Application of Reinforced Ribs of Sprayed Concrete (RRS) in the New Austrian Tunneling Method (NATM)

Theresa Maier

Research output: ThesisMaster's Thesis

Abstract

The research presented herein aims to assess the feasibility of incorporating Reinforced Ribs of Sprayed Concrete (RRS) into the New Austrian Tunneling Method (NATM). The three following research questions have been addressed: How does the RRS mechanically perform in the given case? What are the limits of RRS regarding the loading capacity? Is it reasonable to apply RRS in the context of NATM with the current state of knowledge about the system? To achieve this, a comprehensive comparison between NATM and the traditional Norwegian Method of Tunneling (NMT) is conducted to delineate their key distinctions and found that the main differences between NATM and NMT are in the rock mass characterization and in the way the rock mass support is designed. Next, the behavior of RRS under load is evaluated with the aim of determining how it could be implemented within NATM in terms of mechanical behavior based on the current state of knowledge of RRS. For this evaluation, two tunneling projects serve as case studies: the Fornebubanen project, where on-site data related to installation and design were gathered, and the Frøyatunnel, which serves as the primary data source for analysis. The analysis of the RRS lining system is carried out through three distinct approaches. First, analytical calculations using the Confinement Convergence Method (CCM) are conducted. Then, numerical modeling via RS2 software is performed to simulate the system's behavior. Lastly, structural design calculations are performed. To use a support system within the NATM, the mechanical behavior of the system has to be well understood. The analysis shows that existing knowledge about the mechanical behavior of RRS is limited, and its design and implementation predominantly rely on empirical data with limited measurement data available. This results in the need for numerous assumptions during analysis. The results show that the analytical, numerical, and static calculations yield consistent results; however, these analyses require simplifications that introduce limitations. The true consequence of the results due to these simplifications cannot be determined within the scope of this thesis. With the methods used in this thesis, neither the mechanical behavior nor the load limit can be determined properly, both of which are required for NATM. The conclusion of this work is, therefore, that the current state of knowledge about the mechanical behavior of RRS is insufficient for its application of NATM. An application of RRS in Austria is additionally prevented, among other reasons, by the current prohibition on the use of steel fibers as shotcrete reinforcement.
Translated title of the contributionAnwendung von Reinforced Ribs of Sprayed Concrete (RRS) bei der Neuen Österreichischen Tunnelbaumethode (NATM)
Original languageEnglish
QualificationDipl.-Ing.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Villeneuve, Marlene, Supervisor (internal)
  • Holter, Karl Gunnar, Supervisor (external), External person
Award date15 Dec 2023
Publication statusPublished - 2023

Bibliographical note

embargoed until 21-11-2028

Keywords

  • RRS
  • NATM
  • NMT
  • CCM
  • Numerical modeling

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