HSE Annual Report 2010 (English) - WINTERSHALL

GERMANY: MICROTUNNEL – WORKING IN COM-
PRESSED AIR CONDITIONS.
The Baltic Sea Pipeline Link (OPAL) will pass below
the River Peene via a microtunnel that was drilled
in a depth of up to 25 meters. This method was
chosen to protect the sensitive countryside and
surrounding nature reserve. A tunneling machine
with a diameter of three meters was used to drill a
tunnel from the entry pit to the exit pit 1,000 meters
away. As the machine advanced, 4-meter concrete
segments were inserted in the tunnel. At the completion
of the tunnel, the pipes for OPAL, which had been
welded together beforehand, were drawn in.
The discovery of a granite erratic boulder of around
three meters in diameter after 650 meters of drilling
resulted in the cutting tools having to be replaced
on the drill head at a depth of around 22 meters.
The position below groundwater level was a
challenge. Due to the prevailing conditions in the
subsoil, the tool had to be replaced with the front
section of the tunnel pressurized using compressed
air. This ensured stability, enabled access and prevented
an excessive influx of groundwater. Extensive
sealing work for the tunnel and surface were
necessary to make the working area air-tight. The
pressure at the drill head was 2.3 bars, equivalent
to that when diving at a depth of 20 meters. Consequently,
special compressed air equipment was
needed to ensure safe working conditions and
minimize the physical strain and stress. The technicians
worked in three shifts, each lasting 2.5
hours; it also took around 3 hours to prepare the
workers for the face and another 3 hours to return
them to the surface in a compression chamber.
The entire work program was supervised by an
occupational physician and coordinated by a team
of professional divers.
HEALTH SAFETY ENVIRONMENT 2010