TRENCHLESS | ITA GUIDE
SMALL DIAMETER TUNNELLING GUIDANCE
A guide on small diameter tunnelling with pipejacking and erecting segmental lining has been published by ITAtech.
Small diameter tunnelling up to 3.8m-diameter is discussed in guidance recently issued by ITAtech and focuses on the two most common construction methods used for building such lined tunnel structures – pipejacking and segmental lining. The guide (ITA Report No 49, April 2026) does not address other trenchless methods of excavation, such as auger boring, horizontal directional drilling (HDD) and box jacking. As the guidance notes, “Small
diameters impose particular challenges due to restricted internal space,”, which consequently presents constraints in many aspects of the tunnelling work such as access, working
conditions, constructability, maintenance
Above: ITA guide on small diameter tunnelling. Image courtesy of ITA.
interventions and emergency response. All together, these point to “the importance of
system reliability and safety-focused design.” To help support a focus on such awareness and thinking, the relatively brief but well-structured and compact, guide – which is 26-pages long – offers briefings under seven chapters. There is a useful Preface to set the context for the guide but no contents page to map out what is to be covered; a short reference list is provided at the end. The chapters are:
1. Preface (and so is very short) 2. Introduction – looks at terms, definitions,
<1.2m 1.2m purpose, size, build method, lining, equipment.
3. Health, Safety and Ergonomic Aspects in Tunnelling – with discussion on different methodologies, ground conditions, confined spaces. designing for safety, emergency planning
4. Applicability of Standards – a short (one-page) chapter, considering the theme in principle and then listing key standards and documents, but with a UK and European focus only.
5. Segmental Lining – outlines the process but addresses practical limitations and requirements, especially on safety operationally, including logistics and ventilation, plus emergency planning and evacuation. Guidelines from the German Tunnelling Association (DAUB) are discussed.
6. Pipejacking – covers excavation, lubrication, intermediate jacking stations, limitations for manned and un-manned methods, both of which are discussed with reference to the UK guidelines from the Pipe Jacking Association (PJA), and the notes the German information on micro-TBMs.
7. Conclusion – includes a framework for selecting the tunnelling technique.
The guide is well illustrated with images and
many tables. It says normative references cited are primarily drawn from European practice, especially the UK and Germany. Users of the guide outside Europe are advised to consult their own national standards and regulations, plus their national tunnel societies. Usefully, the guide cross-references the discussion of mechanised tunnelling in small diameters with
Table 1: Nominal internal diameter of pipeline or microtunnel lining and suitability of different excavation techniques Excavation technique
1.5m Pipejack - machine (remote operation from surface) Pipejack - machine (operator controlled below ground) Pipejack - hand dig Pipejack - machine operator controlled (+ mechanical erector) Pipejack - hand dig (+ mechanical erector) Timber heading - hand dig Low risk Medium risk Medium risk Medium risk Medium risk Medium risk Low risk 1.8m >1.8m
28 | October 2026
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