Using the slump test to assess the behavior of conditioned soil for EPB tunnelling

In order to extend the application field of Earth Pressure Balance (EPB) tunnel machines to various soil conditions, the soil to be excavated has to be treated with additives in order to modify its mechanical properties, changing it into a plastic paste. Sometimes the grain size distribution is also changed with the use of fine-sized materials. The performance of the conditioned soil should be evaluated with tests that are able to describe its mass behavior, but very little research has been carried out in this field. Often the choice of the conditioning agent set and its control during the excavation is made on a trial-and-error basis during the excavation process. The slump cone test performed on conditioned material is a fast and lowcost way of checking this behavior both in the laboratory and on the job site. The results of a test program on different conditioned non-cohesive soils using the slump cone test are presented and discussed. The influence of the water content and the amount of conditioning foam has been studied, and the feasibility of this type of test for the control of EPB conditioned soil has been assessed.