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  Effects of Soil Conditioning on Ground Control and Performance of EPB Shield

  Earth pressure balance (EPB) machines are designed for the construction of tunnels in soft grounds. These machines use the excavated soil in a pressurised chamber to apply a support pressure to the tunnel face. If the support pressure is not constant, the varying pressure inevitably leads to collapse of the ground. Effective soil conditioning significantly improves ground control and machine performance. This paper presents experimental investigations and laboratory testing using a tailor-made mixer equipped with torque meter which simulates the conditioning of the excavated soil to measure the energy consumption of the system and improve the machine performance. The tested soils were medium-grain sands with varying amounts of clay and the tested conditioned mixtures were obtained with different water contents and amounts of foam. A flow table test was also used to analyse the global characteristics of the conditioned soils. The tests have shown that the proposed laboratory procedure permits a quantitative comparison to be made between different conditioning amounts and agents based on measurable parameters.

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