Dewatering, waterproofing and drainage - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 201

Figure 5-9 Extent of
obstruction by ground-
water (rock mass type C2
according to ÖNorm B
2203 [170]).
Figure 5-10 Average
advance rate for rock
mass types B1 and C2
depending on quantity of
groundwater [120].
5.2.3.3 Influence of groundwater on tunnelling costs
In addition to the effect on the advance rate, groundwater also has a drastic effect on over-
all tunnelling costs. The factors that influence costs are as follows:
Machinery costs. The slower advance rate with water ingress increases the average ma-
chine time per metre of tunnel advance. Worse machine wear and higher repair costs also
have to be expected. Pumps, for example, have to be considered as additional machinery.
Material costs. In addition to the increased shotcrete consumption due to increased re-
bound, the materials for dewatering measures of drainage and waterproofing also have to
be considering.
Personnel costs. Due to the significantly worsened working conditions with water ingress,
reduced performance has to be expected. The various obstructions caused by water also slow
the advance rate, which increases the personnel costs per metre of tunnel advance. The pro-
portion of personnel costs amounts to about 40 % of overall cost and is also a decisive factor
for the extra costs due to water and can be up to 60 % more than the original proportion.
5.2.4 Environmental impact and cleaning
The environmental impact of construction works is becoming ever more significant due
to increased environmental awareness. In order to avoid any possible criticism of tunnel
construction, which can actually be described as “environmentally friendly”, the effects
on the surrounding groundwater should be paid great attention.