mohring engels.indd - Keramo Steinzeug

Fig. 18: Starting shaft
(3.20 metres) with shield jacking
of DN 500 vitrified-clay pipes
For nominal sizes greater than DN 800 rectangular shafts
must generally be dug. Alternatives for all nominal sizes
are starting shafts of reinforced shotcrete, which lend
themselves well to confined spaces, or the ONE-PASS
SHAFT LININGS from England. The latter are prefabricated
concrete tubbings which can be assembled on
site, are available in a variety of bores from 1.52 to 10.67
metres and are reusable.
The shafts needed for thrust boring road sewers are also
the starting point for thrust boring house connections,
which are thrust bored to the plots in a radial way. If the
shafts are arranged carefully according to local conditions,
several plots can be reached from one shaft without
any overlength arising for the particular house connection
or need to tunnel under other plots.
In the Berlin method type I the plots which cannot be
reached from the starting or target shafts are
accessed – also radially – from sunk ”by-shafts”. In the
by-shaft the feeder-sewers are linked to the collector by
backdrops and fittings. If the collector is above the
groundwater, the by-shaft is sunk using liner-plate rings
after thrust boring of the collector has been completed
and retracted for re-use when the house connections
have been constructed (Fig. 19). If the collector is in the
groundwater, prefabricated reinforced-steel shafts are
used for the by-shafts and sunk before any thrust boring
starts. Like the starting and target shafts, they are
sealed watertight under pressure under the sewer bottom
with an concrete seal preventing buoyancy.
Micro-tunnelling Page 17
Pipe jacking then takes place through prepared apertures
with collar seals against the pressing groundwater
from the starting to the target shaft, through the byshafts
which remain in the soil (Fig. 20). In the final cycle
the starting and target shafts are finished as manholes
with the usual dimensions.
In the Berlin method type II the ”by-shafts” are replaced
by additional starting, target or intermediate shafts
linked radially to the house connections; when construction
is completed, these become ordinary manholes into
the sewer system (Fig. 17). This version meets the requirement
in ATV A 142 that in Protected Zone II waterprocurement
areas all feeder-sewers must be -connected
to access-hole structures.
The usual alternatives for finishing/converting the
starting, target and intermediate shafts as/to ordinary
manholes into the sewers are evident from Fig. 17 in
conjunction with the diagrams in Fig. 21 to 23.
Fig. 19: Berlin method: by-shaft above groundwater table