ITA – AITES – Guideline “Conventional Tunnelling” published

On the occasion of the 2001 World Tunnel Congress in Milan/I the ITA initiated Working Group 19 “Conventional Tun-nelling”, which was charged with tackling the issue of conventional tunnelling. After a constitutional phase the WG embarked on the project to work out a general guideline on conventional tunnelling following the 2004 WTC in Singapore. In the course of the years that followed various national contributions were collected and ultimately compiled to form a document that received mutual approval. On the occasion of this year’s WTC in Budapest the guideline was published on the new-look ITA Homepage (www.ita-altes.org).
The aim of the newly published guideline is to promote better understanding among clients, contractors and tunnelling engineers at international level. This is brought about on the one hand through a standardisation of terms and on the other through a presentation of the current state of the art.
The guideline is intentionally couched in general terms and rejects the direct acceptance of national terminology to facilitate as much application at international level as possible. As a result only fundamental principles are examined without going into specific details, which are often the subject of national standards or contained in specialised literature.
During the working out of the guideline it was first of all imperative to clarify the term “conventional tunnelling”. Conventional tunnelling denotes the production of underground structures with any desired cross-sectional form in a cyclic process of execution through
– excavation using a drill+blast drive or a mechanically-supported drive with any desired equipment except for full-face tunnelling machines
– mucking
– installation of primary rock supports with facilities such as
– steel arches or lattice girders
– ground or rock anchors
– shotcrete or in situ concrete, both in reinforced or unreinforced state using netting or steel fibres.
In addition the report displays the high flexibility of conventional tunnelling in pronouncedly changing subsoil conditions, particularly given the application of the wide-ranging catalogue of ancillary construction measures.
However, it was clearly pointed out that such high flexibility can only then be exploited providing that the contractual conditions allow for speedy and competent decisions. This can only be achieved if the construction site organisation is made up of experienced tunnellers both from the side of the contractor as well as the client and the organisational set-up permits prompt decisions. Furthermore the WG concludes that conventional tunnelling must be based on standard price contracts.
The guideline touches on the following aspects of conventional tunnelling:
– planning
– construction methods
– measurement technical mo-nitoring during execution
– aspects relating to the works contract
– construction site organisation.
The specifications provided basically relate to all underground structures such as transport tunnels, chambers, hydraulic tunnels, utility tunnels and shafts. Issues relating to constructing chambers and shafts are not dealt with at length however.
The guideline regards itself as an aid for better international understanding and by no means as a “cookery book” on conventional tunnelling for inexperienced readers. Conven-tional tunnelling leads to success providing that the decision-makers on the spot possess the necessary technical knowledge coupled with the corresponding experience.
Heinz Ehrbar, Chairman ITA WG 19