ITA GUIDES | MECHANISED TUNNELLING
ITA GUIDES ON EQUIPMENT, THRUST & LINING
Guides on TBM equipment specification, thrust force for shield driving in weak rock, and segmental lining condition during operational life, respectively, were recently published by ITA-AITES
Three recent tunnelling guides published for the industry cover a range of aspects of mechanised equipment and systems for bored tunnels. The guides were issued from the Working Groups of the International Tunnelling and Underground Space Association (Association Internationale des Tunnels et de L’Space Souterrain - ITA-AITES). The three reports focus on the following themes: recommendations for tunnel boring machine (TBM) equipment specification; assessing thrust force for open mode drives in weak rock; and, post-construction, the ways to inspect and judge the condition of segmental lining during operational life of bored tunnel assets. As the joint output of two Working Groups (WG)
- WG 3 & WG14 - the ‘Recommended Guidelines for Tunnels Boring Machine Equipment Specifications’ is ITA Report No. 43, and was published in February. Broadly, the report considers advancing technology
in the light of different procurement methods and aims to support conversations, and more rounded decision-making, among project owners and the supply chain parties. It feeds in, therefore, to the discussions of risk management and procurement, such as from possibilities for technological and performance opportunity versus data availability in wariness and perhaps limiting specifications being set early in the project.
...AVOID ALL MATTERS THAT ARE BEST LEFT TO A KNOWLEDGEABLE AND CAPABLE TUNNEL CONTRACTOR.
In that balance, it says “The goal is therefore to
limit the prescriptive details to only fundamental elements and avoid all matters that are best left to a knowledgeable and capable tunnel contractor,” which can limit risks while being open to innovation and alternatives. The 50-page guide covers its aims in six chapters
- dominated by far by the final chapter, at more than 40-pages in length. Yet, in pursuing such complex discussion it is - perhaps thankfully for some, and certainly adding to its easy reference utility - it is light on the volume of heavy narrative text.
Instead, it takes the approach of devoting itself
more to providing structured information, conveyed in highly accessible tables. Given the variety of audiences, and backgrounds, that such discussions of risk and procurement will necessarily involve, this is an excellent communication tool to potentially educate and inform so many. The report is discussed further below. In the second of the recent ITA reports under
consideration here, the focus is on assessing the thrust force for open mode shielded TBMs driving in weak rock. It is a comparatively shorter report, at 21-pages, which is reasonable given that its technical subject matter is more niche. The guide has six sections with most of the discussion in one chapter, considering different aspects of friction forces on a shield. It is well illustrated and referenced. Why such a guide
for an area of such a niche focus? Well, get the calculation wrong and the shield will go nowhere, and of course the segmental lining design (for the TBM pushes off the built rings) will likely not be optimal. As the guide points
out: “The assessment of the TBM thrust force required for excavation is of paramount importance for the design of a Tunnel Boring Machine, and of the tunnel lining when the thrust force is applied against precast segments.”
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Below: ITA guide on TBM equipment specifications.
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