e-mosty September 2018 Vessels and Equipment Used for Bridge Construction | Page 53
SUBSTRUCTURES
The North and South anchorages are triangular shaped
gravity structures with cable anchorages and transition
piers. The South anchorage also has a side span pier on
the anchorage.
Before placing the tower caissons, the following activities
on the sea bed were completed at each tower location:
Dredging: 3 meters of sea bed surface material
was removed using a clampsell dregder.
Inclusion Piles: 195 two meter diameter hollow
inclusion piles with a length of 34.25 meters
were driven by underwater hydro hammer.
Gravel Setting: A layer of gravel was placed by a
tremie pipe and levelled using a special
underwater hydraulic levelling frame.
Caisson foundations for the towers were prefabricated in
a dry dock and a wet dock, and the circular steel shafts
that ultimately support the tower legs above, were
fabricated at a nearby shipyard. The following activities
were completed for each caisson:
Dry dock works: A temporary dry dock was made
before official commencement of works, and
concrete for the lower part of caisson (almost
3/4) was cast after official commencement.
Towing to wet dock: The caissons were then
towed from the dry dock to the wet dock via a
dredged channel.
Wet dock works: The remaining concrete was
cast on the floating caissons and two steel shafts
were erected on each caisson. The steel shafts
were fabricated at shipyard close to the site and
delivered to the wet dock by floating crane.
Caisson sinking: The caissons were filled with sea
water and sunk at each tower location within a
200mm tolerance in X and Y planes.
Plinth & Tie beam: The concrete plinths and tie
beams at the top of the steel shafts were cast,
incorporating the anchor frame for the steel
tower.
Figure 5: Diagram of South Anchorage Block
The tower foundations are concrete caissons placed at -
40 m below sea level on a granular material supported by
improved soil with steel inclusion piles.
Figure 6: Diagram of caisson
3/2018