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Blackwall Road Tunnel, northbound
Greenwich to Poplar, London, UK
associated engineer
Sir Alexander Binnie
Ernest William Moir
date  1892 - 1897, opened 22nd May 1897
UK era  Victorian  |  category  Tunnel  |  reference  TQ387801
ICE reference number  HEW 2202/01
The first of the Blackwall Tunnels was the third tunnel to be constructed under the River Thames in London. Its dimensions allowed for two-way horse-drawn traffic, and it includes two sharpish bends. Today, after refurbishment, it remains in constant use and carries northbound traffic on the A102 between Greenwich and Poplar in Docklands.
During the 18th and 19th centuries, East Londonís manufacturing districts spread east along the river and the need for permanent links ó rather than ferries ó between north and south banks increased.
The 1843 Thames Tunnel from Wapping to Rotherhithe, designed by Sir Mark Isambard Brunel (1769-1849), was the first under-river tunnel to be completed. The second tunnel was the 1870 Tower Subway, crossing under the river on the west side of the Tower of London, and designed by Peter William Barlow (1809-85) and James Henry Greathead (1844-96).
By 1875, it was clear that the construction of more crossings was imperative. But any new road tunnel would need to be toll-free to compete with the existing bridges for custom (the two earlier tunnels were tolled). The first attempt to construct a tunnel between Blackwall and the Greenwich peninsula was made by the Metropolitan Board of Works, who proposed several schemes and obtained the Thames Tunnel (Blackwall) Act in August 1887.
In the same year, Sir Joseph William Bazalgette (1819-91) prepared a design consisting of three parallel tunnels, two for vehicles and one for pedestrians. Completion was intended within seven years. However, the newly formed London County Council replaced the Metropolitan Board of Works on 21st March 1889, before the contract could be let.
By 20th November 1890, the councilís new chief engineer Alexander Richardson Binnie (1839-1917) had produced a new single tunnel design under the 1887 Act. The subaqueous portion of it passes through clay, sand and gravel subsoils, which presented problems for the tunnellers. Binnie had to use a range of construction techniques to succeed, including a tunnelling shield and compressed air.
He drew on the expertise of Greathead for the shield and Sir Benjamin Baker (1840-1907) for working in a compressed air environment. Baker had been a consultant on the troubled Hudson River Tunnel between New York and New Jersey, whose episodic construction took place in 1873-1904, and also the St Clair Tunnel from Port Huron in Michigan to Sarnia in Ontario, built 1888-91.
S. Pearson & Son Ltd, founded by Samuel Pearson in 1844, submitted the winning tender of £871,000 ó coincidentally the same contractor that worked on the Hudson River Tunnel with Baker. The Blackwall Tunnel contract was let in 1891 and work began the following year.
The tunnel runs between East India Dock Road at the north end and Tunnel Avenue to the south. It runs below ground for 1.36km and is 1.9km overall. This includes the open approaches, which slope down at 1 in 34 over the northern 267m and 1 in 36 over the southern 262m. The cutting sides are lined with glazed brickwork 229-457mm thick backed by concrete and a 38mm layer of asphalt for watertightness. Constructing the approaches necessitated diverting and reconstructing a number of sewers crossing the tunnelís path, in particular the egg-shaped 3m by 2m Isle of Dogs low-level sewer.
The entrances to the underground tunnel sections have portals of polished brown granite blockwork. The stretches beyond the portals were constructed in rectangular trenches using the cut-and-cover technique ó 132m on the Poplar side and almost 280m on the Greenwich side. The trenches, shored with heavy timbers, were 11.3m-12.8m wide and 11m-20m deep.
On the north side, and the first 102m of the south side, the circular tunnel consists of four concentric rings of brickwork 457mm thick, surrounded by 356mm of asphalt and mass concrete, with a puddled clay seal around the concrete. However, the clay could not be made stiff enough to prevent the tunnelís sides from bowing outwards when the trenches were backfilled. Further movement was stopped by driving piles through the fill into the layer of clay puddle at the sides of the trenches.
The remaining 178m of trench on the south side omitted the clay layer ó the concrete surround filled the trench. The tunnel wall has an extra course of brickwork in this section, which was dewatered during construction using three pairs of rocker pumps.
The central 950m was driven with a tunnelling shield and has a cast iron lining. Compressed air was used to increase pressure within the 8.23m diameter bore, keeping water out of the excavation. The tunnel invert level ó 24.38m below Trinity High Water ó corresponds to the maximum depth of water pressure thought advisable at the time for men to work in. So the crown of the lining was within 1.52m of the river bed in places.
Work began by sinking four shafts, in iron and steel caissons, the positions of which were determined by horizontal or vertical changes in direction. The tunnel was then driven in a straight line from shaft to shaft, avoiding the expense of a specially-shaped shield and the difficulty of driving it to a curve.
Shafts 1 (TQ384804) and 2 (TQ384803), north of the river, are in gravel soil that was excavated by a 10.2 tonne crane grab supported on girders inside the shaft. Water was removed afterwards by a combination of pumping and compressed air blowing. Shafts 3 (TQ387800) and 4 (TQ389799), to the south, were sunk by pumping out the water to enable dry excavation within.
The caissons are 14.6m diameter internally and 17.7m externally, with double skins, of 8mm-19mm thick plating. The skins braced together by horizontal and diagonal angle irons and stiffened using vertical diaphragms. The area between the skins is filled with concrete.
