1 BACK-CALCULATED INTERACTING LOADS ON PIPES OF PIPE UMBRELLA SUPPORT SYSTEMS Günther M. VOLKMANN (1) Florian KRENN (2) (1) ALWAG Tunnelausbau Ges.m.b.H., Wagram 49, 4061 Pasching/Linz, AUSTRIA (2) GEOCONSULT India Pvt.Ltd., Plot 473, Ind.Est., Udyog Vihar, Ph.V, 122016 Gurgaon, INDIA Keywords: pipe umbrella support, canopy tube support, soft ground tunneling INTRODUCTION Geomechanical design according to the Austrian Guideline (ÖGG, 2001) distinguishes between rock mass behavior and system behavior. Whereas the rock mass behavior (or ground behavior) describes the behavior of a fictitious full-face excavation without support measures and consequently failure modes of an unsupported rock mass, the system behavior considers the interaction of ground and installed support measures. The geotechnical monitoring performed during tunneling observes the system behavior; especially in soft ground tunneling since it is never intended to reach the limit state of ground failure during any construction phase. Therefore, all analyses are performed based on a monitored system behavior, meaning the contribution of installed support measures to the system behavior has to be assumed with simplified structural models. This paper involves conclusions drawn from on-site monitoring results. This includes the evaluation of geodetic surveys on the surface and horizontal in-place inclinometer chains installed in a pipe umbrella support. The objective of this paper is to analyze the mode of loading and its effect on the overall system behavior for pipe umbrella supports during tunneling. PROJECT DESCRIPTION The Brenner corridor is part of the new North-South European rail link for high-speed trains and combined transport services connecting Munich in Germany and Verona in Italy. A part of this route follows the Lower Inn Valley in Austria, which is narrow and densely populated with towns lined up along the Inn River. For this reason, 83 percent of the 41 km long Lower Inn Valley route will run underground. The new route includes the tunnel Vomp – Terfens, which is about 8 km long and is constructed through different types of ground; competent rock and soft ground (quaternary sediments such as ground moraine and gravel). The applied support measures varied from 150 mm steel fiber – reinforced shotcrete in the hard rock sections (dolomite) to 300 mm reinforced shotcrete lining with a pre-support system consisting of face bolts and double layered pipe umbrellas in the sections with low overburden and layers of potentially unstable gravel. Volkmann, G.M. & F. Krenn, 2009. Back-Calculated Interacting Loads on Pipes of Pipe Umbrella Support Systems Proc. of the ITA-AITES World Tunneling Congress 2009, Safe Tunnelling for the City and for the Environment, May 23-28 2009, Budapest, Hungary; ISBN: 978 963 06 7239 9