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ately, and the depreciation figures are lowered. This in
turn means lower sewerage charges. Further information
on this, with examples, may be found in the article
by Thymian, Möhring and Friede ”The economic significance
of quality assurance in sewer construction”
(STEINZEUG Information 1996).
Micro-tunnelling Page 31
9. Recommendations for carrying out
micro-tunnelling
In the public mind micro-tunnelling does not enjoy anything
like the importance due to it by virtue of its technical
and economic scope. Why is this? The main causes
are
– deficient awareness of the stage reached by developments.
For operators there is in many cases still
something exotic about enclosed sewer-construction
methods, which are decided on only when conventional
solutions appear inadvisable;
– uncertainties in planning, tender-specification and
preparatory matters;
– distrust, especially re: success in difficult subsoil conditions;
– hesitation by companies because the frequency of
use once capital has been invested cannot be
gauged.
In a modern technical development such as micro-tunnelling
there will be constantly new challenges for all
concerned. Any client and any planning consultant engineer
can however trigger impulses in order to increase
the cost-effectiveness of micro-tunnelling in his sphere
and have a hand in determining success in the market.
For this the following suggestions may be helpful:
1. In each sewer-construction project cost-effectiveness
comparisons should be drawn up for the open
and enclosed methods. In these, all factors affecting
the open methods in particular should be taken objectively
into account such as previous re-routing of
pipes, traffic lights and necessary digging up and
restoring of the road, soil replacement, dewatering
and the duration of construction work.
2. Where a cost-effectiveness comparison shows
approximate equality, the market should be challenged
with alternative specifications.
3. Micro-tunnelling is unsuitable for short underground
crossings of embankments, railtrack, waterways or
road intersections. The longer a construction site,
the more favourably do the relatively high cost
shares for investment in this technology pan out.
4. Frequent invitations to tender for micro-tunnelling
work are signals to contractors that investing in
modern technology might be worthwhile.
5. Standardisation of the major elements in pipe
jacking, starting, target, by-shafts and intermediate
shafts and – where necessary and feasible – their
subsequent incorporation in the sewage system as
inspection shafts are a contribution to rationalisation.