ABSTRACT
In hydroshield tunnelling, a slurry of activated bentonite is used to support the tunnel face and remove the cuttings. To permit the reuse of this slurry and to preserve its rheological properties, the cuttings must be separated out of the slurry and the slurry density readjusted with addition of bentonite. Problems are frequently encountered, however, when the tunnel is driven through extremely clayey soils as their particle size distribution overlaps with that of the bentonite so that the separated material still contains a residual quantity of bentonite. The elements of this control system consist of sensors for measuring the operating state, a process control computer for recording and processing the measured data, and the activator, in this case a control valve downstream from the overflow collector of the hydrocyclone battery. The new technological elements of the Westerschelde Regeneration plant represent an important step forward to a save bentonite regeneration under complicated and varying feed conditions.
