Environmental and geotechnical considerations for the use of bored tunnels in urban areas

Many advantages are to be gained from the use of bored tunnels, as opposed to shallow excavations, for the development of infrastructure in urban areas. This option is however rarely adopted in developing countries due to a lack of knowledge of the specialist skills and geotechnical processes required to ensure timely and econcmical construction. This paper discusses the environmental advantages favouring the use of tunnels, particularly for major contruction projects. The need to establish geotechnical conditions accurately prior to excavation is illustrated in conjunction with appropriate site investigation techniques. The range of modern tunnelling methods is presented. Emphasis is given to the use of fully mechanised techniques for the excavation of tunnels in both rock and soils. Finally, the requirement to minimise the costs for tunnelling work is considered, and specific recommendations are made to illustrate how this can be achieved.