Engineering geology aspects for design and classification - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 88

The general special features described by the ETB, which have already been described in
Section 2.4.3.1, are also applicable here according to the ETB.
The following special features for TBM tunnels are listed:
- Recording of the quantities of the type and extent of support measures in ranges (shot-
crete thicknesses, rock bolt number and length, type of arch, spacing, type of rein-
forcement, single or two layers; a certain overlapping of ranges of adjacent tunnelling
classes is suitable according to the DGGT).
- Installation location and installation sequence of support in the machine area, backup
or rearward area.
- Cuttability of the rock (mineral compositions - particularly quartz content), mineral forma-
tion, mineral grain size, compression strength, hardness, abrasiveness, jointing structure.
- Grading by given net boring speeds.
- Consideration of the special features of shafts.
The following special features for shield machines are listed:
- Grading distribution, fines content, mineral composition, bedding density, consistency,
water content, groundwater table.
- Special features, which could obstruct the advance rate, like mineral-chemical cementa-
tion, adhesiveness, soil plasticity, influence of water content in changing the soil, boul-
ders, intercalated hard layers, high/very variable permeability, separation in the machine
area (not due to machine).
- Measures to maintain the stability of the face, interventions in front of the cutting wheel.
- Removal of obstructions.
- Type of annular gap grouting with regard to obstruction of advance.
- Restrictions due to building or facilities with shallow overburden.
- Consideration of measures ahead of the face like probing the ground from the machine
and/or ground improvement from the machine (grouting or freezing).
2.5.6.2 Classification in Switzerland
SIA 198 “Underground Structures”, issue 1993, reissue 2004 [218]. The basics of this
standard are described in Section 2.4.3.2 (page 57).
Section 5.4 of the standard is about payment for excavation works with a TBM in hard
rock and is based on the idea that costs are directly related to the type and extent of neces-
sary support works, but also the point in time when the measures have to become effective.
In Switzerland, tunnelling classes are defined by SIA 198 (1993) based on the costs of
tunnelling. Excavation types A (full face) and E (excavation in phases with a pilot tunnel
or pilot shaft and subsequent enlargement; both with TBM) are differentiated. The sub-
sequently explained provisions apply to both of these excavation types. If a pilot tunnel
bored by a TBM is combined with enlargement using another method of excavation, the
relevant provisions for bored tunnels apply to the pilot tunnel and those for drill and blast
or roadheader excavation as appropriate apply for the enlargement.
The tunnelling classes result from a combination of excavation and tunnelling classes. The
excavation classes are based, as in Germany or Austria, on the required support measures
and the installation location along the TBM. Five excavation classes are normally differenti-
ated, with no support measures being intended for the rock mass in excavation class 1 and