Civil Engineering Reference
In-Depth Information
The abrasiveness of rock has a direct effect on the cost of tunnelling. A limited and indirect
influence results from the increased proportion of cutter changing time and any interrup-
tions for the changing of wearing parts like lips or buckets. A wear class in addition to
cuttability could therefore be suitable for the payment of wear, but scarcely for rock mass
classification as a basis for advance performance.
Classification according to the type, extent and installation location of the necessary
support measures and bracing feasibility.
An experienced tunneller is normally capable,
with intense discussion with the geologists, of undertaking a classification according to the
type, extent and installation location of support measures. He compares the information
gained with the facts from similar completed structures or with knowledge of any differ-
ences from projects that used similar construction methods. Whether this achieves better
results than a classification according to rock mass properties is questionable. A better
procedure would be to check the results of a classification according to rock mass proper-
ties against experience.
The determination of the necessary extent of temporary support including the compulsory
addition of a safety margin for the miners is undoubtedly only possible at the face after
excavation.
The national standards in Germany, Switzerland and Austria all recognise this as they are
based on the extent of temporary support.
All are however based on the classification for drill and blast tunnelling without consid-
eration of the fact that certain support measures cannot be used at any location in a TBM
tunnel. For example shotcrete applied in the machine area is still included as a classifica-
tion factor.
Without exception, these classifications provide no support measures in the first class,
corresponding to a stable rock mass. The bodies responsible for insurance, SUVA, TBG,
AUVA, however, demand head protection from a profile height more than 3 m. If accord-
ing to the definition the installed support forms the basis for classification, it is immaterial
for what reason it is necessary. It thus determines the class in every case.
2.5.6
Standards, guidelines and recommendations
2.5.6.1 Classification in Germany
DIN 18312 VOB Part C “General technical contract conditions for construction works
- Tunnelling”, issue 12/2002 [59]. The basics of this standard are described in Section
2.4.3.1. Regarding mechanised tunnelling, the standard provides sub-classes TBM 1 to
TBM 5 (Table 2-29) for tunnel boring machines and classes SM 1 to SM 3 (Table 2-30) for
shield machines. For TBM drives, the tunnelling classes are differentiated according to:
- required support,
- obstruction of mechanical excavation,
- requires support installation in the machine area and
- special measures.
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