Proceedings of the World Tunnel Congress 2017 – Large Caverns – Underground solutions. Bergen, Norway. Semmering Base Tunnel – Large Caverns in Challenging Conditions M. Proprenter iC consulenten ZT GesmbH, Vienna, Austria. O. K. Wagner ÖBB - Austrian Federal Railways, Graz, Austria. ABSTRACT: Semmering Base Tunnel, one of the major infrastructure projects in Europe, consists of two 27.3 km long single-track tunnels, numerous cross passages and a complex underground emergency station with two, more than 420 m deep, shafts. Temporary access is provided by a 1.2 km long access tunnel, with two 120 m subsurface shafts, and two 100 m shafts from the surface. Various types of large caverns are planned, which are either foreseen temporarily for construction purposes such as intermediate access and space for site installations, or permanently for the underground emergency station. The dimensions of the larger caverns are in the range of 25 m by 16 m. The maximum overburden above the caverns is app. 500 m in difficult geological conditions with large fault zones and extensive water inflow, which require complex heading concepts, extensive support measures and partially special ground improvement works such as grouting. The1 appliedINTRODUCTION construction method for the caverns andwhich the is main also parta designated of the single world track heritage tubes site is SEM/NATM whereas the remaining sections are excavateddue to its b engineeringy means of TBM.excellence Works. are ongoing from 2014 until 2026. The new tunnel system will reduce the travel 1.1 General time and improve the travel quality for The Baltic-Adriatic Railway Corridor stretching passenger and freight trains crossing the across Europe connects the Baltic Sea (Gdansk mountainous landscape. The existing in Poland) and the Adriatic Sea (Bologna in Semmering-Railway line will remain in place as Italy). The more than 27 km long Semmering a fallback in case of maintenance works in the Base Tunnel will be one of the major structures new tunnels and for local traffic purposes. In of the Austrian section of this corridor. addition, due to its breath-taking scenery the old The new tunnel system is located railway line forms an often visited tourist approximately 80 km south of the Austrian attraction. capital Vienna, connecting the towns of The total investment costs for the project are Gloggnitz in the federal state of Lower Austria around 3.3 bi. Euros, whereas 1.5 bi. Euros are and Mürzzuschlag in Styria (see Figure 1.). related to the civil construction works. The alignment of the existing railway line Pre-construction works started in 2011 and along this route includes steep gradients and underground excavation commenced in 2014. small radii along numerous tunnels and viaducts All underground excavation works shall be built in the mid-19th century. Nowadays such finished by 2022 followed by the installation of conditions are not compatible to modern rail the secondary lining, track works, electrical traffic in terms of freight or passenger installations and signalling. The envisaged transports. Heavy cargo trains even require the completion date and start for the final operation use of an additional locomotive and the time is 2026. loss for travels along this stretch is considerably high. To improve the situation the new tunnels will replace the existing Semmering-Railway line, 1 Proceedings of the World Tunnel Congress 2017 – Large Caverns – Underground solutions. Bergen, Norway. Figure 1. General location (source: ÖBB) into three separate construction lots designated 1.2 Tunnel and Cavern System SBT 1.1, SBT 2.1 and SBT 3.1 (see Figure 2.). The final tunnel system with a total length of An additional construction lot is foreseen at 27.3 km includes two parallel single track tubes the southern portal including the cut and cover connected by 56 emergency cross passages. The and open cut tunnel section with a total length maximum spacing of the cross passages is of 650 m as well as the modernization of the 500 m. adjacent railway station in Mürzzuschlag. The centrally located emergency station with The excavation works for the underground various caverns and two, more than 420 m deep, structures are carried out by means of NATM ventilation shafts forms the core of the final for a total length of 19 km in the northern and tunnel system. southern parts of the tunnels. At the peak of the Four additional temporary shafts are required excavation works a total of up to 12 NATM to provide access to the underground headings at various locations in the main tunnel construction. Two of the shafts will be tubes will be running at the same time. Due to excavated, starting underground via a 1.2 km the geological conditions for about 8 km in the long temporary access tunnel, located around central section of the main tunnel tubes, TBM 200 m above the main tunnel alignment. Cavern method is applied. The TBM assembly takes systems at the heads of the subsurface shafts place in the underground caverns located in the and at the bases