Introduction

The frontispiece shows a photograph from the world’s first bored tunnel. It is also a good example of the influence of jointing on overbreak. The exploratory Beaumont Tunnel was driven in chalk marl in 1881-1882. The classic wedge-shaped fall-out caused by three joint sets intersecting the tunnel wall was also a source of major difficulties when the Channel Tunnel was driven by much larger machines some 110 years later. The Beaumont TBM of 2.1 m diameter achieved weekly advance rates of between 30 and 60 m ( Varley & Warren 1996 ), a highly respectable effort but later overshadowed by much higher performances and a best week of 426 m, by the time the 8.7 m diameter twin-tube Channel tunnels were completed in 1990-1991 ( Warren et al. 1996 ).