Exploring Submerged Floating Tunnels: How They Work, Unique Features, and the Challenges They Pose

Tunnels under water have been a thing in civil engineering since the 1900s. Bridges and tunnels are the usual go-to for crossing water bodies, but when the bed is rocky, deep, or undulating, the Submerged Floating Tunnel (SFT), also known as Archimedes bridge or suspended tunnel, steps in.

Navigating the Depth Dilemma: Why Choose a Floating Tunnel?

Imagine a waterbed varying in depth from place to place – some spots as deep as 8 km! Traditional options like a bridge or a tunnel beneath the ground face challenges here. Constructing a bridge with columns reaching that height? Impossible. Plus, the pressure below 8 km is intense – 500 times atmospheric! That’s like trying to survive in a high-pressure zone. So, the sweet spot for a floating tunnel is 30 m below sea level, where the pressure is manageable, letting even big ships pass by freely.

Diving into the Basic Principles of Submerged Floating Tunnels

Picture the SFT as a buoyant structure gently moving in the water. The relationship between buoyancy and self-weight is crucial, controlling how the tunnel behaves. There are two ways to make an SFT float:

1. Positive Buoyancy: Anchor it with tension legs or pontoons, keeping it around 30 m below the water surface.
2. Negative Buoyancy: Use piers or columns to connect to the sea or lake bed, suitable for up to 100 meters of water depth.

But, like a ship in a storm, the SFT faces environmental challenges: currents, waves, corrosion, earthquakes, ice, and marine growth. It needs to be designed to withstand it all!

Unveiling the Features of Submerged Floating Tunnels

1. Clear Sight: Crossing waterways can spark debates, but SFTs may preserve beautiful or historically significant areas without disrupting nature.
2. Fixed Length: The SFT’s length equals the distance between two shores, and it can connect directly to other tunnels.
3. Very Low Gradient: Unlike bridges or undersea tunnels with higher costs, SFTs offer a gentle gradient, saving energy for traffic.
4. Access to Underground Spaces: Imagine having underground service areas or parking directly accessible by lifts into towns or cities.
5. Surface Proximity: SFTs can surface close to the shoreline, facilitating flexible links to road systems.
6. Constructed Away from Crowded Areas: For cities clogged with traffic, SFTs offer a solution. Constructed away from busy spots, they’re towed to the site for installation, minimizing disruptions.

Considering the End Game: Removal and Recycling of SFTs

All structures have a lifespan, and planning for removal is crucial. SFTs, being floating structures, can be towed away for reuse or recycling. Sections could find new life as storage facilities or other purposes.

Facing the Hurdles: Challenges in Adopting Submerged Floating Tunnels

1. Cost Challenges: With a plethora of materials and machinery involved, the estimated cost of SFTs is nearly double that of a regular tunnel.
2. Fire Hazards: Rescuing people in case of a fire within the tunnel becomes challenging.
3. Collision Concerns: If two trains or vehicles collide, rescuing passengers isn’t straightforward.
4. Discomfort for Train Passengers: Passing through a tunnel generates pressure waves that may cause discomfort for passengers unless the trains are pressure-sealed.

In conclusion, the Submerged Floating Tunnel concept brings innovation to the table, offering unique solutions and posing challenges that engineers are diligently working to overcome.