Marine Structures are becoming bigger and bigger
To carter to big marine constructions, the precast structures such as caissons, culverts, are becoming bigger and bigger in both weights and size. From 1990 years, the unit weight of concrete caissons for gravity wharf construction reach 1000 tonnes.
Demands for transport heavy structures are increasing
To handle with concrete structures below 500 tonnes, the traditional way is using gantry crane and crane barge. For 1000 tonnes or heavier ones, using bigger crane is not a economical way, the associated equipment and infrastructure cost increase much
New solutions for heavy moving
Comparison of traditional heavy structure moving methods
- Gantry Crane hoisting plus crane barge
Using crane to hoist and move concrete structures faced the bottleneck when structure weights reach 1000 T.
- Trolley moving plus submersible barge
Moving caisson with Trolleys from land to submersible barge is a mature technology, can deal with thousands tonnes concrete structures. But the investment of trolley and infrastructure is costly
- Skateboard hauling method
By deploying skateboard to increase the contact area of being moved structure with ground and also a pulling force to move structure forward. This method is suitable for small size and light structure moving only because the pulling force required to move structure must be bigger than the friction force which will be quite big once structure weight increases.
- Water cushion
Pump water into a dish form rubber container and press water spray from container hem, thus the rubber container will have ability to lift weight.. The water membrane between caisson with ground make the friction coefficient comes to be very small, so to move structure is easy.
This method has some limits: needs very good ground condition and being difficult to move structure continuously.
- Airbag Heavy Moving
Inspired by ship launching with airbags, civil engineers tried four units airbags to lift one 500 T caisson 40 cm high then moved it forward 10 m far in Fujian Province in 1997 years.
In 2000 years, the airbag heavy moving technique combined with submersible barge transport, completed 7 units 800 T caisson land and water transport in Shuidong port. Nowadays 5000 T caissons have been successfully moved onto floating docks or submersible barges with airbags.
Advantages:
No Crane needed onshore or offshore
Marine airbags are made or rubber, they act like rubber cushion which can protect the moved structure.
Using airbags to move concrete structure has low demands of moving pass, compacted natural ground is acceptable.
Being flexible. One size of airbag can be used for different structures moving by staggering airbags.
Being economical. Airbags can be used for more than 6 years and they can be repaired even get damage.
Disadvantages:
Low speed. Using pneumatic rollers to move structure the speed is about 1-2 m per minute.
More hands. Lots of airbag operations needs to do by hands.
Needs experienced engineers and manpower.
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