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British tunnelling: a short history

TECHNICAL NOTE

The origins of tunnel construction probably lie in coal and mineral mining, where surface deposits soon became exhausted and miners began to venture underground, first with open holes and then, after many collapses, using timber supports.

These headings, which eventually reached many kilometres underground, were skilfully built, as safe passage in and out for both labour and materials relied on sound construction.

Passing bays were needed and these were simply enlargements made in the sides of the tunnels. Consequently, bigger spans became necessary and with these grew knowledge of supports and supporting materials.

The Romans mined tin, copper and gold in Britain, but it was coal that became the lifeblood of industrial development and in 1777 James Brindley brought the expertise of coal mining and tunnelling together for the Duke of Bridgewater, building a tunnel for his mine at Worsley in what is now Greater Manchester. This tunnel was to bring coal directly form the Duke's mines to the industrial centres in Yorkshire and the Midlands, where the pottery and later the steel industries required huge quantities of coal.

The race was on to deliver faster and bigger loads, far more than could be carried by the poorly built and badly neglected cart-track roads. Canals and consequently tunnels became big business and attracted many eminent engineers such as Telford, Rennie, Locke and Outram.

Surveying was a main feature of canal design and levelling skills were probably the most important, as contouring around hillsides was thought to be the best option for canal operation.

But where contouring was not possible, locks or tunnels were needed to negotiate obstructions and levelling allowed engineers to identify the best start points for both methods.

Knowing the possible position that the canal could finish from the levels, the engineer used the best available means, generally a horse and length of rope, to identify the best line for the tunnel or lock system, by letting the horse pull the rope from start to finish and then pulling the rope as tight as possible.

The line of the canal was then marked and tunnel shaft or lock positions determined. Borings (later used as shafts) were then sunk to determine the ground conditions.

Locks were expensive to build and created bottlenecks in the system and often lost water. They also required a source of water at the topmost lock otherwise the water would drain without being replenished and the system would be useless or at best very intermittent.

Tunnels were even more expensive, although they kept the canal system moving, even when they were only one way. Canals wide enough to allow two boats to pass relieved the bottlenecks that Telford found in the Birmingham area where boats were often stationary for several weeks waiting to pass through narrow tunnels.

Even though strict timetables were kept for movements through tunnels, clocks were rare and pressures were great on the tunnel and lockkeepers to bend the rules. There were often races to reach the centre of the tunnel to see which boat had to go back having failed to reach the centre first.

Larger tunnels were needed but these were significant undertakings with large spans that needed support, particularly in poor ground conditions, as not all tunnels could be built in rock.

Even in solid rock the risk of rock fall was significant when weathering and atmospheric softening began to loosen the structure. Rock shields were common rather than full linings and these were built across the tunnels rather like bridge decks.

The last brick canal tunnel to be built in Britain was the Netherton Canal tunnel near Birmingham in 1858 and this was wide enough for two boats to pass and had two towpaths with a span of around 8m.

The railway age had, however, begun some 30 years before and few doubted that this was the way forward with regard to the transporting of materials and possibly people. Huge amounts of money began to pour into railways and there was enormous pressure to get lines completed. Building a tunnel was a huge financial pinch-point in construction.

The first railway tunnels were built at Liverpool on the Liverpool to Manchester line, through some of the best ground conditions possible for tunnel construction - Bunter Sandstone.

George Stephenson and his son Robert soon gained skills in tunnel construction in this medium.

There were no single-track tunnels, as the lessons of narrow canals and the bottlenecks caused by narrow tunnels had been learnt.

Despite this Robert Stephenson, on his first commission away from his father, built Glenfield Tunnel on the Leicester to Swannington Line as a single-track tunnel.

Stephenson had expected sandstone, as in Liverpool, but only found running sand. Just before the opening, large sections of the tunnel sidewalls had to be rebuilt as they were in poor condition with bad bricks and very weak mortar. Robert Stephenson was, however, to go on to build almost 20% of the railways in Britain, of which the London to Birmingham is probably his most famous line with many significant tunnels.

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