mohring engels.indd - Keramo Steinzeug

Fig. 9: Pilot pipe jacking
system work below the water table is now also possible.
The thrust boring of DN 200 sewers in section lengths
which is now feasible is acquiring pre-eminent importance.
The accurate underground driving of sewers of
this nominal size at the customary section lengths was
not possible earlier with the thrust-boring systems
available on the market. From the inception of microtunnelling
the conveying equipment to be incorporated
inside the jacking pipe for moving the displaced soil, including
protective tubing for cables, and the essential
optical channel for the laser beam to control the advance
determined nominal size DN 250 as the smallest crosssection
of access-hole length drivable underground. For
operators this meant that for constructing collectors
they had to dispense with the customary smallest nominal
size DN 200 if on economic grounds or because of
compelling local factors enclosed construction methods
had to be preferred to conventional sewer construction.
Fig. 10: Pilot pipe jacking, final
phase: after-pushing of the vitrified-clay
pipe from a DN 2000
starting shaft
How widespread DN 200 is in the public sewage systems
is shown by figures from the BWB’s combined and
domestic/industrial sewage systems: some 32% of the
BWB’s 8613-km long sewage system is of this nominal
size. Particularly in the separate systems’ domestic/industrial
sewage networks large parts of the drainage areas
can be developed with DN 200 circular cross-sections
and are hydraulically fully adequate for all operational
requirements. If one considers the Berlin domestic/industrial
sewage networks alone, DN 200’s share is
as much as 65%. Because of this special importance
operators have never abandoned the desire and requirement
to be able one day, with improved technology, for
controlled driving of DN 200 pipes too. This has now
been made possible by the work of three German machinery
producers in particular and provides planners
and operators with other alternatives and the means of
investing more economically since sewer construction is
becoming more cost-effective.
The requirements of ATV A 125, Section 6.2.2 governing
the measuring and logging of runs of piping in the construction
of jacking systems are met. During the jacking
process, for example, the image on the monitor in the
starting shaft can be continuously recorded by a videorecorder.
All possible deviations are thus registered.
Moreover, when product pipes are installed, the jacking
pressure can be recorded by a pressure transducer with
a memory by a recording manometer of the peak value
in the measurement period.
Thrust-bore pipe jacking
Micro-tunnelling Page 11
Here the product pipes are advanced at the same time
as soil is displaced at the face by a cutting head. The
soil is continuously conveyed to the starting shaft by
augers. The augers are in a steel tube inside the jacking
pipe. With each installed pipe the auger and pipe string
is lengthened. The conveying pipes have skids and, like
the augers, are adapted to the bore of the particular pipe
to be jacked.
In the starting shaft the soil is collected in a steel bucket
during a jacking period and conveyed to the surface
during the coupling operation. In this way the quantity
of soil actually removed at the face is reliably monitored.
An alternative to bucket extraction is to set up a sump in
the starting shaft and convey by pumping. Fig. 11
shows a thrust-boring container with a Soltau thrustbore
pipe jacking system.
Cutting head and augers are normally driven from the
starting shaft. For heavy soils it is necessary to have
available consistently high torque to comminute the
drilled matter effectively. From DN 400 upwards pipejacking
machines are therefore also offered with directly
driven cutting head and separately driven augers.