GROUND CONDITIONING | TECHNICAL
soil to highly permeable and cohesionless gravelly soil. Figure 4 (Langmaack 2008) illustrates the soil grading curves of several selected EPB-TBM projects below groundwater level. The milestones in ground conditioning development
with EPBMs in Europe are illustrated by several key projects.
Lyon (1997) After a fairly challenging first European EPB-TBM use in Milan, in 1994, with unadopted Japanese foam in very coarse soil (Greeman 1994), the first larger diameter EPB project in Europe was BPNL Lyon in France, from 1994-1998. For the works, Bouygues operated an 11.02m-diameter EPB shield manufactured by French company NFM. It was the world’s biggest EPBM at the time. For the project, two tubes were driven through 1,250m of rock in open mode, a 450m-long transition zone of rock/alluvium in EPB closed mode, and then bored through 1,552m of coarse soil. The latter geology is still nowadays considered to be ‘not usable for EPB machines’ even though the TBM drive was realised quite successfully. As described by Langmaack (1997), for the first time
different soil conditioning foams were thoroughly tested. In addition, the first liquid biological long chain polymers were developed to give structure to the muck and modify the foam behaviour. The product development around this jobsite was the germ cell for the modern foams, polymers as well as anti-clay additives, whereas the latter still needed some re-design to be efficient for site use, finally, in 2001. For the BPNL jobsite, a couple of initial tests were
driven, tests which are still used for actual projects: ● Different foams for different geologies ● Foam behaviour with and without polymer ● Permeability studies with foam, foam + polymer, foam + polymer + bentonite suspension to modify soil with permeability of k=2.7 x10-3 m/s together with the original soil
m/s down to 4.5x10-5 Top and centre, figure 2: Figure 4 illustrates the BPNL soil grading.
The author would like to thank Laurent Frouin and Fabrice Grandhaie in this context for all the inspiration. It was a truly a great time.
Robbins soft ground TBM on Paris RER transport tunnels, in mid-1960s PHOTO CREDIT: ROBBINS
Bottom, figure 3:
First EPB-TBM design studies in the mid-1960s, in Japan PHOTO CREDIT: SATO KOGYO CO
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