عنوان مقاله [English]
In EPB-TBM tunneling, a positive face control during tunnel excavation is delivered and the tunnel face is supported by pressure from the mass of remolded soil within the cutterhead chamber. EPB TBMs operate more effectively when the soil immediately ahead of the cutterhead and in the chamber forms a plastic plug, which ensures face support. The target properties for extracting soil in an EPB TBM can best be described as a soil matrix exhibiting a soft workable plastic consistency. The behavior of excavated soil from mixing up to extraction depends mainly on the property called workability of conditioned soil. Workability in simple terms can be defined as the ease with which the excavated soil can be mixed with additives, compressed in pressure chamber, flowed freely from the face and finally extracted from screw conveyor. Furthermore, the workability is an indicator for the plasticity of the support media, comparable to the consistency of cohesive grounds and thus a criterion for the applicability of EPB tunneling. The factors which effect the workability of conditioned soil are water content, fine grain, foam injection ratio (FIR). In this study, effecting 10 and 20 percentage of water content and FIR on workability of conditioned soil for EPB-TBM tunneling is assessed with laboratory slump test. The 66 laboratory trials of soil-foam-mixtures were made to investigate the influence of the mentioned parameters on workability of conditioned soil. To analyze the available data using statistical methods, relationships between mentioned parameters and slump test results were investigated. Results of analyzes show that there are a quantitative relation
between water content and the workability for the application of EPB shields. The present study clearly showed that the decrease of water content and FIR became stronger with the decrease of the slump of conditioned soil. Finally, in this study, a new empirical chart, for assessment of and workability of conditioned soil is suggested.