An Education in Tunneling

This article discusses the differences between the new Austrian tunneling method and the North American tunneling method, each of which was developed in response to special local conditions. The new Austrian tunneling method was originally developed in the 1950s for construction of road and water tunnels in the alps. It was generally applied to sites with extremely variable geology, requiring flexible construction methods changing frequently to meet changing and often very difficult ground conditions. Its characteristics include: (1) drill-and-blast excavation; (2) extensive use of shotcrete for early support of unstable rock; (3) extensive instrumentation to measure ground deformation; (4) a construction support system of shotcrete and rock bolts; (5) frequent use of waterproof membranes with an interior cast-in-place lining; (6) many construction decisions made jointly by the owner and contractor as work progresses. U.s. Market conditions favoured investment in high production machinery to reduce field labour costs and requirements; the u.s. Social and legal climate discouraged innovative techniques and encouraged the evolution of established methods. The North American tunneling method is characterised by: (1) extensive use of tunnel boring excavation to increase productivity and reduce labour costs; (2) greater reliance on rock bolts than on shotcrete for construction support; (3) relatively less instrumentation, because of less variable and more predictable geology; and (4) designs adapted to simple, repetitive construction for rapid progress. (TRRL)