Tilt sliding test to assess the behaviour of conditioned soil with large amount of cobbles

The excavation in alluvial soils is an important field of application of EPB shields since it corresponds to the conditions that can be found in many cities. If conditioning is not optimized, cobbles that are frequently present may move inside the conditioned mass and settle down thus reducing the homogeneity of the muck with an irregular pressure at the face and along the screw and increasing the risk of excavation tool breakage due to the collisions with cobbles. For these reasons it is important that the conditioned soil moves homogeneously. This problem has not been deeply investigated and additional researches could be important for design and machine users. A laboratory test procedure and device that allows to check the interaction between the matrix made of the fine part of the conditioned soil and the cobbles embedded in it is presented and the preliminary test results are discussed.