In the beginning
Boskalis’ strength is its ability to undertake projects in a variety
of circumstances and in diverse locations. To meet the high
quality of service expected by its clients, Boskalis organises itself
by sourcing logistics support, entering into subcontracts with
suppliers and setting up offices.
Once offices were established in Darwin and sufficient
accommodation was secured, Boskalis entered into an agreement
with local suppliers and major local subcontractors for, amongst
other things, the procurement of approximately 750 000 t of rock.
Local vessels were obtained to support the dredging campaigns
and to bring onboard resources to carry out the shore approach
works, including the procurement of a 600 t linear to perform the
pipe-pull.
Rocking in the top end
The quarries being utilised to source the required 250 000 t of
filter and 500 000 t of armour rock are located approximately
100 km from Darwin. The rock is quarried and transported in quad
road trains to the intermediate stockpile areas located close to
Darwin’s East Arm Port, where the rock load out facility will be
located.
HBOJV is the Darwin based joint venture contracted by
Boskalis to produce and transport the rock. Boskalis recently
congratulated the HBOJV transport team for reaching a
1 million km incident and injury free milestone. Using local drivers
with good knowledge of Darwin and surrounding areas, the team
has safely and successfully transported 500 000 t of rock from
Mount Bundey quarries to the intermediate stockpile areas since
June 2013.
Trench dredging
The trench was required to be dredged over a length of
approximately 16 km, in varying soil conditions and at various
depths, leading Boskalis to deploy a number of different dredgers.
Dredging was initially executed with the trailing suction
hopper dredger (TSHD)
Queen of the Netherlands
, which
removed the soft overlying material. The remaining offshore
trench profile dredging was undertaken utilising the backhoe
dredger (BHD)
Baldur
and the backacter (BA)
Simson
, supported
by self-propelled split hopper barges and shallow drafted non-
propelled split hopper barges for the shallower sections of the
trench.
Offshore, pre-sweeping 60 km from Darwin Harbour was
undertaken utilising the TSHD
Queen of the Netherlands
and some
nearer shore pre-sweeping was undertaken with the BA
Simson
and the BHD
Baldur
.
Near shore, the BHD
Baldur
carried out bedding layer dredging,
following which a filter bedding layer was placed.
Shore approach
Prior to the pipelay commencing, a shore approach needed to
be constructed in difficult and varying soil conditions. Initially, it
had been the intention to construct an open trench through the
entire shore approach, but this was not possible and a cofferdam
was required through the most challenging soil conditions in the
mangrove swamp area. An open trench was constructed through
the salt flat, but the soil conditions in this area also proved to be
extremely soft and various work methods were required before
the trench was completed.
Pulling the pipe
A 600 t linear winch was mobilised and installed at the beginning
of the trench at the shore approach. Together with 3300 m of
121 mm dia. wire, the winch was used to pull the pipe from the
pipelay vessel
Semac 1
onto the shore. Buoyancy tanks were
installed on the pull wires and a number of pipe rollers were
installed in the trench to assist with the pull.
Figure 2.
Backacter
Simson
.
Figure 4.
Rock delivery.
Figure 3.
Backhoe dredger
Baldur
dredging the shore
approach.
74
World Pipelines
/
SEPTEMBER 2014
