Engineering geology aspects for design and classification - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 48

Table 2-15 Values for the ESR depending on the intended use.

Exca vation category ESR

A temporary excavations 3 to 5

B shafts with a round cross-section 2.5

shafts with a rectangular cross-section 2.0

C permanent excavations, unpressurised water tunnels for hydropower systems, pilot

tunnels, headings and directional tunnels for large excavations

1.6

D storage caverns, water treatment works, smaller road and rail tunnels, surge tanks and

access adits

1.3

E power stations, large motorway and rail tunnels, civil protection bunkers, portal areas,

connections between tunnels

1.0

F underground atomic power stations, railway stations, factories 0.8

The ESR relates to the use of the excavated cavity and the required degree of safety, see
also Table 2-15.
The relationship between the Q index and the reference parameter for the support deter-
mines the appropriate support measures. For temporary support, either the Q value is in-
creased to 5 or the ESR to 1.5 ESR , if the temporary support is intended for a period of less
than one year. The ESR can be reduced to 0.5 for long transport tunnels. It should be noted
that the required anchor length is determined as follows, with B being the excavated width:

= +·

2 0.15 B

L

ESR

5 2

The maximum unsupported round length (unsupported) = 2 ESRQ

The relationship between the Q value and the permanent support pressure P can be deter-
mined from the following formula:

= 2.0
r

1

P

J

3

Q

In case the number of joint sets is less than three, the formula can be expressed as follows:

= 2
3

11
3

P J

n

J

Q

r

2.4.2.4 RMR System (Rock Mass Rating System)
The RMR system [23, 230, 22] is mainly used in countries with American influence. It was
essentially developed by Z. T. Bieniawski in the years 1972 and 1973. The system can also
be referred to as the “Rock Mass Rating System” or also as “Geomechanics Classifica-
tion”. Over the last twenty years, the system has been confirmed in over 350 practical ap-
plications and has been continuously improved with supplements. The RMR system, like
the Q system, is a quantitative classification system, which is calibrated from completed
projects and is thus continuously improved.