Structural Engineering and Mechanics

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Efficiency assessment of L-profiles and pipe fore-poling pre-support systems in difficult geological conditions: a case study

  • Elyasi, Ayub (Department of Mining Engineering, Tarbiat Modares University) ;
  • Moradi, Taher (Consultant Engineering Institute of Iman Sazan) ;
  • Moharrami, Javad (Consultant Engineering Institute of Iman Sazan) ;
  • Parnian, Saeid (Consultant Engineering Institute of Iman Sazan) ;
  • Mousazadeh, Akbar (Department of Civil Engineering, Islamic Azad University of Naghadeh) ;
  • Nasseh, Sepideh (Department of Geology, Ferdowsi University of Mashhad)
  • Received : 2015.09.25
  • Accepted : 2016.02.11
  • Published : 2016.03.25
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Abstract

Tunneling is one of the challenging tasks in civil engineering because it involves a variety of decision making and engineering judgment based on knowledge and experience. One of the challenges is to construct tunnels in risky areas under shallow overburden. In order to prevent the collapse of ceilings and walls of a large tunnels, in such conditions, either a sequential excavation method (SEM) or ground reinforcing method, or a combination of both, can be utilized. This research deals with the numerical modeling of L-profiles and pipe fore-poling pre-support systems in the adit tunnel in northwestern Iran. The first part of the adit tunnel has been drilled in alluvial material with very weak geotechnical parameters. Despite applying an SEM in constructing this tunnel, analyzing the results of numerical modeling done using FLAC3D, as well as observations during drilling, indicate the tunnel instability. To improve operational safety and to prevent collapse, pre-support systems, including pipe fore-poling and L-profiles were designed and implemented. The results of the numerical modeling coupled with monitoring during operation, as well as the results of instrumentation, indicate the efficacy of both these methods in tunnel collapse prevention. Moreover, the results of modeling using FLAC3D and SECTION BUILDER suggest a double angle with equal legs ($2L100{\times}100{\times}10mm$) in both box profile and tee array as an alternative section to pipe fore-poling system while neither $L80{\times}80{\times}8mm$ nor $2L80{\times}80{\times}8mm$ can sustain the axial and shear stresses exerted on pipe fore-poling system.

Keywords

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