 | 1034 | 3 | 3078 | 2 |
| " 5 | … | … | … | … | … | 665 | 18 | 620 | 4 | 665 | 18 | 1952 | |
| " 6 | … | … | … | … | … | 490 | 2 | 423 | 12 | 490 | 2 | 1403 | 16 |
| 2 Central girders | … | … | … | … | 410 | 15 | 821 | 10 | 410 | 15 | 1643 | ||
| Rocking-posts and steel castings | … | … | 51 | 9 | 51 | 9 | 51 | 9 | 154 | 7 | |||
| Ladders in tubular members | … | … | 36 | 40 | 36 | 112 | |||||||
| Totals | … | … | 16,129 | 15 | 18,698 | 11 | 16,129 | 15 | 50,958 | 1 | |||
| Weight of a | fixed cantilever: 5441 tons. |
| "" | free cantilever: 5375 tons. |
| "" | 1710 ft. span: 11,571 tons 10 cwt. |
| "" | cantilever bridge per foot run: 9 tons 11 cwt. |
Table No. XII. on the next page shows the quantities of steel erected and bolted up and rivetted during the years 1887, 1888, and 1889, month by month. These quantities apply to the three main piers of the cantilever bridge only.
The total cost of the foundations of the Forth Bridge may be roughly put down as nearing 800,000l; and in connection with this expenditure it is necessary to mention the name of Mr. P. W. Meik, who acted as resident engineer for, and as representative of, Messrs. Sir John Fowler and Baker from the commencement in 1883 until the completion of the masonry piers in 1886, and of whose unfailing tact and courtesy his many friends retain the liveliest remembrance.
Another name should be added here, that of Mr. William Gray, who from start to finish had charge of all excavation and masonry work, besides other duties of the most multifarious character, and of whom it may be truly said that, day or night, early or late, no one would ever call upon him and find him unwilling to do what was wanted.
The total expenditure by the Forth Bridge Company upon construction has been as follows. The figures are approximate amounts as far as expenditure year by year is concerned, but the total amounts are correct and authentic.
| For half-year ending | ||
| These amounts include the expenditure for the construction of the north and south approach railways, but nothing for the connecting line. | ₤ | |
| December 31, 1882 | 7000 | |
| June 30, 1883 | 42,800 | |
| December 31, 1883 | 57,000 | |
| June 30, 1884 | 119,000 | |
| December 31, 1884 | 218,200 | |
| June 30, 1885 | 231,000 | |
| December 31, 1885 | 216,000 | |
| June 30, 1886 | 188,000 | |
| December 31, 1886 | 253,500 | |
| June 30, 1887 | 240,000 | |
| December 31, 1887 | 243,000 | |
| June 30, 1888 | 195,700 | |
| December 31, 1888 | 218,000 | |
| June 30, 1889 | 182,000 | |
| December 31, 1889 | 138,000 | |
| Total…… | 2,519,200 | |
| Add to this the amount expended in connection with Sir Thomas Bouch's suspension bridge (including all parliamentary expenses) | 250,000 | |
| 2,799,200 | ||
| Parliamentary expenses in connection with cantilever bridge, engineering expenses, interest during construction, &c. | 378,006 | |
| Total expenditure to January 1, 1890 | 3,177,206 | |
It is estimated that a further sum of 50,000l. will be required to complete the structure, the painting included.
The sale of plant is expected to realise fully 120,000l.
For the erection alone of the Fife, Inchgarvie, and Queensferry Piers, that is, everything on top of the circular granite piers which may be strictly called the superstructure, the amount of wages paid including salaries of officials in charge of the piers, amounted up to November 30, 1889, to a total sum of 344,810l; the total amount of steel put up and rivetted up to that date being 50,064 tons. The cost of labour for that work is therefore 62. 17s. 9d. per ton erected and rivetted up.
The total amount of wages and salaries paid on the works up to January 1, 1890, was 1,045,000l.
The Forth Bridge Railway Company.
The agreements between the four companies which guarantee the interest on capital, provide that the directorate of the Forth Bridge Railway Company should consist of the chairman and vice-chairman of each of the four interested companies, and of two directors elected by the general body of shareholders. The chair of the Forth Bridge directorate is held in rotation by the four chairmen of the guaranteeing companies, the term of office being twelve months. The representation at present is as follows:—
Mr. M. W. Thompson, chairman, and Mr. W. Unwin Heygate, Midland Railway Company.
Lord Colville, of Culross, and Lord Hindlip, Great Northern Railway Company.
Mr. John Dent-Dent, deputy chairman, and Sir Matthew White Ridley, Bart., North-Eastern Railway Company.
The Marquis of Tweeddale and the Earl of Elgin and Kincardine, North British Railway Company.
