Tunnel spoil classification and applicability of lime addition in weak formations for muck reuse

•A classification of the spoil types from tunnel excavation is proposed.•Possible muck reuses after on-site or plant treatments are classified.•A case history concerning muck from soil conditioning operations is discussed.•The laboratory assessment of spoil properties after treatments is reported.•The proposed method is found reliable in identifying reuse patterns.

Tunnel construction planning requires careful consideration of the spoil management part, as this involves environmental, economic and legal requirements. In this paper a methodological approach that considers the interaction between technical and geological factors in determining the features of the resulting muck is proposed. This gives indications about the required treatments as well as laboratory and field characterisation tests to be performed to assess muck recovery alternatives. While this reuse is an opportunity for excavations in good quality homogeneous grounds (e.g. granitic mass), it is critical for complex formation. This approach has been validated, at present, for three different geo-materials resulting from a tunnel excavation carried out with a large diameter Earth Pressure Balance Shield (EPB) through a complex geological succession. Physical parameters and technological features of the three materials have been assessed, according to their valorisation potential, for defining re-utilisation patterns. The methodology proved to be effective and the laboratory tests carried out on the three materials allowed the suitability and treatment effectiveness for each muck recovery strategy to be defined.