of all shafts accommodate emergency station. installations and logistics for construction In the final tunnels and the permanent purposes. caverns a drained secondary lining will be The spacing of the mostly parallel running installed. In the northern section of the tunnel, tunnel tubes is around 40 m, which is enlarged due to legal reasons, mountain water has to be at the underground emergency station as well as collected below the drainage level and led off in massive fault zones and reduced in the portal separately for further use as drinking water. areas. The alignment of the tunnel is based on a maximum train velocity of 230 km/h with a maximum inclination of 8.4 ‰. Due to the envisaged completion date and for logistical reasons, the main underground works for the tunnels, shafts and caverns are divided 2 Proceedings of the World Tunnel Congress 2017 – Large Caverns – Underground solutions. Bergen, Norway. Figure 2. General layout including construction lots (source: ÖBB) 1.3 General Geology 2 PERMANENT CAVERNS – EMERGENCY STATION Overall the geological conditions of the tunnel system can be described as an area of intense tectonic imbrication. The main units are the so 2.1 Layout called Greywacke zone, the Semmering unit and In order to fulfil the national and international the Wechsel unit. safety regulations an emergency station is Within frequently changing conditions rocks located in the central section of the tunnel consisting of metasediments such as phyllite, system. In case of an accident trains shall stop schist, quartzite, locally sulphate rocks and in the station and passengers shall be transferred metasandstone of various tectonic units as well to rescue trains approaching via the non-affected as carbonate rocks and highly fractured tunnel tube. metamorphic crystalline schist and gneiss will The main structures within the emergency be encountered. The geological units are station are two ventilation and logistic caverns separated by distinct fault zones which formed and an enlarged section of the rescue tunnel, the during the orogenesis with extensive folding so called, rescue cavern. These structures and nappe stacking, leading to an imbricate provide space for logistics and underground site structure. Out of the numerous fault zones the installations during the construction phase and ones consisting of cataclastic fault material with will accommodate ventilation, electrical, and high overburden are especially challenging to safety installations in the final configuration of the construction procedure. Within the the emergency station. The maximum size of carbonate rock formations a considerable water the caverns is about 20 m by 18 m. inflow of up to 300 l/s is expected. The ventilation and logistic caverns are For the design and implementation, the placed perpendicular to the tunnel alignment, tunnel was divided into 33 rock mass zones, of thus stretching over the main tubes and the which more than 40 ground types were rescue tunnel. The rescue cavern and tunnel are evaluated by the geotechnical design team. placed between the running tunnels and Rock mass zones can be characterized as tunnel connection between the two main tunnel tubes is sections, which show similar conditions in terms provided via short escape passages (see Figure of geological structure or units, proportions of 3.). ground types and hydrogeological conditions. A Additional permanent structures within the ground type consists of a rock mass with similar emergency station include the two ventilation in-situ properties, which refers to a volume of shafts, the ventilation tunnels between the main geotechnical relevance for the project. tubes and the rescue tunnel, and two regular The sections, which include caverns, are cross passages. specially designated as individual rock mass For a possible material transport by conveyor zones with their respective ground types belts four temporary logistic passages are considering the enlarged cross sections and foreseen, which are aligned accordingly. mostly differing heading direction. 3 Proceedings of the World Tunnel Congress 2017 – Large Caverns – Underground solutions. Bergen, Norway. The excavation sequence divides the cross section of the caverns into a top heading, two or three benches (depending on the size) and an invert. Out of necessity the application of a sidewall gallery in the top heading was foreseen (see Figure 5.). Figure 3. Scheme - Caverns in emergency station (source: ÖBB/PGST) 2.2 Excavation and support The excavation of the caverns for the emergency station is taking place via the centrally located, larger of the two future Figure 5. Example of excavation steps in cavern ventilation shafts. (source: PGST) The geological conditions in the caverns of the emergency station can be characterized as a The excavations of the particular sections mixture of fractured gneiss and schists of the (top heading, benches or invert) of the cavern Wechsel unit with intersecting cataclastic shear take place at different levels of the shaft zones.