Civil Engineering Reference
In-Depth Information
10.5
Target process structure
How should the decision be reached, whether a process is “running well” or not? How can
the target performance be quantitatively or qualitatively defined for the individual partial pro-
cesses? Different methods are used for the various partial processes as shown in Table 10-1.
FEM simulation of the shield advance is an important tool for the determination of the
design specification and also serves to verify the actual system behaviour through “ back
analyses”. With the assistance of FEM simulation, it is possible with the current state of
the technology to display the extremely complicated interactions between ground and tun-
nelling machine. The FEM simulation can be structured into the following phases:
- Geometrical and process-technical modelling with realistic discretisation of all ma-
chine elements (face support, shield gap grouting, shield tail grouting etc.),
- material modelling with the selection of a suitable constitutive law (consideration of
positive pore water pressures, creep effects, non-linear-elastic behaviour etc.),
- step-by-step analysis to consider the effects of different phases of construction on the
stress state in the ground,
- verification of the results and plausibility checking.
Table 10-1
Procedure for the determination of the KPIs/Key Performance Indicators
Partial process
Intended process analysis
KPIs
analytic calculation model of
cuttability (balance of forces),
structural calculation model
based on laboratory tests
contact force, torque, penetration,
skin friction, material density,
cuttability index
Ground excavation
(tool wear)
FEM simulation, kinematic
support pressure calculation,
analytic calculation model for
volume control
support pressure, suspension losses,
foam injection pressure, density
distribution
Face support
FEM simulation of the hydrau-
lic processes, analytical calcula-
tion models
support pressure distribution, foam
injection pressure, foam parameters
Soil conditioning
FEM simulation, analytical
calculation models
Grout volume under consideration of
the overbreak, grouting pressure
Annular gap grouting
analytical calculation model
(consistency development, haz-
ardous materials calculations)
liquidity index, carbon content,-
tenside/polymer concentration
Soil tipping
Suspension densities, solids con-
tent, viscosity measurements, yield
strength
Soil separation
analytical calculation models
Fig. 10-4 shows the 3D modelling of a shield tunnelling machine in the surrounding
ground. The excavation chamber, shield area, annular gap grouting and segmental lin-
ing can be recognised. The model is designed so that all measured technical machine
parameters, for example the support pressure at the working face, support pressure in the
annular gap or the “volume loss” through overcut at the shield skin are taken into account.
With this procedure, it would theoretically be possible to import measured machine data
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