Civil Engineering Reference
In-Depth Information
with:
m
reduction of boring progress due to wear [-]
T
time required to drive a tunnel section
F
thrust force per disc cutter [t]
m
1
base value for the reduction of boring progress due to wear [-]
D
tunnel diameter [m]
CLI Cutter Life Index, a specific wear parameter of disc cutters determined from labora-
tory tests [-]
q
concentration of quarzite in the rock [%]
n
rock porosity [%]
γ rock density [kg/dm³]
Figure 2-26
Wear index
CLI depending on the rock
type [13].
Classification according to cuttability and abrasiveness.
A simple excavation classi-
fication is not adequate for TBM tunnelling. Parameters that determine penetration are
therefore necessary for the overall grading of the rock mass to be bored.
Such a classification can be performed directly through the description of the geological stra-
tum or through the direct determination of penetration using test strokes, as with SIA 198.
The two classifications of the rock mass that can determine the performance of a TBM
were recognised in 1974 by Rutschmann [194]. In order to determine the cuttability, he
considered four factors decisive:
- Stress-strain relationship: E modulus at 50 % compression strength
E
t 50
.
- Uniaxial cylinder compression strength b
D
.
- Brazilian tension strength b
Z
.
- Hardness, for example the saw hardness
SH
.
The rock mass classification according to Rutschmann essentially describes the possibil-
ity of bracing a TBM. Both classifications correspond to tests of a qualitative description.
Rauscher developed a classification system based on models of the cuttability of a rock
mass. This cuttability is expressed as an analytic relationship between the independent vari-
able
F
V
(thrust force) and the dependent variable
N
B
(power of the cutterhead drive) and
v
n
(net boring speed). Using this relationship, he produced a nomogram that enables the clas-
sification of different rock mass types (Fig. 2-27). In the nomogram, the different cutting
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