Long-Term Behavior of Support Elements in NATM Tunnels

Muhammad Usman

Research output: ThesisDoctoral Thesis

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Abstract

The long-time behavior of support elements in New Austrian Tunneling Method (NATM) tunnels was studied by applying the finite element method using new findings from laboratory tests based on 30 years old tunnel support elements. The gradual degradation of reinforced shotcrete support over a period of time, its perpetual deterioration under the inuence of dierent physical, chemical, mechanical and biological agents and ground pressure was simulated by the reduction of Young's Modulus, cohesion and friction angle to study the impact of this reduction on the stress distribution and overall stability of the tunnel support system consisting of rock mass, shotcrete and the inner lining. The degradation of sprayed concrete linings may contribute to destabilization of the rock mass, resulting in increased maintenance costs, reduced service life, as well as a potential safety risk. A three-dimensional finite element model involving dual-lining system consisting of primary shotcrete support, and the inner cast in place concrete liner was modeled using the FE programme ABAQUS. The tunnel excavation was simulated using top-heading, bench and invert techniques with simultaneous installation of the shotcrete support. The emphasis was on the prediction of deformation and stresses acting on the primary shotcrete lining during the excavation in soil modeled with Mohr- Coulomb elasto-plastic material behavior. The material parameters used in the analysis were derived from the 30 years old shotcrete, concrete, steel anchors, and waterproof geomembranes samples from dierent Austrian tunnel sites tested in the laboratories of the Montan University. The samples of the inner lining were tested at the Graz University of Technology. Using a parametric study, dierent deterioration processes were simulated by dening suitable interaction between the shotcrete shell and the ground, and the interaction between the shotcrete shell and the inner liner. Substantiating shotcrete shell deterioration, the progressive increase of stresses in the inner lining and stress dissipation into the surrounding ground was observed. This provided the possibility to illustrate the main attribute of a particular deterioration process on the basis of the obtained stress distributions and displacements of the support elements. The evaluated results furnished important information to devise a virtual relationship governing the quantum of load shared by inner liner and construing practical solutions for dimensioning of inner lining thickness and reinforcement requirements.
Translated title of the contributionLangzeitverhalten von Stützelementen in NATM Tunnels
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Jodl, Hans Georg, Assessor B (external), External person
  • Galler, Robert, Assessor A (internal)
Publication statusPublished - 2012

Bibliographical note

embargoed until null

Keywords

  • NATM
  • support elements
  • long term stability

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