TBM technology and the future of mining

22 October 2020 (Last Updated October 22nd, 2020 16:31)

Whether you are using an earth pressure balance (EPB) or slurry tunnel boring machine (TBM) or working with hard rock conditions, additives are an inherent part of TBM tunnelling. From soil conditioners to tail sealants, main bearing greases and annulus grout technolgies, there are many fit-for-purpose chemical solutions to make TBM excavation safe and efficient.

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TBM technology and the future of mining

With over 100 TBM project references worldwide and consequently gaining extensive experience at TBM sites and laboratories globally, Normet has developed a comprehensive range of TBM additives for any tunnel excavation project, along with the expertise to suggest the most suitable solutions and provide teams with the relevant training. In line with the company’s focus on sustainability, Normet has worked to minimise TBM chemical’s environmental impact, including minimising toxicity, high biodegradation or inert chemical behaviour, the use of renewable raw materials where possible, and excellent efficiency to minimise material consumption.

An important role of chemicals for EPB TBM job sites is soil conditioning. Foams, polymers and other additives can be injected into the tunnel face in order to modify the characteristics of soft ground. By modifying these conditions, the soil becomes simpler to transport through the mucking system and is capable of providing the required counter pressure to prevent uncontrolled material inflow. In addition, these additives effectively reduce cutterhead torque, increase TBM speed and reduce wear, as well as make soil manageable for transport. The formula used for these soil conditioners depends on the specific geology of the site. Often, a range of soil conditioners is recommended as the TBM technology develops.

Normet’s range of soil conditioning foams and polymers have been designed to meet the need of any geological location where excavation is being carried out. Typically, standard and polymerised conditioners are used for cohesionless soil, with the specific product used depending on the fines content, water pressures and the type of soil. By creating a compressible earth paste that completely fills and smooths out the pressure in the work chamber, polymerised foams bring cohesion back to coarse soils by binding together fines and water molecules and creating stronger foam bubbles. These polymers also provide a beneficial lubricating property, which reduces internal particle friction and general abrasive wear throughout the mucking system. Normet’s Tamsoil range includes standard foams TamSoil 190CF,TamSoil 191CF and TamSoil 195CF, along with polymerised foams and TamSoil 261CF/AW and TamSoil 265CF.

For clay and clay-like soils, TBM excavation will require an anti-clogging agent to prevent materials adhering to the cutting head or the conveyor system. Given the production problems associated with sticky clay formations, Normet has worked to develop a wide range of anti-clay agents to combat re-agglomeration, clogging and adhesion problems, including TamSoil 285AC,TamSoil 284AC and TamSoil 287AC. For hard rock TBMs, foam can provide the benefit of dust suppression and fighting tool wear, TamSoil 800AD, TamSoil 830AW and TamSoil 860AW have been specifically formulated to provide efficient hard rock tunnelling

As well as protecting and increasing the efficiency of the cutterhead and cutterhead tools, some sites require soil to be treated in order for it to be transported efficiently on the conveyor belts. When tunnelling through water-bearing ground, TBMs can use polymers such as TamSoil 500CP, which can be used in combination with soil conditioning foam when the conditioner alone cannot combat the increase in water content. Non aqueous polymer suspensions, such as TamSoil 700CP and 1000CP, which has been designed specifically for projects, can be injected into the working chamber or screw conveyor to create a watertight plug.

A persistent problem in hard rock TBM tunnelling is abrasion, high temperatures and dust accumulation. Typically, this is tackled by installing a sprinkler system, which both cools the cutterhead and reduces dust. However, many TBM projects, especially those dealing with particularly abrasive rock conditions, continue to experience disk cutter wear and dust-related blockages. Based on extensive fielding testing and laboratory trials at the Colorado School of Mines, Normet has formulated foaming anti-wear and anti-dust agents (TamSoil 800AD, 830AW and 860AW), which are applied through a rotary union and dedicated foam pipework to the cutterhead foam nozzles.

The most expensive and sensitive part of a TBM is the main bearing, so it is essential that it is protected. Main bearing sealing grease, such as Normet’s TamGrease BS1 excluder grease, is developed to have excellent adhesion and cohesion properties so that it can entirely fill the labyrinth of the main bearing and prevent soil, water or dust passing through the seals. Normet also offer TamGrease BL11 and TamGrease BL12, which are main bearing lubricant greases. Tail sealants are used at the other end of the TBM to prevent annulus grout, water or soil entering the invert area by forming an impermeable barrier together with the wire brush system. Not only do they need to be highly water-resistant and offer excellent adhesion the tail’s metal surface, it also needs to be pumpable. TamSeal TG91 has a special fibre composition to enable excellent flow and distribution inside the sealing chamber, as well as working well with the wire brushes, whereas TamSeal TG92 is pumped directly into the wire brushes before the TBM starts.

As shielded TBMs machine advance, they create a void known as the annulus gap. This area needs to be filled with grout or mortar to transfer the ground loads around the permanent structure and prevent settlement. Two component annulus grout or single component mortar is injected to fill the space between the soil and the segmental lining. Efficient grouting is essential for maximising uptime, completely embedding the lining to distribute pressure around the ring, and proving adequate protection. Normet’s TBM grout and mortar admixture range includes the TamCem R and 8BFG (standard retarders), 9BFG (retarder with latent accelerator), HCA (hydration control), as well as the TamShot 10SS (annulus grout accelerator). Other admixtures are also available dependent on the parameters required from the cementitious mixture.

For more information about Normet’s speciality chemicals for TBM tunnelling, or to purchase TBM technology for your site, visit their website.

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