New Thames Tunnel
The London County Council Preparing to Run Another Tunnel Under the River Connecting Greenwich with the Isle of Dogs
Hardly was Blackwall Tunnel out of hand when the London County Council turned its attention to another sub-aqueous scheme. This time the claims of Greenwich and the Isle of Dogs were considered. There is a lot of passenger traffic between the two places, but it is left to the Great Eastern Company's steamers. The hundreds of workmen and workgirls who have to cross morning and night are therefore compelled to pay daily fares. Even workmen's wives on the Millwall side are forced to use the steamers to go marketing in Greenwich.
For Foot Passengers Only
At first the Council thought to make a tunnel slightly smaller than the one at Blackwall to carry vehicles as well as passengers, but this project was soon dropped. The Millwall Docks on the Isle of Dogs made it impossible to construct the necessary approaches. Besides, there was little promise of any vehicular traffic, with Blackwall Tunnel so near on the one side, and the promised Rotherhithe tunnel between the island and the Tower-bridge on the other. Communication between the two banks was needed wholly in the interests of the working people of both districts, so it was decided to make a footway tunnel only. Out of four tenders that of Messrs. Cochrane was accepted a few days ago for £109,500. The approach to the tunnel on the Greenwich side will be from the north end of Church-street, in the rear of the famous Ship Tavern. On the Millwall side the approach will be by a footpath 15ft. wide at the western end of Island Gardens. The depth of the tunnel at the centre of the river will be about 72ft. below the ground line.
Compressed Air to be Used
From shore to shore the tunnel will be exactly 1,217ft. in length. It will be accessible by a shaft on both sides of the river, sunk to an average depth of 50ft. Each shaft will be formed by sinking a steel caisson with a special cutting edge, the inside diameter of which will be 35ft., and the outside diameter 43ft. The weight of the steel in each of the shafts will be about 250 tons, and the space between the two skins will be filled with concrete. The shafts will be sunk by means of compressed air, a special air-tight floor being provided in each shaft a few feet above the bottom for this purpose. The air-tight floor will be provided with air-locks for the removal of the excavation and the ingress and egress of the men working. There will be an opening 15ft. in diameter in each shaft for tunnel entrance, and during the sinking of the shafts these openings will be plugged by steel plugs, which will be removed when the tunnelling operations are commenced. The work will be begun at the Poplar end of the tunnel and the excavation will be removed by means of a shield about 13ft. 3in. in diameter, compressed air being used for excluding the water.
Municipal Journal and London, February 24, 1899