Expanding Maritime Infrastructure: The Role and Construction of Caissons

In many urban centers worldwide, the demand for land and space is rapidly outpacing supply. This trend is especially evident in maritime hubs, where the relentless expansion of commercial maritime traffic and activities driven by the surge in international trading has created a heightened need for efficient port and harbor utilization. Consequently, construction efforts are predominantly focused on expanding existing facilities to meet these growing demands.

Importance of Port and Harbor Infrastructure

Port and harbor infrastructures are vital for:

• Enabling marine traffic
• Facilitating vessel construction and repairs
• Providing protection against wave action
• Supporting loading and unloading operations

These functions are crucial for fostering international commerce. To support these activities, various marine works and harbor constructions often require the use of caissons.

Applications of Caissons in Maritime Construction

Caissons are used in the construction of:

• Ports
• Breakwaters
• Wharves
• Berthing facilities and docks
• Dry docks and slipways
• Fishing ports and marinas

Floating Caissons Fabrication Process

1. Initial Construction:

• Slab Formation: The fabrication of each caisson begins with the slab. The slab reinforcement cage is assembled on an auxiliary floating platform before being moved to the floating dock.
• Concrete Pouring: A sliding form is used to pour the slab as a monolithic element.

2. Building the Upper Structure:

• Incremental Construction: The upper part of the caisson is constructed in increments of one meter. This involves placing reinforcement, sliding the forms, and pouring and vibrating the concrete. This sequence is repeated until the caisson reaches its full height.

3. Releasing the Caisson:

• Preparation for Release: Once the caisson is completed, special supporting and locking bars are removed to allow the caisson to float.
• Guidance to Final Location: The floating caisson is guided to its final location with the help of cables and tow-boats.

4. Filling the Caisson:

• Filling Cavities: The caisson's cylinder cavities are filled with granular material. Auxiliary floating platforms carry the material and a crane to transfer it.
• Surface Work: Tractors, dozers, loaders, and trucks complete the filling operation on top of the caisson.

Construction of Hand-Dug Caissons

Hand-dug caissons, a traditional piling method, are almost banned in some regions due to safety concerns. The process involves:

1. Setting Out: Position and size the caisson.
2. Excavation: Excavate one meter into the ground and erect a caisson lining steel form.
3. Concrete Lining: Pour concrete for the caisson lining.
4. Platform Installation: Erect an excavation platform on top of the caisson center.
5. Repeat Process: Continue steps until reaching bedrock.
6. Bellout Excavation: Excavate bellout into bedrock.
7. Reinforcement: Fix caisson reinforcement.
8. Concreting: Install concreting chute and pour concrete to the required level.

Preventive Measures and Monitoring

Preventive Measures:

• Grouting: Stabilize unstable subsoil layers encountered during excavation to prevent excessive settlement of adjoining structures.

Monitoring:

• Settlement Monitoring: Regularly monitor checkpoints to ensure building and pavement settlement does not exceed specified limits.
• Groundwater Monitoring: Install standpipes piezometers to monitor groundwater table drawdown.
• Reporting: Submit monitoring results to consultants regularly and keep records available for inspection.

Caisson Sinking Methods

There are two primary methods for lining a well with caissons:

1. Unlined Digging and Lowering: This method involves digging an unlined well and then lowering the caissons into place, similar to the in-situ lining method but without the benefits of a tight grout seal.
2. Pre-Cast Sections: Another method involves digging a starter hole or placing the bottom caisson directly on the ground. Pre-cast sections are secured together to ensure stability during construction.

Finishing the Well:

• Gravel Base: Fill the bottom with gravel to ensure good water flow and prevent fine materials from moving up.
• Perforations: The bottom sections may be perforated to increase inflow, although this can reduce structural strength.

Conclusion

The construction of caissons is a critical component of expanding maritime infrastructure, enabling ports and harbors to meet the growing demands of international commerce. Understanding the detailed process of caisson fabrication and installation helps ensure safe and efficient construction practices, ultimately contributing to the effective utilization of maritime facilities.