TECHNICAL | GROUND CONDITIONING
EPB / Mixshield Grain Size
Silt
100 90 80 70 60 50 40 30
Right, figure 4: Soil grading curves of selected EPB projects below groundwater
20 10
0 0.001 0.002 0.006
EPB Mode 0.02 0.06 2.0 6.0 20.0 60.0 Mixshield Mode Fine Medium Large Fine Sand Medium Large Fine
Gravel Medium
Large
BARCELONA 2003 Herrenknecht EPB Ø=12.06m 2.0 bar water pressure Foam + polymer + filler suspension
AVILES (ESP) 1999
Lovat EPB Ø=3.4m
2.5 bar seawater Foam + polymer
TOULOUSE (F) 2003 HK EPB Ø=7.72m
Mainly underwater table Foam + anti-clay
MAILANO (I) 1994
NFM EPB Ø=8.03m
Mainly above GW Foam + polymer
TORINO (I) 2004 Lovat EPB Ø=7.7m
Mainly above water table Foam + polymer
LYON (F) 1996
NFM EPB Ø=10.98m 1.5-3 bar water Foam + polymer + bent
BOTLEK (NL) 1999 HK EPB
Ø=9.76m 3.6 bar water Foam + polymer
Aviles (1999)
Again, a challenging jobsite: a sewer outfall project, tunnelling with a Lovat EPB-TBM first through clay soil and afterwards through gravelly sand with absolutely no silt content (sharp graded sand with 20% gravel, see Figure 4), all below the Atlantic Ocean off the coast of northern Spain. After having difficulties with clay clogging (the anti-
clay polymers were not ready at that time) and injecting a lot of water, the soil changed suddenly, and much earlier than had been foreseen, into running sand under 3.5 bar sea-water pressure. The tunnel was almost flooded. Our first proposal at the time was to inject a
bentonite suspension at the cutterhead to increase the soil cohesion. But due to a very long installation time and huge additional investment necessary the contractor asked to use whatever chemical was necessary to solve the problem. Finally, we composed a foam/long chain polymer mix with much higher polymer content than ever used to create a strong and thixotropic foam that was able to replace the water in soil voids. Figures 5 & 6 illustrate well the difference between using a simple foam and using a well adopted polymer/foam mixture, resulting in excavation of an almost dry sand. The project was finished very successfully (Langmaack 2005, Langmaack 2016).
12 | November 2023
Madrid MetroSur (2001) From 2000 onwards Madrid had a complete infrastructure development plan, including a metro system for the south of the city. Unfortunately, the soil in the south of the capital
consists mainly of clay, which results in heavy clogging on a cutterhead and inside the working chamber (Langmaack 2002). Using the foams available at that time, the 9.33m-diameter EPB machines on the MetroSur project achieved only very low advance rates of about 5mm-10mm/min and additional heavy maintenance and cleaning of the cutterhead and the working chamber. This difficulty jeopardised the plan. However, the problem lead to a new way of using
foams and anti-clay polymers together. For the first time they were very successfully applied on-site and since then the approach has been used all over the world, being copied by others. On the MetroSur project, the effect of the new way of using foams and anti- clay polymers together was dramatic, as illustrated by Figures 7 & 8 – even making tunnelling records possible, achieving of 936m in 31 days, with the same TBMs at the very same location where the machines had struggled.
This was a big step forward for the EPB use in clay, and we were extremely happy. A special thanks to Rafael Valenzuela and Daniel Montalban who supported me with great enthusiasm on site.
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