Civil Engineering Reference
In-Depth Information
This prospect of a bonus turned out to be extremely effective and by taking
additional measures the speed of the boring process and the fitting out work
went ahead by leaps and bounds.The tunnel was eventually put into opera-
tion on 14th March 2003, 8 months earlier than was agreed in the package deal.
Positive incentive works better than a penalty
The conclusion would seem justified that the introduction of a continuous
positive incentive in the form of a bonus payment has a much greater effect
on the progress of a project than if there is only a (limited) penalty arrange-
ment. However, for the client it is not always easy to assess what a feasible
plan is and to determine within what period such a project can be reason-
ably realized. There was hardly any experience with bored tunnels in the
Netherlands, and although many projects had already been carried out
abroad, these experiences could not be copied exactly: each project has its
own specific circumstances and therefore no hard statements could be
made about the boring speeds to be realized.
Until the date on which the package deal was concluded, much less progress
was made than the previously expected 12 metres per day and nothing indi-
cated that this production rate would suddenly go ahead by leaps and bounds.
The completion date of 15th November 2003 therefore seemed to be very real-
istic.The fact that the contractor was able to complete the project much earlier
is chiefly due to logistical and organizational measures: there was still an awful
lot that could be optimized, however, not without considerable investments.
Not only were delays as a result of logistical problems solved to a large extent,
also the introduction of a competitive element and a remuneration system
within the building consortium certainly improved the boring process.
External quality assurance
Monitoring versus supervision
The quality of the way in which the construction of a tunnel is carried out
and the quality of the construction itself are of enormous importance for the
final result. The building in of tunnel rings, for example is an irreversible
process. Once part of the lining, the segments can no longer be removed and
replaced, even though this might well be desirable, for example because of
damage.
The stipulation was included in the contract that the contractor would carry
out the project subject to quality assurance and with this would check
and control the quality of its own working method and of its products. The
idea behind external quality assurance is that the client can monitor the
implementation of the work from a relatively large distance. If it turns out that
the contractor is not able to deliver the agreed quality, this monitoring can be
converted into supervision, whereby it is checked much more explicitly
whether the contractor is carrying out its work properly. If the contractor's
quality system works well, it is possible to supervise the work less intensively.
Assessment plan
The client uses an assessment plan to answer the question as to whether
the contractor's quality plan functions as it should. This includes three
types of assessments: system assessment, process assessment and prod-
uct assessment.
These assessments must make clear whether the contractor carries out
all the quality assurance measures in accordance with its quality plan, whether
the checks carried out by the quality assurance personnel also actually
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