As part of the realization of the contract T225 for the construction of the new metro line in Singapore, Bessac completed a pipe-roof using a slurry micro tunneling machine in order to protect an existing metro tunnel during the construction of the new one.
The pipe roof consists of up to 6 drives, 53m long each in order to from a vault. A total of 318m is excavated using micro tunneling. This vault has a minimal cover of only 1.35m with the existing metro line remained in service during the works.
Bessac designed and manufactured a solution to modify an existing micro tunneling machine in a retractable micro tunneling machine. The MTBM used is a slurry micro tunneling, type AVN 800 XC which is installed in an extension kit allowing to enlarge the external diameter of the shield to be retractable. The lining is made of 1270mm steel pipes, with a unit length of 4m. Pipes are welded together using an automatic orbital welding system to ensure the longitudinal liaison.