Each caisson was fabricated with two round tunnel openings, 9m in diameter, closed during sinking by removable iron shutters. Airtight iron floors of 16mm buckled plates, resting on 457mm deep girders, were fixed above the openings, and surmounted by 1.2m and 3.7m deep girders to resist the pressure.
Once each shaft was in position, its floor was made watertight using wrought iron plates attached to the inside of the caisson with studs, topped with a layer of concrete up to 3.4m thick. The inner surface of the shafts was then lined with glazed brickwork, giving a finished diameter of 13.9m.
Ernest William Moir (1862-1933), the contractorís agent, designed the steel tunnelling shield, which weighed 254 tonnes. Moir had been Greatheadís assistant on the City & Southwark Subway in 1886-90, and also worked on the Hudson River Tunnel. The new shield was constructed in a temporary dry dock located in the cut-and-cover trench adjacent to Shaft 4. Dock and shaft were flooded, the shield floated into the shaft and the water pumped out until the shield rested on a timber cradle.
The tunnel was driven northwards from Shaft 4 to Shaft 1. The section between shafts 3 and 2, under the river, took 54 weeks to complete. Some 800 men worked on the tunnelling, which took place between March 1892 and September 1896. The tunnel was lit by three rows of electric roof lamps.
To repel water from the excavation, compressed air at 186kN per sq m above atmospheric pressure was fed into the tunnel via steel pipes from Shaft 4, powered by six compressors totalling 1,119kW. To prevent a blow-out, a 3m thick, 46m wide layer of clay was laid on the river bed along the line of the tunnel.
The cylindrical outer shell of the tunnelling shield, 8.43m overall diameter, was 5.94m long and 63mm thick, made of four rings of 28 full-length riveted steel plates. The face of the shield was divided into shuttered compartments through which material was excavated by hand, before the shield was moved forward by hydraulic rams, and a cast iron lining ring placed in the gap exposed behind.
Excavation spoil was taken to the surface via shafts 2 and 4. Men, materials and spoil were transported in the tunnel on a travelling platform attached to the shield. The platform was 12.2m long and almost the full width of the tunnel, running on rails fixed to brackets on the tunnel lining.
The cast iron tunnel rings, each composed of 14 segments bolted together, are 762mm long and of 8.2m external diameter. Between shafts 1 and 4, the cast iron is 51mm thick. North of Shaft 1, it measures 38mm. The lining is faced with glazed tiling on concrete, giving a finished internal diameter of 7.4m.
A brick arch over the base of the tunnel tube encloses a subway for pipes and services, above which is the 5m wide roadway, with a 950mm footway on either side. The road is drained through gullies at 15m intervals on alternate sides, and the water is pumped to the surface through Shaft 2. Originally, the road surface was asphalt, and the approaches were paved with granite setts.
Shafts 1 and 4 feature domed glass and iron roofs, and spiral staircases for pedestrian access. Shaft 2 was used for tunnel maintenance and Shaft 3 was topped by a ventilation chimney some 21m high.
In 1896-7, matching gatehouses of banded brown and red sandstone with octagonal corner turrets and steeply hipped slate roofs, were constructed at the start of the tunnelís approaches. Designed by architect Thomas Blashill (1831-1905), the rectangular buildings spanned the road with arches. Living areas were located on the first floors and attics.
During the same period, the council built an electricity generating station near Shaft 2 to light the tunnel and its buildings, as there was no public electricity supply available. The plant had a subterranean water tank, buildings for boilers, engines, offices and stores, and 36.6m high chimney.
The Blackwall Tunnel was opened by the Prince of Wales in a ceremony on Saturday 22nd May 1897. Queen Victoria awarded Binnie a knighthood. The tunnel was one of London County Councilís first contracts, and the future second tunnel (Blackwall Tunnel southbound) would be one of its last engineering projects (the council was disbanded in 1965).
The projectís safety record was good for the late 19th century, with "hardly any deaths" (seven). At the time, building a ship, or something similar, may have lost up to 20 lives. The council was concerned about the effects of working in compressed air and appointed a resident medical officer, Dr E. Hugh Snell, to examine the men and investigate any consequent illness. No deaths, but three cases of permanent illness were attributed to so-called caisson sickness. This was considered low, helped by a shorter than normal working shift of eight hours, with a 45 minute break.
In 1899, the council added public toilets to the north entrance gatehouse in an adjoining building of similar style. They were demolished in 1958, during work on the approach roads in preparation for the second tunnel.
In 1912, the Blackwall Tunnel was connected to the municipal electrical supply and the generating station closed (demolished in the late 1960s).
Resident engineers: David Hay (to 1896), Maurice Fitzmaurice
Contractor: S Pearson & Son Ltd
Tunelling shield: Eastern & Anderson
Caissons: Thames Ironworks
Tunnel lining: British Hydraulic Foundry Company
Architect (gatehouses): Thomas Blashill
Gatehouse construction: Dove Brothers
Research: ECPK
"The Bends: Compressed Air in the History of Science, Diving, and Engineering" by John L. Phillips, Yale University Press, 1998
"The Blackwall Tunnel" by David Hay and Maurice Fitzmaurice, in Minutes of ICE Proceedings, Vol.130, pp.50-79, London, 1897
reference sources   CEH Lond

Blackwall Road Tunnel, northbound