DAUB recommendations for the selection of tunnelling machines - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 367

Geotechnical report Description of the site investigation with characteristic values for
the rock and rock mass parameters according to DIN 4020 Number 10.
Gripper Side-mounted, radially acting bracing apparatus in hard rock tunnel boring ma-
chines, intended to transfer the thrust forces into the surrounding rock mass, resist rolling
and stabilise the TBM.
Ground behaviour Behaviour of the unsupported ground at the face and also at the sides
of a tunnel without consideration of the construction process.
Ground profile Geometrical assumptions about the profile of natural formations or strata
(DIN 4020 Appendix C2) or of homogeneous zones.
LCPC abrasiveness coefficient (ABR) Value from the test of the same name for the
characterisation of the abrasiveness of soft ground or broken rock, named after the “Labo-
ratoire Central des Ponts et Chaussées”.
Liquefaction Loss of the shear strength of a soil due to positive pore water pressure.
Mechanical face support Support of the face with breasting plates.
Open mode In open mode, the excavation chamber is not under pressure.
Overcut Differential dimension between the bored radius and the shield radius measured
at the shield blade. The overcut serves e.g. to improve driving round curves, to reduce the
skin friction and relieve stress on the ground.
Primary wear Wear on the excavation tools solely due the excavation of the face; influ-
enced by the strength, jointing and abrasiveness of the rock mass.
RMR Rock Mass Rating: Value for the classification of rock mass based on 6 rock mass
parameters.
Rock mass behaviour Behaviour of the unsupported cavity in hard rock (referred to as
ground behaviour in soft ground). The rock mass behaviour is determined by the proper-
ties of the rock and the jointing structure, the stress and formation water situation and the
shape and size of the excavated cavity.
RQD index Rock Quality Designation index: value for the characterisation of rock quality
based on the sum of the lengths of drill core pieces larger than 10 cm out of the total length
of core taken according to ASTM D6032-02.
Surcharging Provision of an additional loading on the ground through e.g. filling above
sections of tunnel with shallow overburden.
Secondary wear Secondary wear results from the rubbing and grinding action of the
already excavated ground. Poor material flow and sticking increase the secondary wear.
Separation Description for the separation of fluid and solid in hydraulic material transport.
Stability Stability describes the stability of the ground including consideration of thee ef-
fect of the construction process. The stability is verified with calculations.
Standup time of the ground The length of time the ground can stand up without support.
The verification through calculation of the stability of the face and sides of the excavation
remain, however, decisive for the final evaluation and selection of the tunnelling machine.