## 4 Rock Characteristics of Quartz Phyllites and Bundner Schists  
### Rock Quality of the Source Rocks  
In general, if recycling of the excavated material is considered, the prospects depend mainly on two factors. Fundamentally, the (1) type of source rock determines the quality of the excavated rock aggregate. While in the planning phase of a tunnel, the local geological subsoil is investigated in detail, the tunnel route is determined in accordance with other criteria than the recyclability of the source rock: next to technical framework conditions, like tunnel gradient, building logistics and conservation concept, legal issues and political decisions are of primary importance [16; 17; 19]. Thus, the existing rock material is applied to an optimum utilization at the given conditions by adapting the sorting and processing to the local conditions. Furthermore, the (2) method of tunnel excavation--drill and blast or tunnel boring machine driving--affects the geometric properties and therefore significantly influences the extent of recycling, see Section 4.2. In the case of the Brenner Base tunnel, the a priori uncertain rock units of the Innsbruck Quartz Phyllites and Bundner Schists were evaluated regarding its recycling potential. Quartz Phyllites and Bundner Schists are metamorphic rocks showing a significant schistity due to quite large amounts of sheet silicates as well as rather low to moderate rock strength. Due to this, rock material from the Bundner Schist and Quartz Phyllite was tested including large scale processing experiments. A wide range of rock examinations concerning the geometric, physical and chemical properties as well as  
Figure 3: Simplified geological cross section through the Brenner Base tunnel according to [29]. intensive concrete production and testing were herein performed. The feasibility study finally showed the suitability for recycling of calcareous rocks of the Bundner schist unit [30; 31]. As a first step, excavation material derived by drill and blast tunneling of the Innsbruck Quartz Phyllite as well as the calcareous Bundner Schists--the latter were obviously most suitable for processing and recycling--was tested. Physical, chemical and geometric rock parameters were obtained with regard to is suitability as aggregate for concrete (Table 1) [25; 31]. As shown in Table 1, water absorption, as an indication of rock porosity and aggregate frost resistance, is low in the case of the Quartz Phyllite rock material. This means that only very little water is absorbed by this rock type, unlike the Bundner Schist rocks, which show rather high absorption values on first examination, but finally, without having a negative impact on freeze/thaw resistance, attain top class F1 in both cases (according to European standard EN 12620 'aggregate for concrete'). The compression test results for the Quartz Phyllite rock type, as well as point load testing and Schmidt hammer test as indirect compressive strength test methods, show rather low rock strength, only marginally acceptable for many applications. In the case of the Bundner schists, rock strength is mediocre, but still satisfactory. Both rock types, especially the Quartz Phylites, show a rather low E-modulus compared to standard aggregate meaning that concrete made of these aggregates will also have rather low E-modulus values. Concerning elastic deformation of, e.g., concrete linings, this is an advantage because of reduced crack development, though also suffering higher deformation rates, see [22]. Resistance against impact and abrasive loads, expressed by the Los Angeles (LA) value (according to the European standard EN 1097-2), in both cases is mediocre, possibly causing increased loss of material as fines during material processing because of increased crushing.