1806 John Grieve’s Tunnel

In November 1805 a small group of mining engineers explored the idea of a tunnel under the Forth.
John Grieve published their proposal in John Grieve’s 1896 Report

The notion was based on observations of existing coal mines especially those at Bo’ness and Whitehaven in Cumbria, where the seams were successfully mined under the Forth and Irish Sea respectively from tunnels that extended a mile or more under the bed of the river / sea respectively.

They noted:

“At Bo’ness they have carried their coal workings under the Forth for a mile without experiencing any inconvenience with workings from 20 to 80 fathoms below high-water mark

At Whitehaven (in Cumbria) they now work coal for about the same distance under the Irish Sea, and at both places, less water is met in the workings under the sea than in workings under land

At Whitehaven, men and horses go from the earth’s surface into the colliery every morning, and return every evening. This, considering the great depth as well as the length of it, is a far harder journey than crossing and re-crossing by the Tunnel at Rosyth would be; and yet that journey the men and horses at Whitehaven perform daily, besides performing their usual day’s work.”

Route of the Tunnel

At first one is led, in this investigation to Queensferry where the breadth is only one mile. But we soon are obliged to abandon this place because a) the rock is whinstone for more than half-way across, and mining would be enormously expensive and b) the depth of tide is no less than 36 fathoms. Beamer marks the west edge of the whinstone band.

Further west is a band of limestone that runs across the river from about Rosyth Castle. Miners dislike limestone generally, and this band includes good and bad parts which are almost as hard to work as whinstone. Dhu Craig marks the east edge of the limestone.
Between these two is a band of free-stone and “passable metals” – these are desirable metals for cutting a tunnel.

[Freestone, so named because it can be freely cut in any direction, must be fine-grained, uniform and soft enough to be cut easily without shattering or splitting. It is used for moulding, tracery and other details that need to be worked with a chisel.]

The deepest part of the Forth between Rosyth and the opposite shore is about 12 fathoms Of course the proposed tunnel must go deeper, how much will be determined by probing the deepest part with boring rods. It will probably not be more than 20 fathoms below high-water mark.

An extract from John Grieve’s plan showing the planned route of the tunnel

Grieve originally proposed that the tunnel would start on the surface and slope down to achieve sufficient depth before turning toward the river. On the north the tunnel would start a little way inland, and curve round and down before taking the direct straight-line route a, b, c. On the south, the tunnel would turn more sharply then running parallel to the shore would slope upwards to emerge about Linn Mill.

The Earl of Hopetoun was expected to object to this route so the a, b, d slightly longer route was proposed as an alternative or even the d, e, f route.

The total length of the tunnel underwater was reckoned to be about 2 miles or 1800 fathoms (a fathom is 6ft)

Cross-section of the tunnels

The plan assumed two-way traffic would run in a single wide tunnel where possible, using parallel tunnels at any places where the rock was less suitable for supporting a broad tunnel.

Digging the Tunnel

The proposal was to sink two vertical “moated” shafts at the low-water mark on each shore on the line pf teh tunnel. The “moat” would be a caisson to keep water out of the shaft at high tide.

The low-water mark is about half a mile out from both shores, so about halfway to the middle of the tunnel.
From the bottom of each of these vertical shafts, tunnelling would proceed north and south simultaneously. Assuming a tunnelling rate at any given face of two fathoms per week, the overall tunnelling rate would be eight fathoms per week – two separate directions at each end simultaneously, so 1800 fathoms would take 1800 / 8 = 225 weeks or about 4½ years.

Draining the tunnel

Cross section of parallel tunnel showing the drainage tunnel beneath”

As well as the main tunnel, a small drainage tunnel ran beneath the roadways and would be pumped dry from the north end.

Mechanisation

“Objections to the smoke from steam engines are likely from the Earl of Hopetoun. However a late improvement in the furnaces of steam engines means that they burn their own smoke rendering a steam engine a much less obnoxious neighbour than formerly. The steam engine of the south side would only be required during construction, once the tunnel is complete pumped drainage would be from the north side. If the steam engine should be deemed inadmissible, other machinery can be substituted, although at some disadvantage.”

Costing the tunnel

The Business Case

No one had built a road tunnel before, so they looked at other examples of places where communications had been improved especially the Wearmouth Bridge at Sunderland,

The Wearmount Bridge 1796 was the second major bridge to be made from cast iron.

The bridge was built alongside an existing ferry crossing and over the next ten years the revenues of both the bridge and the ferry increased steadily.

Grieve and his colleagues believed that the same thing would happen with their Tunnel, improved communication would generate more traffic

“An increased intercourse with all the town north of the Forth would be a sure consequence. Every town, to the south, has enjoyed a regular communication with capital by stage coaches, or other conveyances, whereas, the mail-coach excepted, nothing of the kind crosses the Forth. This accommodation would then be afforded to these populous and numerous northern towns; and would form no inconsiderable source of revenue. Sn agricultural intercourse, altogether new, betwixt that rich district to the west of Fife and the city of Edinburgh, equally beneficial to both, and beneficial also to the Tunnel, would follow. The more ready access to the city opened up to the noblemen and gentlemen and their families, resident north of the river, would also increase their intercourse and prove beneficial. A proportion of travellers by Stirling Bridge, and a proportion, perhaps not small, of both travellers and carriage by the Ferry at Kinghorn, would accrue to the Tunnel. The legislature also, in the military arrangements, would have frequent recourse to the Tunnel, and would afford an emolument by no means trifling. In short, the increase of every species of intercourse is certain, and certainly affords the prospect of a fair return for the capital sunk in the adventure.

The fate of the scheme

The tunnel never did get started because it failed to attract sufficient finance.

British Geological Survey of the Forth

it would have run into difficulties, because although the freestone bed does continue beneath the Forth, there is a great chasm in the river bed – caused by the glacial scraping activity in successive ice-ages. A bored tunnel would have been possible, but only at a much greater depth and the additional cost would have made it unviable.

The situation at Queensferry

Grieve’s report had noted:

The post chaises kept upon both sides which are well employed, and none of which pass the ferry, would all pass the Tunnels; and would bear a very considerable proportion to the present receipts. Travellers also upon horseback, who generally are obliged to stop, and are often long detained, and must spend money at the inns upon both sides, would willingly pay a higher fare to be delivered from this evil. The same rule will apply to cattle; and the increased number of them it would be impossible to calculate.

Grieve and his colleagues were not alone in noting these issues, complaints about the ferry service were widespread and in 1809, the government declared “the irregularity of the service and the want of any control over the conduct of the boatmen at the Queensferry Passage (the great line of communication to the north of Scotland) made it necessary to take measures for its regulation and improvement.”

The era of private boatmen ended in 1809 with an Act of Parliament which brought the ferry into a public-private partnership. The government matched the capital raised by private investors who the benefited from a share of the revenues generated by ferry fees.