ABSTRACT
This chapter explains the concepts on which most construction methods are based, establishes their field of application and estimates the advance rates obtainable with them. Selection of the most appropriate tunnel construction method, out of many available, leads to the one which provides higher safety and lower construction costs. The traditional method for underground tunnel construction is based on the repetition of elementary operations: excavation, load of the excavated grounds and execution of the tunnel support, which constitute the work cycle. Since inverts are used in sections with more unfavorable stress–strain behavior, this element of reinforcement should be combined with those already described, namely: elephant feet and forepoling placed prior to the excavation. The concept of the self-supported vault method has been developed, which is a variant of the top heading and bench method, supplemented with elephant feet and forepoling placed prior to the excavation to support the vault structure.
