Engineering geology aspects for design and classification - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 85

Table 2-29 Tunnelling classes for tunnel boring machines (TBM) [59].

Tunnelling class Type of excavation

TBM 1 Excavation without support

TBM 2 Excavation with support, the installation of which does not obstruct excavation

TBM 3 Excavation with support immediately behind the machine or already in the

machine area, the installation of which does not obstruct excavation

TBM 4 Excavation with support in machine area immediately behind the cutterhead, with

excavation having to be interrupted to install it

TBM 5 Excavation with measures of a special nature, with excavation having to be inter-

rupted to carry them out

While no support is necessary in the most favourable tunnelling class TBM 1, increasing
instability of the rock mass and rising tunnelling class lead to the obstruction of boring by
support measures, or boring even has to be interrupted. In tunnelling class TBM 5, special
measures are necessary, for example for bracing the machine, to remove fallen debris in
the machine area, to probe the ground and/or to improve the ground.
The classes reflect the installation location, with machine area and backup or rearward
areas being differentiated. This classification is only general, as the standard does not pro-
vide any sub-classes or detailed explanations. Only in Section 3 “Construction” is there a
note regarding excavation and support that all measures to be undertaken are a matter for
the employer unless special contractual agreements have been specified about their type
and extent.
For shield machines, the classes SM 1 to SM 3 are defined (Table 2-30). There is no de-
lineation of the two systems, tunnel boring machine and shield machine.

Table 2-30 Tunnelling classes for shield machines [59].

Tunnelling class Excavation type

SM 1 Excavation without support to the face

SM 2 Excavation with partial support to the face

SM 3 Excavation with full support to the face

Recommendations of the “Tunnelling” working group of the German Society for
Geotechnics (DGGT) (ETB) [52] The “Tunnelling” working group recommends the gen-
eral classification scheme from DIN 18312, which is intended to serve as the basis for a
project-specific classification for each tunnel. In addition to the classes from DIN 18312,
TBM 1 to TBM 5 and SM 1 to SM 3, the additional classes SM-V1 to SM-V5 are also
defined for shield machines with full-face excavation (Table 2-31).