The Constructor

Floating Caissons

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In certain cities and even countries the demand for land and space is rapidly exceeding the supply. Maritime centers do not escape from this reality, the continuous expansion of commercial maritime traffic and activities in seaports due to increases in international trading has generated an increased demand for an effective use of ports and harbors. Construction activities have been oriented to the expansion of existing facilities

Port and harbor facilities form the infrastructure that makes marine traffic possible, facilitating the construction of vessels, its protection against wave action and its loading and unloading activities. In other words, they play an important role in facilitating international commerce

The different marine works and harbor constructions in which these caissons can be used include:

Floating Caissons Fabrication

Each caisson is built in an ascending sequence starting with the slab. The slab reinforcement cage is assembled in an auxiliary floating platform, then the cage is moved to the floating dock. A sliding form is placed and the slab is poured as a monolithic element.

After the slab is ready, the construction of the upper part of the caissons begins, ascending in increments of one meter using the sliding form Each of these increments includes: placing the reinforcement, sliding the forms, and pouring and vibrating the concrete. This sequence is repeated until the total height of the caisson is reached.

Once the caisson fabrication is completed, a special set of supporting and locking bars are removed to allow the release of the caisson from the floating dock. The caisson floats by itself and is guided with the help of cables from the shore and tow-boats, to its final location. When the caisson reaches the final position the cylinder cavities begin to be filled with granular material.

This operation is performed by auxiliary floating platforms that carry both the material and a special crane to transfer the material. Tractors, dozers, loaders and trucks help finish the filling operation on top of the caisson In the floating dock, operations begin for the fabrication of the next caisson

Step 1 - Construction of Hand-dug Caisson

Installation of Hand-dug Caisson

Step 2 - Preventive Measures

Step 3 - Monitoring

Caisson Sinking

There are two methods for lining a well with caissons. The first method involves digging an unlined well and then lowering the caissons into place. This is very similar to the in-situ method of lining.

It has all the same problems of safety but without of the benefits of a tight grout seal along the edge of the well. Problems also arise if the hole is not straight and uniform. The additional backfilling that is required also makes the method undesirable.

Digging a Caisson Lined Well

A starter hole can be dug first, or the bottom caisson can be placed directly on the ground. It is important to make sure the first few segments start out strait and level. As the hole progresses the upper sections will keep the lining strait, but it must be straight to begin with.

If separate pre-cast sections are used it is important that the sections are secured together. If the sections are simply stacked, the bottom caisson, or the cutting ring, can fall out of place while the stack progresses. This is potentially dangerous and it can be impossible to recover from.

Finishing a Caisson Lined Well

When the bottom of the caisson reaches the required depth, the bottom should be filled with 7-10 cm of gravel to allow good flow up to the well but prevent fines from moving up. To increase the inflow, the bottom sections are often perforated.

Some sources recommend always using a perforated or porous material on the sections under the water table. Others say that joints between the sections will allow substantial flow and modifying the bottom sections with holes or porous concrete is not worth the decrease in strenght

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