Lainz Tunnel

During the early twenty-first century, the Austrian government authorised the four-tracking of the Westbahn, which was the nation's most important rail corridor. Accordingly, the section between Vienna and St. Pölten saw the construction of two new tracks on an alignment free from challenging gradients and suitable for high speed operations, which deviated far to the North of the original line. It was along this new route that the Wienerwald Tunnel, which is the single biggest engineering structure, was constructed to convey the line across the Wienerwald mountain range. Its construction facilitated the movement of trains traversing the Westbahn to call at Wien Hütteldorf railway station. carrying two extra tracks for the old Westbahn, which has been operational since December 2008, and direct tracks across the junction continue in the Wienerwald Tunnel, a 13.35 km long twin-track single tube tunnel that was constructed in parallel with the Lainz Tunnel. When combined with the adjacent Lainzer Tunnel, the Wienerwald Tunnel results in trains covering an underground distance of 26 km, making it Austria's longest tunnel. == Construction and operations ==

During the late 1990s, geological surveys were conducted in preparation for the tunnel's construction; these determined that the intended route was feasible in multiple respects, including the local geology, geohydraulogy, and environmental impact. The geology it passes through is primarily composed of layered silt and clay, accompanied by thin layers of sand and gravel. Ahead of the primary excavation activity, numerous vertical wells were driven for the purpose of lowering the local water table. The excavation phase of the Lainz Tunnel's construction involved considerably different methods of construction; while the majority of its length was excavated the New Austrian Tunnelling Method of underground boring, limited portions that featured unfavourable prevailing conditions used the cut-and-cover approach instead. Throughout the construction, sensors were active to monitor conditions such as ground settlement; these were observed to be below set limits throughout the project. Since its completion, the Lainz Tunnel has formed a key civil engineering element for the east–west transit of railway traffic as part of the Magistrale for Europe. Previously, international passenger trains either terminated at Wien Westbahnhof station and passengers travelling eastbound had to make their way to Wien Südbahnhof station, or had to be reversed in Westbahnhof and travelled along a single-track connection through residential areas. In 2014, the new Wien Hauptbahnhof through station replaced this former terminus, and in 2015 most long-distance services were concentrated at Hauptbahnhof, with trains originating from or bound for the Western railway travelling through the high-speed Wienerwald Tunnel and continuing on through the Lainz Tunnel towards Hauptbahnhof and to destinations beyond. The tunnel is also heavily used by freight trains bound for Vienna's central classification yard by way of a branch turning near the eastern end. == References ==