Engineering geology aspects for design and classification - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 52

2.4.3 Standards, guidelines and recommendations
The classification becoming established in German-speaking countries today is based on
a classification of the rock mass as a construction material and its behaviour when the
tunnel is excavated and supported. The main emphasis is placed on systematic grading of
the works that determine performance of tunnelling and support. The influence on time
is also considered in order to quantify obstructions. In newer guidelines, rock mass and
support are generally collected into tunnelling classes, which are based on all works with
an influence on the advance rate. Detailed, quantified classification is reserved for the
project-related tunnelling classification.
In Austria [173], classification is carried out according to the excavation and support
works that determine the advance rate, like type of excavation and round length dif-
ferentiated according to top heading, bench and invert; and type, extent and installation
location of support, depending on the rock mass behaviour to be expected as the tunnel
is driven.
In Switzerland, classification is also carried out according to the excavation and support
works that determine the advance rate. The behaviour of the rock mass as the tunnel is
driven is considered, as in Germany, without additional direct assignment of rock mass
types through the type of excavation depending on rock mass and type and extent of sup-
port [218].
The classification systems in Austria and in Switzerland can be directly transferred into a
project-related classification through the numbered grading of the round lengths and the
support in the normal case.
Special features in the standards, guidelines and recommendations related to mechanised
tunnelling are dealt with in Section 2.5.6.
2.4.3.1 Classification in Germany
DIN 18312 VOB Part C “General technical contract conditions for construction
works - Tunnelling”, issue 12/2002 [59]. Tunnelling classification for tunnel construc-
tion projects is regulated by the DIN 18312 VOB Part C 2002-12 in Germany. The contract
classification according to this standard makes the assumption that the cross-sectional size
and shape of the cavity and the construction process and excavation and support measures
are specified and the grading of soil and rock into the individual classes is only undertaken
in compliance with these specified data.
In the very generalised tunnelling classification, classes 1 to 7A are differentiated for
conventional tunnelling according to the extent of support work and the resulting ob-
struction or delay to the advance (Table 2-20), and for tunnel boring machine drives the
classes TBM 1 to 5 (Table 2-29) and for shield machine drives the classes SM 1 to 3
(Table 2-30). The special features of mechanised tunnel drives are explained in Section
2.5.6.1.