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Clogging and flow assessment tests with cohesive soils from SingaporeUnderstanding the geological-geotechnical characteristics of the excavated soil are essential for soft ground excavation with EPB machines, and this characterisation should include the resulting mixture as well, called the muck, after the addition of soil conditioners (e.g. water, foam, polymers). The EPB shield relies on the properties of this muck to maintain face stability. Muck transportation and its disposal are also key elements of the mechanised tunnelling process. Therefore, the modifications of the natural excavated soil with additives shall attend to the requirements not only of the excavation process itself, but also allow effective transportation and disposal, including the specific limitations imposed by environmental aspects. In the case of cohesive soils, the characteristics of clogging potential and the flow behaviour play a key role during the entire tunnel operation. Clogging, meaning the soil sticking to the metal parts of the machine, can delay tunnel advance, even considerably increasing excavation costs. Correlations of the muck flow properties with mechanical parameters, such as the torque (cutterhead and screw conveyor) and pressure (excavation chamber and screw conveyor), as well as the material transportation through means of the conveyor belt or muck pumping system, are possible. This paper presents the results of laboratory tests conducted with cohesive soils from Singapore, correlating the results with previous EPB tunnel excavation experience. The test results have been used to support the planning and implementation of conditioning measures for the excavation and muck pumping processes in the T307 project of the Singapore Thomson East Coast Line.
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R. Duhme / D.g. G. De Oliveira / S. Ferber / H. Nicolet
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