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48
Geotechnical News • March 2014
www.geotechnicalnews.com
THE GROUT LINE
Contractual differences and
experiences
Underground project is generally
related to uncertainties, which a large
extent due to uncertainties in the
geological and hydrogeological condi-
tions. Especially grouting, it is dif-
ficult to predict how the work should
be carried out to a certain result will
achieved. This involves difficulties in
the preparation of tender documents
and provides a reasonable distribution
of risks (Brantberger, 2009).
Water inflow and related pre-grouting
works required to avoid settlements
and ground water draw down in the
vicinity of the tunnel is heavily influ-
encing the project cost and schedule.
Ignoring this fact and leaving these
issues as contractor risk and design
responsibility compensating water
inflow control as Lump Sum is the
ultimate way to cause program delay
and post project claims and disputes.
The regulation of the grouting works,
in Sweden, is normally done for the
amounts of the different steps in the
grouting process such as number of
drilling holes, number of probing,
establishment the equipment, cement
take and so on. The time of the grout-
ing is normally not regulated. Since
grouting time is not regulated and the
grouting work affects other tunneling
jobs, the grouting process will become
a time critical part of the tunneling
works.
The project owner needs to be directly
involved in control of water inflow
and costs associated with the efforts
to achieve the specified LRIR and
also draw on the experiences of the
contractor and the consultant. The
only way this can be secured is by
employing resources with relevant
experience with Project Specifications
for pre-grouting and install a coopera-
tion enabling decision taking at the
tunnel face. The PS shall define inflow
requirements for the different sections
in the tunnel. Drilling and grouting
equipment capacities and minimum
performance requirements shall be
defined in the PS as well as intended
material to be applied.
The two main differences between
Sweden and Norway regarding the
contracts are:
à
à
Reimbursement by the amount
of pumped cement, normal in
Sweden
à
à
Reimbursement by the hour and
the amount of pumped cement,
normal in Norway (Brantberger,
2009)
Trials have been conducted in Sweden
to get grouting contracts being paid by
the hour. One successful test was for
a 100 m long tunnel stretch in Törn-
skog tunnel. The contract was of type
partnering contract where the savings
in doing a better solution compared to
the standard method could be shared
by the contractor and the client.
The test was implanted with recent
research on grouting and became a
success (Brantberger, 2009). Another
trial that was abandoned at the desktop
was where the efficient grouting time
was introduced. The contractor should
only get reimburse for the predeter-
mined time per borehole spent on
grouting, not including borehole filling
Table 5. Forest Tunnels
Project
Depth (m)
Final pressure (MPa)
Stipulated ingress
Törnskogstunneln, Sweden
35
2.5
3 l/min/100 m
Kattleberg, Sweden
50
3
8 l/min/100 m
Björnböle, Sweden
60
5
7 l/min/100 m
Nygårdstunneln, Sweden
60
3
5 l/min/100 m
Baneheia, Norwegian
40
8
1.7 l/min/100 m
Bærum tunnel. Norway
Vary
10
2 l/min/100 m
Table 6. Urban Tunnels
Project
Depth (m)
Final pressure (MPa)
Stipulated ingress
Götatunneln; Sweden
40
3.5
0.7 l/min/100 m
Arbetstunnel Citybanan,
Sweden
35
2.5
7 l/min/100 m
Norra Länken, Sweden
30
3.5
4.5 l/min/100 m
Lundbytunneln, Sweden
15
2.5
2.5 l/min/100 m
Tåsentunneln, Norway
15
3.5
13 l/min/100 m
Svartdaltunne, Norway
10
2
<5 l/min/100 m
Storhaugtunneln, Norway
15
5
1.6 1/min/100 m