Text 2. The history of tunneling

Part 2

The great civil engineers of the nineteenth century were drawn into really grand tunneling. Two new kinds of transport created a need for tunnels. Railways had to lie on almost flat ground, and so did England's huge canal system. By the early 1800s those canals had become England's primary commercial trade network. Canals and railways, like the Roman aqueducts before them, spawned heroic tunneling through obstacles. Tunneling under rivers was considered impossible until the protective shield was de­veloped in England by Marc Brunei, a French emigre engineer. The first use of the shield, by Brunei and his son Isambard, was in 1825 on the Wapping-Rotherhithe Tunnel through clay under the Thames River. The tunnel was of horseshoe section 22'/4 by 37'/2 feet and brick-lined. After several floodings from hitting sand pockets and a seven-year shutdown for refinancing and building a second shield, the Brunels succeeded in completing the world's first true subaqueous tunnel in 1841, essentially nine years' work for a 1,200-foot-long tunnel. During the 19th and 20th centuries, the development of railroad and motor vehicle transportation led to bigger, better, and longer tunnels. With the latest tunnel construction technology, engineers can bore through mountains, under rivers, and beneath bustling cities. Before carving a tunnel, engineers investigate ground conditions by analyzing soil and rock samples and drilling test holes. Today, engineers know that there are three basic steps to building a stable tunnel. The first step is excavation: engineers dig through the earth with a reliable tool or technique. The second step is support: engineers must support any unstable ground around them while they dig. The final step is lining: engineers add the final touches, like the roadway and lights, when the tunnel is structurally sound. Worldwide efforts are under way to accelerate improvements in the technology of underground construction and are likely to be stimulated as a result of the 1970 OECD International Conference recommending improvement as government policy. The endeavour involves specialists such as geologists, soil- and rock-mechanics engineers, public-works designers, mining engineers, contractors, equipment and materials manufacturers, planners, and also lawyers, who aid in the search for more equitable contractual methods to share the risks of unknown geology and resulting extra costs.