|Application and optimisation of tunnel excavation material shown by the example of the Brenner Base Tunnel
This work is concerned with the research question of the recycling of various rock types that are accumulated during the course of the tunnelling work of the Brenner Base Tunnel. In the environmental impact assessment, a forecast concerning the possible recycling magnitude is stating that only about 6 % of the excavated rock material can be reused as aggregates for concrete and approximately 15 % as filling materials. However, this would mean that around 79 % of the rock material has to be deposited – at least without any further treatment of the excavated material. However, the aim must be the maximal recycling by optimisation of the processing method and material management concept. In fact, the general aim is to find the optimal utilization for the excavated rock, either as aggregate for concrete, upper and lower unbound base layers or hydraulically bound base course in road construction or as technical fill material. For that reason, the rock material must satisfy various requirements to be easily processed and to guarantee operational feasibility and durability of the structure.
Therefore, data concerning the geological condition of the Brenner massif were prepared as a first step. Moreover, the current state of knowledge regarding the recycling of tunnel excavation material was prepared and introduced on the basis of the material management of the Lötschberg and Gotthard base tunnel. Furthermore, the legal and regulatory framework regarding the reuse of excavation material was illustrated in detail. Subsequently rock properties of excavation material of the Brenner Base Tunnel were investigated. Three types of lithologies have been considered: the “Innsbrucker Quarzphyllit” (phyllite), the “Bündnerschiefer” (schist) and the “Zentralgneis” (gneiss). The investigation involved the evaluation of mineralogical and petrological characteristics as well as the testing of geometrical, physical and chemical properties. Afterwards an evaluation concerning various recycling possibilities was conducted and the suitability of the different rock types with regard to their use as filling materials, unbound and hydraulically bound layers, sealing layers, and the manufacture of aggregates for concrete using different processing methods examined. Standard concrete tests and special investigations were performed with regard to the tensile behaviour and fracture energy of various concrete mixtures by using excavated material as aggregate for concrete. Concrete admixtures and additives as well as fibres (steel- and PP-fibres) were used to manufacture different concrete compositions.
One important aspect of this work is a general examination of the ecological balance achieved by the recycling of tunnel excavation material with a proposal to improve it by using ecofriendly CEM V-cements. Recommendations and framework conditions are given regarding the evaluation and optimal recycling of the rocks of the Brenner Base Tunnel.
A description of the implementation and application into practice based on the findings completes this volume: in 2014, a material-processing plant was installed at the access tunnel Wolf in Steinach am Brenner. The preparation of the excavated raw material (Bündnerschiefer) is carried out near the tunnel portal. The treated rock material is used for aggregate for shotcrete and structural concrete as well as for gravel used as drainage material.