Performance-based Re-use of Tunnel Muck as Granular Material for Subgrade and Sub-base Formation in Road Construction

Large volumes of muck are produced in the Alpine Region and bordering areas as a result of new road and railway construction. For example, in Austria every year approximately 32*10^6 Mg of muck are produced from tunnelling activities. In the near future, many other initiatives along the European corridors will lead to further construction activity, with an inevitable increase in the environmental problems related to the use or disposal of the muck generated. Therefore, there is a clear opportunity for the extensive re-use of muck due to the high demand for granular materials (about 3 billion tonnes in Europe, only 5% of which comes from recycling), the depletion of existing quarries (approximately 24,000 in Europe), and the environmental constraints preventing or delaying the opening of new quarries. In this scenario, a new approach to the re-use of muck is both necessary and timely. Although many typical defects deriving from its geological nature and/or from the extraction techniques employed may lead to its rejection as an aggregate, these same defects are of less importance in embankment, subgrade and sub-base construction in transportation infrastructures and, indeed, in most cases they can be mitigated by granular or chemical stabilization. The investigation described here embraces this philosophy. Starting from the chemical physical characterization of seven different mucks derived from tunnelling activities on the Italian side of the Alps, the paper aims to explore the potential benefits deriving from their re use as a construction material. The test methods used all adhere to prescriptive and performance based construction specifications. Notwithstanding the unfavourable geological origin of some of the considered materials, they all exhibited mechanical properties that would encourage their almost complete re-use in infrastructure construction projects.