TECHNICAL | CONVENTIONAL TUNNELLING
CONVENTIONAL TUNNELLING IN URBAN SETTINGS
ITA Working Group 19 recently published guidelines for the design and construction of conventional tunnelling works in urban settings.
In its recently published 71-page report, the International Tunnelling and Underground Space Association’s (ITA) Working Group 19 (WG19) thoroughly packed-in information and illustrations when putting the focus of its brief – Conventional Tunnelling – onto particular challenges and applications on projects in cities. Published in April, as ITA Report No39, the document
is called ‘Guidelines for the Design and Construction of Conventional Tunnelling in Urban Settings’. Well-illustrated with abundant photos, drawings, graphics and tables, the guideline addresses its theme over a dozen chapters, the last of which is a 24-page block packed with summarised case studies – 14 in all – from across the world.
Above:
ITA report on conventional tunnelling in urban settings. Image credit: ITA
REPORT STRUCTURE Before the list of case studies and briefings on their geology, challenges and solutions, the ITA report invests 43 pages, structured in 11 chapters, to extensively – but succinctly – discuss design and construction for conventional tunnelling. A few pages, comprising the first chapter, introduce the report and its purpose, which arises, it says, from conventional tunnelling having become “a preferred method” of underground construction for many major tunnel projects in cities. It defines conventional tunnelling as “a cyclic
excavation followed by the sequential installation of temporary support”, such as the New Austrian Tunnelling Method (NATM), Sequential Excavation Method (SEM), Sprayed Concrete Lining (SCL), and so on. The report notes the flexibility and adaptability of conventional tunnelling below ground and, up on the surface, how it helps to avoid impacts of opening up urban environments such as required using the Cut and Cover (C&C) method. The focus on the advantages of conventional tunnelling and its increased use comes as urban environments expand, as does the associated infrastructure. The complexity of construction projects and associated challenges – especially with varied geology, often low cover to tunnels, and a host of known as well as unchartered utilities and foundations – leads to more need to discuss conventional tunnelling. Following the Introduction, ten chapters look at:
● Geotechnical and hydrogeological investigations ● Design process ● Assessing ground behaviour during excavation
20 | August 2026
● Instrumentation and Monitoring (I&M) ● Ground improvement ● Pre-support ● Impact risk to infrastructure ● Excavation support classes and field collaboration ● Risk management and robustness of design ● Contractual requirements – recommendations.
SPOTLIGHT: RISK AND CONTRACTS Across Chapters 10 and 11, the report looks at matters of assessing risk, ensuring robustness in design, and also offers recommendations for contractual requirements. Chapter 10 refers back to the Introduction, recalling
the advantages offered by conventional tunnelling but also the many complexities and challenges that arise in urban settings due to both natural and artificial structural features, and others, known and unchartered. The report takes the view, consequently, that choosing conventional tunnelling “carries a higher level of risk” than that of other tunnelling methods in cities, or use of the sequential approach in other, non-urban settings. “Conventional tunnelling, especially in urban areas,
imposes risks on the owner, the contractor, the designer and the public,” says the report. Approaches to risk management and mitigation
are therefore discussed, including who should initiate and the need for a “living” Risk Register. Turning to construction contracts, the ITA report addresses the subject by discussing points to the following structure: pre-qualification of contractors; the need for experienced engineers and personnel in design, construction and management; risk sharing; contract and project delivery models; responsibilities during tunnelling; payment; and time-dependent costs. Again, there are references for further reading. Concluding the chapter, the recommendations
reiterate the need for comprehensive and effective risk management but also add that there should be a Geotechnical Baseline Report (GBR); use of Early Contractor Involvement (ECI) – which can be adopted under a wide range of delivery methods, it is noted; daily site meetings; unit costs; compensation for unforeseen/differing site conditions; and, it is “highly recommended”, use of the FIDIC Emerald Book or its risk-sharing elements.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45
