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Geomechanics and Engineering
  Volume 14, Number 5, April10 2018, pages 479-489

A hybrid MC-HS model for 3D analysis of tunnelling under piled structures
Ahmed F. Zidan and Osman M. Ramadan

    In this paper, a comparative study of the effects of soil modelling on the interaction between tunnelling in soft soil and adjacent piled structure is presented. Several three-dimensional finite element analyses are performed to study the deformation of pile caps and piles as well as tunnel internal forces during the construction of an underground tunnel. The soil is modelled by two material models: the simple, yet approximate Mohr Coulomb (MC) yield criterion; and the complex, but reasonable hardening soil (HS) model with hyperbolic relation between stress and strain. For the former model, two different values of the soil stiffness modulus (E50 or Eur) as well as two profiles of stiffness variation with depth (constant and linearly increasing) were used in attempts to improve its prediction. As these four attempts did not succeed, a hybrid representation in which the hardening soil is used for soil located at the highly-strained zones while the Mohr Coulomb model is utilized elsewhere was investigated. This hybrid representation, which is a compromise between rigorous and simple solutions yielded results that compare well with those of the hardening soil model. The compared results include pile cap movements, pile deformation, and tunnel internal forces. Problem symmetry is utilized and, therefore, one symmetric half of the soil medium, the tunnel boring machine, the face pressure, the final tunnel lining, the pile caps, and the piles are modelled in several construction phases.
Key Words
    tunnelling; soil-structure interaction; piled structure; strain-hardening; finite element; three-dimensional analysis
Ahmed F. Zidan: Department of Civil Engineering, Faculty of Engineering, Beni-Suef University, Salah Salem Street 62511 Beni-Suef, Egypt

Osman M. Ramadan: 1.) Structural Engineering Department, Faculty of Engineering, Cairo University, Giza, Egypt
2.) Higher Technological Institute (HTI), 10th of Ramadan City, Egypt

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