Both bores on the Westerschelde traffic tunnel project under the west Schelde in the southern Netherlands are progressing well following the delays mainly due to excessive reaction to ground pressures at the deepest part of the drives (T&TI October).
The most badly affected of the two Herrenknecht Mixshield TBMs, on the east drive, is now 1.8km (837 segmental lining rings) in on its 6.6km run from Ternuezen northwards, whilst the west drive, which started three months later, has now progressed 2km. At the time of a T&TI site visit at the beginning of November, average advance rates were 14 rings/day for both drives.
Distortion to the east TBM shield can has not affected steering performance the KMW design-and-construct contracting JV reports.
The project now stands about nine months behind schedule.
Much of the delay was taken up by the need to employ offshore diving teams working under saturation conditions to change the peripheral cutters on both TBM cutterheads as well as recovering the shields from squeezing conditions in glauconite-carrying sands. Now both TBMs are cutting through self supporting Boom Clay.
Meanwhile work is progressing on the first two crosscuts between two drives that will provide escape routes for tunnel customers. Local ground freezing within brine is being used to secure the surrounding ground before excavating the drives with a boom-cutter mounted on a mini-excavator and providing a primary lining of shotcrete. one crosscut is in the glauconite sand and the other in clay, allowing performances in both main ground conditions to be studied.
