TECHNICAL | MECHANISED TUNNELLING


MTBM can move even when the friction load on the


pipe is too high, or the pipes reach their jacking capacity. Also, for longer drives, a telescopic station can


be used, helping to maximise thrust loads but also sensitively control machine advancement without overloading the cutting wheel tools. A telescopic station consists of a ring of hydraulic cylinders directly behind the cans, enabling the frictional loads of the MTBM to be separated from the tunnel alignment. Jacking pipes need to be strong enough to transfer


all jacking loads to the MTBM at the front end of the pipe string. Various types of jacking pipe materials are used, including steel, reinforced concrete (RCP) and reinforced plastic (FRP). Pipe joints also transfer jacking loads, from pipe to pipe, and so are a further critical component – especially in curved alignments where only part of the pipe cross-section transfers the thrust load.


Bentonite lubrication in hard rock Control of the skin friction is a key factor for hard rock pipejacking project success, and, as such, special attention is paid to bentonite lubrication. The longer the drive or the larger the diameter, the more the focus is on lubrication. Uncontrolled distribution of bentonite along the tunnel route or tearing of the lubrication film can lead to a significant increase in jacking forces. For continuous lubrication, Herrenknecht has


developed an automated volume-controlled bentonite


Above, figure 9: Cutting wheel of the AVN 800 HR after breakthrough in Hong Kong


Right, figure 10: Breakthrough on 1,216m long drive 2 of Hunua 4 watermain project in New Zealand PHOTO CREDIT: MCCONNELL DOWELL CONSTRUCTORS LTD


28 | January 2024


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