The Italian Approach for the Evaluation of the Potential Ecotoxicity of Spoil Material in EPB Excavation

Earth Pressure Balance TBM is currently the most used technology in mechanised tunnelling. The use of EPB-BM requires soil conditioning additives among which the most important is foam to optimise soil properties, stabilise the tunnel face, reduce wear on the TBM equipment and prevent clogging of the screw conveyor, thereby improving operational efficiency. The various parameters for which foam is used in real excavations should be studied in detail in site-specific studies at the design stage, considering the geomechanical and environmental aspects. This is because the additives can contain surfactants (e.g. anionic sodium lauryl ether sulphate, or SLES) as the main component, and these require time to degrade when the spoil material is produced. Indeed, although the conditioning ensures the correct working principles of the TBM, only a proper environmental study could lead to the correct manage the spoil material, minimizing the possible risk for the environment due to high concentrations of SLES in soil debris, in particular in deposits where there is a direct contact with water bodies. In this paper, the Italian approach to this topic is presented, the most used ecotoxicological tests are discussed, integrated in a proper excavated material management procedure.