Dewatering, waterproofing and drainage - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 193

Table 5-8 Sample table of reduction factors for water obstruction [170].

Obs-
truc-
tion
clas-
ses

Favourable Medium Unfavourable Very unfavourable

1 2 3 4

min. max. min. max. min. max. min. max.

l/s days % % % days % % % days % % % days % % %

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17)

0.5
to 2

n n n n n n n n

over
2
to 5

n n n n

over
5
to 10
over
10
to 20
over
20
to 40
over
40
REMARKS:
Working days and min./max. reduction factors are to be given by the client for the specific project,
depending on the formation water quantity and water obstruction classes. The reduction factors to be
given by the contractor must be higher for unfavourable combinations than for favourable combina-
tions. A reduction of 20 % means that the advance rate under the conditions of water obstruction is
only 80 % of the advance rate without water obstruction

Proposal for quantity measurement. For excavation and support works, the water should
be measured about 100 m behind the face, or the relevant advance location. The total water
quantity should also be measured at the start of the excavation of the round (Fig. 5-3). It
is assumed here that cost of excavation and support obstructions is determined from the
water quantities about 10 m behind the relevant advance location (top heading or bench).
Water ingress is measured in l/s. Limit values should be given in the specification for vari-
ous degrees of obstruction, sub-divided according to the different geological conditions
and their effect on the obstructions.