Water tightness by final lining with programmed waterproofing construction joints in conventional tunneling

In conventional tunneling, as an alternative to the use of a PVC membrane installed between primary and secondary supports, water tightness could be guaranteed by adopting waterproofing construction joints in the final lining and if necessary in the invert arch. Using this technology, tightness could be more effectively ensured. The absence of the PVC sheet, involving the long-term durability of primary supports using alkali-free sprayed concrete and steel ribs with a circular section, permits to consider, for the long-term stability, both primary and final lining as a composite single resistant structure. The study illustrates how it is possible ensure effective and durable water tightness by eliminating the traditional membrane. It describes the operative facilities and quantifies, from the results of interaction numerical analyses for three different geotechnical contexts, the percentage of concrete saved.