Optimizing Soft Ground Excavation: Development and Design of EPB and Slurry Cutterheads
The history and development of soft ground tunnelling machines is a long one, and one in which the quest for optimal design to achieve safe and efficient excavation has always been a top priority. Modern soft ground tunnelling began with the introduction of Slurry TBM technology in 1967 and the development of Earth Pressure Balance (EPB) machines a bit later in 1974 in Japan. Many advances have since been made by Japanese manufacturers, as well as North American and European manufacturers. These advances were the result of lessons learned from the successes and failures of the technologies in a variety of geologies. In many cases the philosophies of Japanese and European manufacturers were quite different, resulting in unique machine features. In the case of both EPB and Slurry, many of these advances have involved the development of the cutterhead, which is the first part of the machine to come in contact with the soil. Cutterhead design is not only integral to operation of the TBM, but also to machine performance. Proper cutterhead design must incorporate a variety of project variables including expected geology and operation of the machine. To appropriately specify and evaluate soft ground cutterhead features, there must be an appreciation of how these features developed and how this applies to a job-specific geology.
This paper will review the fundamentals of cutterhead design and how particular attributes interact with the geology and other machine features to achieve efficient excavation. When possible, comparisons between EPB and Slurry technology will be addressed. Comparisons will also be made between the varying schools of thought in terms of soft ground machine design in both Europe and Japan. In addition, the features will be evaluated for potential outcomes with differing geologies and methods of operation. A thorough understanding of these items allows for an educated approach to maximization of machine advance and performance.
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