Documentação Técnica

Documentação Técnica
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sexta-feira, 12 de agosto de 2011

Dredging Equipment Selection

The selection of dredging equipment is usually determined by the requirements of the contractor and the site conditions. With this information a contractor will select one or more appropriate dredgers from his fleet or more appropriate dredgers from his fleet or a supplier of dredging equipment will be approached to offer the most effective tool for the project, both economically and technically.

Appropriate project appraisal is of great importance. Straight forward dredging operations, often appear simple at the outset, but may turn out to be very complex and demanding. Comprehensive site investigations and a proper project preparation are a necessity, even when the projects are small sized, as the scale of operation is not large enough to absorb too much setbacks.

When approaching the selection from the project side, a number of selection criteria must be set up to determine the best equipment for the project. These criteria will be composed of one or more boundary conditions from the following list.


Soil characteristics

Soil characteristics are dominant in the entire dredging process as soil removal forms the reason for dredging in the first place. Proper knowledge of the material to be handled through soil investigation is of vital importance for the operation. In each type of application the soil should be investigated.

The requirements of dredging work

The type of work will indicate requirements for selectivity and accuracy of processing which may be the case for dredge mining or sand and gravel operations. Separation techniques used are often based on a constant feed of relatively dry material, which may exceed 50 m, but some sand and gravel operations tend to go deeper. High accuracy will be required for some mining projects to separate overburden from valuable minerals, but especially for environmental dredging very accurate positioning of the excavation is of great importance, because it will reduce the amount of underlying clean material being mixed with the contaminated toplayer.

Logistics

Accessibility and space of area for equipment will impose requirements of mobility of the dredger, such as for small scale irrigation and drainage projects. The different transport options and transport distance of the dredged material should be considered in initial site planning. Hindrance of ship traffic can play an important role during construction and maintenance of harbours, rivers and other waterways.

Site conditions

Weather conditions and especially waves, current and tides, which are often found in beach nourishment or sand by-passing projects as well as in offshore trenching, may render the application of some types of dredges less advantageous. Local site conditions as initial waterdepth of obstacles may also cause problems.

Other

Other requirements may impose strict limitations on the dredging operation such as legal (noise) of environmental (pollution) considerations.

Many of the factors which determine the selection of dredging equipment can be analysed after a site investigation and should be used in a proper project evaluation.

Each project will impose its particular requirements on the dredging equipment, while the combination of factors as listed above determine the dredger requirements. In the selection process priority should be given to those factors which have the strongest effect on the dredging operation.

In the table various dredge applications have been summarised according to the two most important selection criteria: soil characteristics and dredging depth.


Fonte: Universidad de Buenos Aires, Facultad de Ingeniería, Departamento de Transporte, Escuela de Graduados en Ingeniería Portuaria. www.graduadosportuaria.com.ar

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