MECHANISED TUNNELLING | TECHNICAL
ITATECH GUIDES ON CHEMICALS, SERVICE
ITAtech has many industry guides for a range of tunnelling activities, and earlier this year added to its offering on mechanised tunnelling a guide on chemical consumables. The publication joins another also focused on TBMs, from a few years ago, on specifying requirements for TBM services
Many strategies and activities need covered
to prepare for executing excavations by mechanised tunnelling and these have been discussed in guidance from ITAtech in the last few years, among other publications from
the International Tunnelling and Underground Space Association (ITA-AITES). Most recent among the
reports from ITAtech’s activity group Excavation is the guide on Chemical Consumables. It was published earlier this year and follows a number of prior reports from the activity group that include looking at how best to specify requirements for TBM
Services, and also TBM refurbishment. The latest report, on Chemical Consumables, focuses
on two areas, respectively: foam for soil conditioning; and, sealing products for the Main Bearing and Tailskin. The TBM Services report, published in 2021, is a
valuable focused briefing – even if in a document of only 16-pages. It presents top-line information needed by project owners, designers, TBM users, manufacturers and service providers when specifying requirements for ‘TBM Services’ (see box).
GUIDE: CHEMICAL CONSUMABLES In February, ITA-AITES published the latest report from the ITAtech activity group Excavation, focused on the narrow area of chemical consumables but being vital it has produced a 20-page guide on the subject. The guide is ITA’s (Report No34) – ‘Chemical
Consumables for TBM Excavation’ – came out in February 2024. After allowing for covers and introductory matter, the bulk of the guide, delivering the value, is 16-pages of important and well-illustrated information. The subject is so focused that a Contents page is dispensed with – leaving eight chapters to discuss the aspect of chemical consumables for TBM tunnel boring.
As the guide observes, TBMs are complex machines
made up of several systems which use a variety of specialised products to support or enhance their operations. The guide begins with an Introduction that focuses
on use of foam for soil conditioning. From there, subsequent chapters discuss: Use of Polymers and Additives; Basic Laboratory Tests; Environmental; and, Installation and Recommendations. Further chapters discuss Sealing Products – for the
Main Bearing and Tailskin, respectively. These areas of the TBM are given six-pages in the guide, and the bulk of those are focused on the Tailskin chapter (four- pages). References are also provided, focused on
biodegradation, chemical testing, and spoil handling.
FOAM FOR SOIL CONDITIONING The guide says that foaming agents, with water, “are the most important and common materials used for soil conditioning” when tunnelling with TBMs – and different products can help to increase viscosity in granular soils or decrease stickiness in cohesive soils. The main ingredient in the foam agent, it adds, is
a single surfactant or a combination, and they allow bubbles to be formed once air is added to the agent- water mix. Then, some other ingredients help adjust their technical performance characteristics, such as foam durability, muck lubrication, and muck dispersing action. Other performance characteristics also consider
the size of the TBM, environmental impact, geological variation along a tunnel route, and, of course, commercial aspects. In support of all of those considerations,
performance control of the foaming agents for soil conditioning uses the following technical parameters: Foam Concentration (Cf); Foam Expansion Ratio (FER); Foam Injection Ratio (FIR); and, Water Injection Ratio (WIR). The foam parameters are predefined by using
dedicated lab tests. Then, during tunnelling, the soil conditioning parameters are established by TBM engineers. Control rests with TBM operators as they consider performance, such as torque of the
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