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Geomechanics and Engineering
  Volume 11, Number 4, October 2016 , pages 471-492

Stability assessment of tunnel face in a layered soil using upper bound theorem of limit analysis
Nima Khezri, Hisham Mohamad and Behzad Fatahi

    Underground tunnelling is one of the sustainable construction methods which can facilitate the increasing passenger transportation in the urban areas and benefit the community in the long term. Tunnelling in various ground conditions requires careful consideration of the stability factor. This paper investigates three dimensional stability of a shallow circular tunnel in a layered soil. Upper bound theorem of limit analysis was utilised to solve the tunnel face stability problem. A three dimensional kinematic admissible failure mechanism was improved to model a layered soil and limiting assumptions of the previous studies were resolved. The study includes calculation of the minimum support pressure acting on the face of the excavation in closed-face excavations. The effects of the characteristics of the layers on the minimum support pressure were examined. It was found that the ratio of the thickness of cover layers particularly when a weak layer is overlying a stronger layer, has the most significant influence on the minimum tunnel support pressure. Comparisons have been made with the results of the numerical modelling using FLAC3D software. Results of the current study were in a remarkable agreement with those of numerical modelling.
Key Words
    minimum support pressure; stability; layered soil; upper bound; tunnel
(1) Nima Khezri:
UTM Construction Research Centre (UTM CRC), Block C09, Level 1, Institute of Smart Infrastructure and Innovative Construction, Universiti Teknologi Malaysia, 81310, Skudai, Johor, Malaysia;
(2) Hisham Mohamad:
Civil and Environmental Engineering Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 32610 Perak, Malaysia;
(3) Behzad Fatahi:
School of Civil and Environmental Engineering, University of Technology, Sydney, Australia.

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