Soil conditioning tests of clay for EPB tunnelling

Tunnelling with earth pressure balance - tunnel boring machine (EPB-TBM) in clayey soil requires a careful conditioning to reduce the effect of clogging and stickiness. In the last decade, many researches have been carried out to understand how to reduce these negative behaviors using conditioning agents, and different laboratory test procedures have been proposed using both powdered clay and clay chips to quantify and assess the effect of conditioning in terms of reduction of clogging and stickiness. In this paper a review of the various proposed tests is presented. Unfortunately, it can be seen that no unified assessment method on the soil conditioning is available and therefore the designers do not have consistent data on which their choices are based. The present research proposes a laboratory test methodology to study clay conditioning taking both the behavior of chips and powdered clay into account. The proposed procedure has been applied on two different clays, and the test results are presented and discussed to show how the proposed methodology could be applied.