Tunnelling Under Rivers and Harbours

The length of the railway tunnel under the Mersey between Liverpool and Birkenhead, is 1 m. between the pumping shafts on each side of the river. From each a drainage heading was driven through the sandstone with a rising gradient towards the centre of the river. This heading was partly bored out by a Beaumont machine to a diameter of 7 ft. 4 in. and at a rate attain ing occasionally 195 ft. per week. All of the tunnel excavation, amounting to 320,00o cu.yd., was done by hand labour, as heavy blasting would have shaken the rock. The minimum cover is 3o ft. between the top of the arch and the bed of the river. Pump ing machinery is provided for 27,000,00o gal. per day, which is more than double the usual quan tity of water. Messrs. Brunlees and Fox were the engineers and Messrs. Waddell the contractors for the work which, taking six years, was completed in 1886.

Some 3o m. of brick-lined waterworks tunnels have been built under the Great Lakes since 1864, mostly in clay, without the use of shields, although in the later ones compressed air was utilized. A large portion of one of the tunnels at Cleveland, 0., 9 ft. interior diameter, was built at the rate of 17 ft. per day at a cost of about $18 per foot. During this work three explosions of inflammable gases occurred in which 19 men were killed and others were injured. Later a fire at the shaft in the lake caused the death of ten men. Work was thereafter completed under the direction of George H. Benzen berg. Less serious accidents, principally explosions of marsh gas, occurred in many of the other tunnels.

In 1869 P. W. Barlow and J. G. Greathead built the Tower footway under the Thames, using .for the first time a cast iron lining and a shield which embodied features of Brunel's design.

First Tunnel in Compressed Air.

Compressed air was first used in tunnel work by Hersent, at Antwerp in 1879, in a small drift with cast iron lining. In the same year compressed air was used for the first time in any important tunnel by D. C. Haskin, in the famous first Hudson River tunnel, from Hoboken, N.J., to Morton street, New York city. This tunnel was to be of two tubes, each 16 ft. wide by 18 ft. high. In June 188o the north erly tube had reached 36o ft. from the Hoboken shaft. The compressed air blew a hole through the soft silt of the roof at this spot, and the water entering drowned the 20 men. With British capital and largely under the direction of British engi neers (Sir Benjamin Baker and E. W. Moir), the northerly tun

nel was extended 2,000 ft. to about three-fourths of the way across but in 1891, the tunnel was allowed to fill with water and it so remained for ten years. Both tubes were completed in 1908, under the direction of Charles M. Jacobs, engineer. In the meantime, two others were started crossing under the Hud son from beneath the Pennsylvania railroad station in Jersey City to Cortlandt street, New York, and connecting tubes on the New Jersey side paralleling the Hudson river. These tunnels which form parts of the Hudson and Manhattan railroad system, were put in operation in 1910 under electric traction by third rail. (See ELECTRIC TRACTION.) The use of compressed air in the first Hudson tunnel, and of annular shields and cast iron lining in constructing the City and South London railway (1886-9o) by Greathead, became widely known and greatly influenced subaqueous and soft-ground tun nelling thereafter. The pair of tunnels for this railway, from near the monument to Stockwell, from io ft. 2 in. to io ft. 6 in. interior diameter, were constructed mostly in clay and without the use of compressed air, except for a comparatively short dis tance through water-bearing gravel. In this gravel a timber heading was made, through which the shield was pushed. The reported total cost was £840,000. Other tunnels, lined with cast iron segments and constructed by means of annular shields and the use of compressed air, were constructed after the City and South London work was well advanced.

The St. Clair River tunnel (Joseph Hobson, engineer) from Sarnia to Port Huron, Mich., was built in 1889-90, through clay, and for a short distance through water-bearing gravel. It is 1.14 m. in length and 21 ft. external diameter. This tunnel was the first one completed in America in which were used all the essential elements for successful subaqueous work; i.e., a shield, compressed air and cast-iron rings.

In 189o-93 a shield-driven vehicular tunnel was constructed in sand and gravel across the Clyde in Glasgow, Scotland. It consists of three parallel cast iron tubes with an internal diameter of 16 ft., the centre one being a footway and the outer tubes for vehicles in each direction. The footway is reached by inclined ramps and stairs, but the vehicles are lowered and raised by elevators in shafts of 76 ft. inside and 8o ft. outside diameter.