Hybrid immersed tunnel element
Immersed tunneling is a method of constructing relatively shallow undersea tunnels. For ease of construction and economic efficiency, immersed tunnels are divided into several elements (immersed tunnels), which are fabricated at docks and other fabrication yards. The structure of the immersed tunnels is generally a composite structure consisting of steel shells and concrete, and can be either full-sandwich or semi-sandwich (open-sandwich).
Construction method features
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High rigidity and high load-bearing capacity
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Steel shell is a floating structure and concrete can be cast at sea.
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Reduction in the amount of reinforcement, formwork and support works.
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Rapid on-site construction
Hybrid immersed tunnel element (Overview of construction method)
1.Overview
Hybrid immersed tunnel elements are adopted for navigation channels and canal crossings in port areas.
(Compared to immersed tunnels, bridge and shield tunneling methods have longer approaches and higher total costs.)
Full-sandwich types
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No reinforcing steel is used.
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Filled with high flow concrete
Semi-sandwich (open-sandwich) type
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Partially reinforced with steel reinforcement.
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Placing ordinary concrete.
Construction examples
| Name of construction work | Sumida River (downstream of Azuma Bridge) right bank terrace construction (No. 2-2) |
|---|---|
| Client | Tokyo Metropolitan Government |
| Purpose/function | Water-friendly revetment |
| Year of construction | 2012 |
| Dimensions | 62.0 m (length) x 3.75 m (width) x 4.2 m (height) |
| Number of units manufactured | 1 unit |
| Weight | ー |
| Steel weight | 265 t |
| Concrete volume | ー |
| Design overview | Installation depth - 2.35 m |
| Features/functions | Steel pipe pile foundation |
| Name of construction work | Shinwakato Road immersed tunnel (element No. 3) construction manufacturing work |
|---|---|
| Client | Ministry of Land, Infrastructure, Transport and Tourism Kyushu Regional Development Bureau |
| Purpose/function | Immersed steel shell |
| Year of construction | 2007 |
| Dimensions | 81 m (length) × 28 m (width) × 8.4 m (height) |
| Quantity (/case) | Body weight: 1940 tons |
| Features/functions | Steel-concrete full sandwich structure Floating towing |
| Name of construction work | Osaka Port Yumeshima Tunnel immersed steel shell (element No. 1) manufacturing work |
|---|---|
| Client | Ministry of Land, Infrastructure, Transport and Tourism Kinki Regional Development Bureau |
| Purpose/function | Immersed steel shell |
| Year of construction | 2004 |
| Dimensions | 97 m (length) × 36 m (width) × 9.4 m (height) |
| Quantity (/case) | Weight of steel: 3360 tons |
| Features/functions | Steel-concrete full sandwich structure |
| Name of construction work | Naha Airport (Naha Wharf Zone) road (airport line) immersed steel shell (element No. 3) manufacturing work |
|---|---|
| Client | Naha Harbor and Airport Construction Office, Okinawa General Bureau, Cabinet Office |
| Purpose/function | Immersed road |
| Year of construction | 2003 |
| Dimensions | Height = 8.7 m, width = 36.94 m, length = 90.0 m |
| Quantity (/case) | Dead weight = 2910 tons |
| Design overview | Installation water depth = -24.0 m |
| Features/functions | Full sandwich structure, high-fluidity concrete |
| Remarks | 6-lane road (3 lanes on each side) Concrete applied to floating steel shell |