Environmental protection is having an increasing impact on the choice of the tunnel option for major projects, from the largest high speed rail tunnel now beginning in the Netherlands (p26), to microtunnels for a flood scheme in Chichester.
In the Netherlands, the extra expense of tunnel construction is justified by the need to retain what little green space is left in the crowded Dutch landscape. In Dublin, where another big tunnel is due to begin soon (see p34), it will keep port traffic away from the city centre.
Microtunnels also score in avoiding disruption, or damaging existing parks and nature facilities, as on the featured sewer project in Stockholm (see p32).
Safety is also becoming much more important and is a factor driving up the size of tunnels. The Dutch railway bore, at 14.87m, is the largest machinedrive ever made, because frequent cross connections are vital both for pressure effects and as fire and accident escape routes.
In this issue we also look at the troubles caused by flint on the new Thames bore for the Channel Tunnel Rail Link and various new projects worldwide (p28).