Civil Engineering Reference
In-Depth Information
contact force and the cutting wheel torque increase over-proportionately with increasing
support pressure. The flow behaviour of the excavated muck can be improved with suitable
conditioning agents like e.g. bentonite, polymers or foam. Soil conditioning with foam is
recommended for active support pressure control and to ensure low settlement outside the
predestined area of application.
Earth pressure balance shields have the advantage that operation is possible without modify-
ing the process technology with partially filled and unpressurised excavation chamber in open
mode (SM-V5-OM) without active face support. It should be noted that in this case the cutting
wheel and screw conveyor combination will grind the excavated soil/rock considerably more
than with a conveyor belt through the centre (SM-V1). If the soil tends to sticking, hindrance
and increased wear have to be reckoned with. In order to improve the material flow and reduce
the tendency to stick, conditioning agents should be used. Particularly unfavourable for earth
pressure balance shields, both in soft ground and in rock, is a combination of high support
pressure, high permeability, high abrasiveness and difficulty in breaking the grain structure.
11.9.2.8 SM-T1 (partial excavation, face without support)
This type of machine can be used above the groundwater table if the face is sufficiently
stable, see here SM-V1.
Partial machines always offer good access to the face, so the process can be very advanta-
geous if obstructions are to be expected.
11.9.2.9 SM-T2 (partial excavation, face with mechanical support)
This type of machine can be used when the support provided by material piling on the
platforms at its natural angle of repose is sufficient for tunnelling with a limited degree of
settlement control. Breasting plates can be installed for additional support in the crown
and on the platforms. The main area of application is weakly to non-cohesive gravel-sand
soils above the groundwater table with the corresponding angle of friction.
11.9.2.10 SM-T3 (partial excavation, face with compressed air application)
The use of this type of machine is appropriate when types SM-T1 and -T2 are to be used in
the groundwater. The entire working area, including the already completed tunnel or just
the working chamber, is pressurised.
11.9.2.11 SM-T4 (Partial excavation, face with slurry support)
Partial excavation machines with slurry-filled excavation chamber are no longer used.
11.9.2.12 KSM (Convertible shield machines)
Convertible machines combine the areas of application of each machine type in changeable
ground conditions. Their area of application is therefore extended to both sets of criteria.
The number of conversions from one tunnelling process to another should be kept as low
as possible, as rebuilding takes a long time and is expensive.
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