UNDERGROUND RAILWAYS AND TUNNELLING, AN OVERVIEW OF BRITISH ACTIVITIES

Although tunnelling has been slow to enter the scientific age, and variable and difficult ground conditions have hampered attempts to devise efficient mechanical excavation and support systems, several significant improvements have been made in recent years. These advances have occurred in the areas of geotechnical investigation, excavation, groundwater management, and tunnel lining. Largely as a result of these improvements, thorough site investigations and the consequent development of a tunnelling system are now carried out prior to driving a tunnel. Modern tunnelling, as opposed to cut and cover construction, offers advantages of minimal surface disruption and comparable or reduced costs. Although it requires a high capital cost, the underground location of rapid-transit systems provides an efficient and convenient mode of transportation that is more energy-efficient than other forms of wheeled transportation. Urban redevelopment also can be centered around an underground transportation system by the construction of public and commercial facilities along the route.(a)