TECHNICAL | MECHANISED TUNNELLING
cutterhead and screw conveyors, respectively; thrust
force; and more. Assessment is further informed by constant review
of the conditioned soil, at exit from the screw and also along the conveyor belt. Continuous adjustments of the four foam parameters are possible, and typically made in either automatic or semi-automatic ways. The guide says that while more manual modes
are sometimes possible they are “generally not recommended and rarely used for TBM excavation.”
SEALING PRODUCTS Main Bearing The guide notes that TBM bearing lubrication is a “quite complicated” topic, from the perspective of outsiders and that literature is limited on different systems and considerations for ground conditions. That said, it further notes there are two commonly
available types of main bearing seals: multi-lip polyurethane (PU) seals; and, nitrile butadiene rubber (NBR) seals. Their characteristics lead to different overall design and also sealing system needs, and consequently
supporting products. The guide focuses on sealing system for products common to pressurised machines and notes that, while not required, they can be used in non-pressurised machine applications.
Tailskin Important to the success of the full TBM tunnelling system, especially in soft ground, is the important role played by tail sealants and also the type used to seal the gap between segments, says the guide. The tail sealant is to stop ingress of water or entrance
of soil, gas or backfill grout into the TBM working area. A stiffer, first-fill special formulation of tail sealant for the first filling of tail brushes before launch of the TBM. Proper filling is key. Then, during tunnelling the tail sealant ‘pastes’ are
continuously injected through the tail shield into the shield brush chambers. The guide discusses the tail sealants over four-pages,
in sections covering: Description; Definition; Quality Control & Laboratory Testing; Site Testing; Consumption Estimation; and, Performance Factors.
GUIDE: TBM SERVICES The guide on TBM Services is compact – with 11-pages of content
after covers and contents pages are allowed for. But they are a valuable and offer guidance that continues to be important and noteworthy, even though the ITA document (Report No12) – ‘ITAtech Guidelines on Services of Machinery for Mechanized Tunnel Excavation’ – came out in 2021. The report says: “The correct understanding of TBM Services at
the start of the project will help project owners, designers and TBM users realise correct planning of the works.” Given such critical importance for knowing about and setting
up for TBM Services, one of the aims of the guide is to create a “common language in terms of TBM Services” and approaches it goal of doing so by listing all potential activities for scheduling as well as their ideal sequencing. It adds that TBM Services feeds into the correct planning of the
works, which “will minimise both technical and commercials risks for the project.” After the Introduction, the guide has three principal chapters – Definition of TBM Services; Service Activities; and, Service Provision and Contracts. Each is short, in the overall compact document, with the largest being Service Activities, itself having seven sections. While noting that all activities in preparing for and using TBMs is a long and multi-step process for projects, and in some cases it may be considered that TBM refurbishment should be classed as Service activity, this is not the case for this report. The guide does not cover this TBM refurbishment and notes that, instead, the activity is considered in separate guidance, published earlier (2019), as ITAtech Report 5-v2 – ‘ITAtech Guidelines on Rebuilds of Machinery for Mechanized Tunnel Excavation’ – which also came from the ITAtech activity group Excavation.
Looking at each of the principal chapters:
Definition of TBM Services Over less than two pages, the Definitions chapters has eight sections, as follows: Transport; Planning of the Works; Jobsite Assembly, Reassembly, Disassembly/Transfer Works; Maintenance; Qualification of Personnel; Supply of Spare and Wear Parts; Supply of Excavation Tools; and, Lifting Works. Most discussion is on the Jobsite and Personnel sections. On Jobsite, three typical scenarios for participation of the TBM manufacturer or other service provider, although it is noted that combinations may be used: Assistance Model; Lump Sum Model; and, Turnkey Model. On Personnel, there is delineation of what constitutes different classes and levels of qualified workers for TBM Services.
Service Activities Many of the sections listed in the previous chapter are further examined in this, the longest, chapter of the report and does so over seven sections within six pages. Like much of the rest of the report, the pages are primarily text, illustrations being few. The largest of the sections are the three covering Transport, Maintenance and Excavation Tools, respectively. The latter section is the longest of them and covers requirements of suppliers of excavation tools, ensuring their onsite availability, stock keeping, data management on consumption, and both onsite and offsite reconditioning of tools.
Service Provision and Contracts In three sections, the chapter looks at business models for Personnel, and contracts for Spare Parts and Excavation Tools, respectively.
30 | July 2024
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