After thorough engineering and analysis, it was
concluded that the soil conditions and geological
features were too challenging for conventionally drilled
crossings. Therefore, a concrete tunnel had to be made
to accommodate these two pipelines. Furthermore, in
anticipation of an increasing draft of the container vessels
sailing to Hamburg, the tunnel had to be laid at a significant
depth under the surface. With these challenges ahead,
A.Hak Drillcon took on this task.
Initially the contract was awarded to a consortium of
contractors, each contributing its specific expertise. However,
after a forced restructuring of the consortium, the entire
contract was diverted to A.Hak Drillcon.
On 4 December 2014, A.Hak Drillcon’s AVN 2400 tunnel
boring making (TBM) concluded the subsurface drilling, when
it emerged in the reception shaft on Lühesand Island near the
South bank of River Elbe.
In an impressive timespan of less than 4 months, the access
to the Port of Hamburg was traversed with a 3 m dia. concrete
casing at a depth of 33 m under the surface.
Even before the project started, all parties involved were
aware of the huge technical challenges associated with the
construction. The diversified ground ranged from sandy gravel
soil with stones through layers of boulder clay featuring larger
rocks to layers of clay, which tends to be very sticky. This was
exacerbated by high water pressures of up to 4 bar.
Challenging soil conditions
Most challenging for the tunnelling works were the varying soil
conditions along the route, with the cutting head negotiating
itself through clay, marl, cobbles, boulders and sand as it
propelled its way forward. The tunnelling profile was designed
to consistently drill into the most adequate layers, which
resulted in a number of level and angle adjustments along the
track. Despite these alternating levels and angles, a profoundly
analysed buoyancy and bentonite lubrication system kept the
pushing forces well within the predetermined limits.
The machine also encountered large boulders when it had
reached almost 200 m into the route. But as such geological
conditions had in fact been anticipated, the jobsite team
swiftly overcame these obstacles thanks to their experience
and thorough preparations.
Steering, surveying and monitoring
Thanks to laser navigation technology supplied by
Herrenknecht’s subsidiary VMT, the jobsite crew managed
to steer the AVND-2400 right along the specified route and
precisely into the target shaft.
The navigation of the TBM was controlled by means of
VMT’s SLS Microtunnelling LT system. This system is based
on the technology of a ride-on laser, which is a proven and
continuously perfected VMT navigation technology.
The TBM’s programmable logic controller (PLC) was
continuously connected to the control systems on the surface,
facilitating an uninterrupted data collection of all available
machine data.
In order to use this large inflow of data effectively and
evaluate it, the web-based data management system IRIS
Microtunnel fitted excellently. This system has been developed
in co-operation between VMT and the ITC Engineering GmbH
& Co KG, and proved very valuable and useful.
In this system the accumulating data can be recorded
and processed in various fields. This project is specifically for
engineering and navigation data, as well as the connection
to a GeoScanner (acoustic measurement system for the
determination of particle sizes and distribution of the
transported material on the conveyor line) as well as the
realisation of an automatic alarming when limits are exceeded.
Project-specific machine modification for 4 bar
water pressure
Before the machine was mobilised and launched, special
inspections and modifications had to be done. The main
bearing of the cutting head was inspected by videoscope
analysis, and found to be in order to complete the drilling
without further maintenance.
Then the machine had to be adapted to withstand the
water pressure of approximately 4 bar due to the depth under
the water surface. The main bearing sealing was modified,
and the entrance door to access the cutting head had to be
modified to withstand this pressure. All was done thoroughly
and no problems of any kind have arisen during the tunnelling
operations.
Miner’s patron Saint Barbara celebration
On 22 October 2014, peak ‘depth’ was reached at half the
distance. This milestone occasion after an impressive tunnelling
speed was marked in the miner’s tradition by having the miner’s
patron Saint Barbara celebration on the jobsite.
Bentonite
During the project, professional consultancy was obtained
from the supplier of the bentonite for the most optimal
drilling fluids in the various phases of the project, based on
the available soil investigations. Stability tests were carried out
with the soil samples, at the drilling location.
For the front of the tunnel machine, Cebogel OCMA
was used because of its good carrying capacity, high gel
strength and an excellent filtercake capability. Since drilling
had to be done through different soil layers, of which some
of them had cracks, this product was considered most
suitable. Furthermore, Cebogel OCMA is also easy to use in
Figure 2.
Immobilisation of the shield on Lühesand Island.
150
World Pipelines
/
AUGUST 2015
