Engineering geology aspects for design and classification - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 50

Table 2-16 continued

Parameter Range of values

5 Ground-

water

Inflow
per 10 m
tunnel
length
[l/min]

none or < 10 or 10 - 25 or 25 - 125 or > 125 or

Joint
water
pressure
to
principal
stress

0 or < 0.1 or 0.1 - 0.2

or

0.2 - 0.5 or 0.5 or

General
condition

completely
dry

damp wet drips streaming

Rating 15 10 7 4 0

Table 2-17 Evaluation correction for the strike direction of the fault.

Strike and dip direction of
the fault

Specially
favourable

Favourable Acceptable Unfavo-

urable

Very unfa-
vourable

Evaluations Tunnels and

mines

0 up to 2 up to 5 up to 10 up to 12

Foundations 0 up to 2 up to 7 up to 15 up to 25

Slopes 0 up to 5 up to 25 up to 50 up to 60

If the results of the two tables are added, this gives a characteristic value, which enables
assignment to a rock mass class with the aid of Table 2-18. The higher this value is, the
better is the prevailing rock. The added range of values lies between 0 and 100, bad to
very good.
In Table 2-19, the practical evaluation of the individual rock mass classes is explained us-
ing examples from engineering practice. Since the rock mass consists of the most varied
sections, those with the most unfavourable faults for the future structure are decisive. Fu-
ture construction measures have to be planned for this section, although the situation with
regard to rock strength and other parameters may be good. In case two sections with dif-
ferent parameters dominate the entire cross-section, the evaluation numbers are weighted
according to their area of occurrence and averaged to one characteristic value.

Table 2-18 Determination of rock mass classes from the overall evaluation.

Evaluation 100 - 81 80 - 61 60 - 41 40 - 21 < 20

Rock mass class I II III IV V

Description very good rock good rock acceptable rock bad rock very bad rock