ITA GUIDE | TRENCHLESS


Table 2: Indicative drive lengths (e.g. between shafts) and maximum number of drives Excavation technique


<1.2m 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


distance limited by equipment capability


Non Man Entry:


1.2m <250m


250m to 500m (see Notes)


125m


1.5m <500m


to 750m (see Notes)


300m *250m *50m


1.8m <750m


>750m (see Notes)


750m *500m


(plan to use mini-digger if over 2.1m dia)


*25m - Minimum cross section inside frames to be subject to rigorous risk assessment with consideration for rescue (absolute minimum of 1.2m high x 1.0m wide to be provided)


Table 3: DAUB recommendations for min. tunnel diameters (own translation) [1] TBM type:


Slurry Shield


Drive Type of logistic unit: Logistic System:


≤ 1,400 m


> 1,400 m ≤ 4,000 m


Tunnel length


> 4,000 m ≤ 6,000 m


> 6,000 m ≤ 10,000 m


Electric/Diesel Rail Track MSV Rail Track Minimum diameter according to EN 16191>750m (see Notes) 3.5m/3.8m 3.7m/4.0m 3.9m/4.2m


complementary publications from ITAtech and ITA-AITES, such as issued from the latter’s Working Groups – WG 5 (Health & Safety), WG14 (Mechanised Tunnelling) and WG23 (Shafts). It also refers to information issued in the last few years from the PJA.


PJA GUIDANCE Just over two years ago the PJA updated its guidance documents by issuing ‘Pipejacking design guidance for CDM Duty Holders’, which replaced ‘Tunnelling & Pipejacking Guidance for Designers’. The original guidance had been a key source


document to the trenchless tunnelling industry predominantly in the UK but was also used as a reference document used internationally. The updated version reflected changes to UK regulation and in equipment capabilities. The update is a best practice consensus agreed


between the PJA and the British Tunnelling Society (BTS). It must be read in conjunction with BS6164 ‘Health & Safety in Tunnelling in the Construction Industry’ – and, crucially, is only for use by those “competent to plan, design and construct pipejacks and microtunnels,” the PJA said. It is based on experience of the occupational


health and safety risks arising from heavy physical and handling activities, including: use of vibrating tools; working in confined spaces; evacuation or rescue in “a range of reasonably foreseeable situations.” Risks to be managed can include: atmosphere;


3.8m/4.1m 4.0m/4.3m 4.2m/4.5m 3.6m/3.9m 3.8m/4.1m 4.0m/4.3m 4.0m/4.3m 4.2m/4.5m 4.4m/4.7m


heat & fire; ground conditions; ground gases, water & contamination; and ventilation. The guide may require a tunnel ID to be larger to also satisfy hydraulic or other use needs. Legal responsibilities, though, remain with the CDM Duty Holder. The guidance can be varied, by judgment, in


light of technology improvements, better working practices, or risk mitigation measures. The two tables from PJA concern internal


dimensions and indicative drive lengths, respectively. Colour-coding of risk is given for five bands of diameter: less than 1.2m; 1.2m; 1.5m; 1.8m; and, more than 1.8m. Only two methods of excavation by pipejack – by


machine and remote operation from the surface – are classed as lowest risk for all the diameters in Table 1. Even so, the guidance requires designers and contractors to assess risks in all cases, in addition to site-specific risks and specifying mitigation measures. In its Notes, the guidance says doing longer than indicative drive lengths, as given in Table 2, needs to be checked and approved by the principal designer; however, looking to exceed the indicative drive length by more than 75% is unacceptable. All hand digging is categorised as either ‘not acceptable’ or medium risk, depending on diameter.


For a copy of the ITAtech guide go to: https://about.ita-aites.org For a downloadable free version of the PJA guide go to: www.pipejacking.org


October 2026 | 29 MSV *100m


>1.8m <750m


1000m + (see Notes)


>750m (see Notes)


>500m (see Notes)


EPB


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