Dewatering, waterproofing and drainage - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 241

eral and the tendency to sintering in particular. The causes of problems in the operational
phase have often been shown to derive from loss of information between the construction
phase and the operational phase. Therefore an information flow based on such processed
data is advisable. This enables the information from the construction phase to be used to
optimise the maintenance plan in the operational phase.
5.4.3.3 Other quality assurance measures during the construction phase
The contracting firm has - independent of the detailed design - the largest influence on the
correct mounting and installation of the groundwater drainage. The contractor orders and
checks the materials being installed and is directly involved in the process of constructing
a fault-free drainage system with personnel and construction process. Defects caused in
the construction phase and the quality of construction are often the main causes of dam-
age to drainage systems, the resulting long-term maintenance costs and the fact that such
defects can provoke sintering. Correct installation and a responsible contractor can even
reduce or remedy defects, which are due to incorrect design.
The possibilities for action during the construction phase are in many areas. It is essential
to use an appropriate process for the construction of the groundwater drainage, to display
the necessary care in the selection of materials and their installation, and constantly check
the quality of the completed system. It is also possible to undertake targeted measures on
site, like for example directed water diversion or additional dewatering to react to special
events or local conditions. The quality assurance aspects can be differentiated into
- optimisation of the construction process and
- supervision of construction.
The latter point applies to both internal supervision in the contracting firms by the respon-
sible site management and external supervision by the responsible supervisors on site.
According to the [Ri-BWD-TU], the following points are particularly important:
- Drain lasers should be used to check the direction and exact invert level of the drain
pipes and should therefore be available in sufficient quantities.
- The drainage should generally be constructed in runs. The repeating sequence of work
activities (manhole, run, manhole etc.) should be checked by the site supervision. The
works should proceed continuously and the construction of the following permanent
element (pavement at the sides and road construction in the invert) should if possible
follow directly.
- Laying against the invert gradient of the tunnel is - even if a possible process - to be
avoided. Otherwise, special measures have to be taken to react to any encrustation in
the drain run.
- Drainage runs that are under construction or already completed must be protected with
appropriate measures against external actions and damage. This can be ensured either
by the completion of the following, permanent element (pavement, invert construction)
or - in case construction progress stagnates due to other reasons - through appropriate
protection measures.
- After the final completion of the drainage, its correct construction must be documented
with an acceptance protocol and a camera survey.