From easing congestion to carrying utilities, underwater tunnels create connections once thought impossible. But building beneath rivers, harbors or open ocean demands advanced technology, expert planning and flawless execution.
At Northern Construction, we specialize in navigating the complexities of large-scale tunnel projects—delivering durability, safety and long-term performance. In this guide, we’ll walk through the key stages of underwater tunnel construction and the innovations that make it possible.
The Purpose of Underwater Tunnels
Underwater tunnels are built to connect key points where over-water bridges aren’t sensible—whether due to active shipping lanes, environmental restrictions or visual impact. Depending on water depth, soil conditions and project demands, engineers select from three primary construction methods (explored in detail later in this article):
- Cut-and-cover tunnels: Made by excavating a trench, building the tunnel within it and then covering it back up.
- Bored tunnels: Created with a tunnel boring machine (TBM) that carves a path underground while installing tunnel segments.
- Immersed tube tunnels: Prefabricated sections are floated into place, submerged, aligned and sealed underwater.
These tunnels support a wide range of infrastructure, including:
- Road and rail transportation
- Water and sewer systems
- Electrical and fiber optic networks
Underwater Tunnels vs. Bridges: Which Is Better?
Both tunnels and bridges serve vital needs, but each comes with different impacts:
| Underwater Tunnel | Bridges | |
| Visual Impact | Minimal—little to no view obstruction | Highly visible structures |
| Weather Exposure | Protected from wind, ice, and snow | Exposed to the elements |
| Construction Complexity | High, especially under deep water | Generally easier for shallow spans |
| Cost | Typically more expensive | Often more cost-effective |
| Navigation Clearance | Unobstructed for ships | May require drawbridge or other clearance measures |
If you have questions or concerns about project needs, contact us today to partner with the leader in heavy civil construction.
The Biggest Challenges in Underwater Tunnel Construction
Tunnel construction is never simple, but building underwater adds entirely new layers of complexity:
- Water pressure: Structures must resist constant, intense external force.
- Sealing and waterproofing: Even minor leaks can compromise long-term safety and integrity.
- Soil conditions: Soft or uneven seabeds require precise engineering and stabilization.
- Worker safety: Confined, pressurized environments demand rigorous safety protocols.
- Weather and tides: Variable coastal conditions can disrupt timelines and impact stability.
Successfully overcoming these hurdles takes experienced crews, advanced monitoring systems and real-time problem-solving—all of which Northern Construction delivers.
How Are Underwater Tunnels Built?
Building a tunnel under a body of water demands precision planning, high-performance equipment and expert coordination. Here’s how it’s done, step by step.
1. Site Investigation and Planning
A successful tunnel project begins with a thorough understanding of the ground and water where it’s being built.
- Geotechnical surveys assess the composition of the soil and rock.
- Hydrographic studies map underwater conditions and currents.
- Environmental assessments evaluate potential impacts on aquatic ecosystems and nearby communities.
These findings guide key decisions, from selecting the most suitable construction method to determining the optimal tunnel alignment.
2. Tunnel Design and Engineering
Every tunnel is unique, so design teams consider several factors, including:
- Tunnel length and depth
- Traffic volume and utility requirements
- Soil type and water pressure
- Nearby infrastructure
Advanced tools such as 3D modeling and simulation software—along with collaborative planning—guide the design process from every angle.
3. Construction Methods
Cut-and-Cover Tunnels
Cut-and-cover tunnels are ideal for shallow underwater areas—such as those beneath rivers or harbors—with soft, navigable bottoms. The construction process typically includes:
- Dredging a trench in the waterbed.
- Installing temporary retaining walls or cofferdams to hold back water and create a dry work area.
- Building tunnel sections in place or lowering prefabricated segments into the trench.
- Sealing the joints to ensure water-tightness.
- Covering the structure with backfill material.
Bored Tunnels
Bored tunnels are ideal for deep, long-distance projects beneath rivers or coastal zones—especially in or near urban areas. These tunnels are constructed using a Tunnel Boring Machine (TBM), which:
- Cuts through soil and rock with precision.
- Installs pre-cast tunnel segments directly behind the cutter head.
- Maintains a dry and stable environment within the tunnel as it progresses.
- Continuously advances forward, minimizing surface disruption.
Immersed Tube Tunnels
Immersed tube tunnels are often used in wide bodies of water where boring isn’t practical, combining the speed of prefabrication with the durability of in-situ placement. The process typically involves:
- Prefabricating tunnel segments on land.
- Sealing each segment to ensure it’s watertight.
- Floating the segments out to the site and aligning them in position.
- Preparing the trench on the seabed for segment placement.
- Submerging and positioning the segments one at a time in the trench.
- Connecting and sealing the segments to form a continuous tunnel.
- Covering the structure with protective material to safeguard against external elements.
When you partner with a 1:1 expert, the best method for your project will balance feasibility with long-term function, ensuring all essential infrastructure needs are met.
Navigate and Achieve Your Project Goals With Northern Construction
Construction in the Northeast requires the utmost expertise due to our environmental, permitting and geological circumstances. At Northern Construction, we bring decades of experience to complex projects both above and below water. Whether you’re building a new crossing or upgrading existing infrastructure, we deliver tailored, safe and durable solutions that always perform. Contact Northern Construction to learn more about how we support underwater tunnel construction and many other construction needs with the fullest expertise available.