Influence of Clogging on the Muck Transport in Shield Machines

Schematic presentation of walls of clogged material or compacted clogged material given varying shield driving methods (upper row: profile section at tunnel axis, centre row: overview, lower row: cross-section roughly 0.5 m in front of the pressure wall resp. submerged wall)

Clogging diagram according to Hollmann & Thewes (2013) with changes in consistency of the excavated material owing to underground water in the case of an open-mode shield drive

Left: Clogged material with plastic consistency. Centre: sample of solid compacted clogged material from an open-mode shield drive. Right: stiff clogged matrix with pressed gravel components from a hydroshield drive

Wall-like compacted clogged material between completely extended screw conveyor and cutting wheel

Left: View from the face through the cutting wheel aperture of the wall of compacted clogged material as an “obstacle” in front of the screw conveyor aperture. Centre: comparative photo prior to the start of the drive showing a view through the cutting wheel aperture towards the screw conveyor. Right: subsequently installed cleaning arm

Left: Transfer funnel within the muck ring with walls of compacted clogged material at the edge. Centre: comparative photo with view of the cleaned transfer funnel. Right: cleaning the transfer funnel at the interior of the muck ring

Excavation chamber with compressed air access with the slurry half-lowered: left: cleaning arm with deep indentation. Right: removal of the outer cleaning arms

Excavation chamber with compressed air access with the slurry completely lowered: left: wall of clogged material covered with slurry residues along the shield cutting edge above the flushing nozzles (direction of flushing in the floor area: red arrow). Right: residues of the wall of clogged material with an internal set-up of gravel and stone components in a stiff clogged matrix during cleaning operations

Excavation chamber with compressed air access with the slurry completely lowered: wall of clogged material in front of submerged wall aperture (crest of wall between the red lines) and accumulated excavated material behind with residual slurry. One of the walls of clogged material can be seen indistinctly at the shield’s cutting edge in the background (crest of wall between blue lines). A green arrow indicates the operating direction of a flushing nozzle

Schematic presentation for the formation of walls of clogged material /red: clogged material, yellow: gravel and stone components): 1a to 3a: section at the height of the flushing nozzle through the side walls of clogged material at the shield’s cutting edge. 1b to 3b: view against the direction of driving of the submerged wall with wall of clogged material in front of the baffle aperture and the formations at the side at the shield’s cutting edge

Shield drives in fine-grained clayey soil are frequently affected by clogging. Walls of clogged material represent a special form of this particular obstacle. Such walls can attain a high degree of strength and develop directly in the TBM’s material flow. The fact that these walls of clogged material exacerbate or even interrupt the direct path of the excavated material from the rear side of the cutting wheel to the follow-up conveying system makes driving especially difficult (Fig. 1).

Conveyance of the excavated material from the cutting wheel towards the rear must therefore be carried out by a circuitous route with the material first being lifted by the cutting wheel and then transferred upwards. From there it moves backwards in the excavation chamber over the top of the walls of clogged material towards the suction inlet or in the case of the open mode EPB shield, towards the screw opening.

Such phenomena have been observed both in the case of unsupported open-mode EPB drives as well as in fluid-supported slurry shields, where the excavated material has to be transferred...

Influence of Clogging on the Muck Transport in Shield Machines

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