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Elyasi A.,Tarbiat Modares University | Javadi M.,Shahid Bahonar University of Kerman | Moradi T.,Consultant Engineering Institute of Iman Sazan | Moharrami J.,Consultant Engineering Institute of Iman Sazan | And 2 more authors.
Bulletin of Engineering Geology and the Environment | Year: 2015

In order to prevent the collapse of ceilings and walls of large tunnels, especially in difficult geological conditions, either a sequential excavation method (SEM) or ground reinforcing method, or a combination of both, can be utilized. The first part of the adit tunnel in northwestern Iran is being drilled in alluvium material with very weak geotechnical parameters. Despite applying an SEM in constructing this tunnel, analyzing the numerical modeling done using FLAC3D, as well as observations during drilling, indicate tunnel instability. To increase operational safety and to prevent collapse, a pre-support system was designed and implemented. The results of the numerical modeling accompanied by monitoring during operation, as well as the results of instrumentation, indicate the efficacy of this method for preventing collapse in alluvium material along the tunnel route. Modeling the behavior of the umbrella arch shows that the location of the maximum compressive force will change with a change in the tunnel arc location. Moreover, displacement, force and moment exerted on the pipes will change during drilling steps according to a certain pattern. © 2015 Springer-Verlag Berlin Heidelberg


Elyasi A.,Tarbiat Modares University | Moradi T.,Consultant Engineering Institute of Iman Sazan | Moharrami J.,Consultant Engineering Institute of Iman Sazan | Parnian S.,Consultant Engineering Institute of Iman Sazan | And 2 more authors.
Structural Engineering and Mechanics | Year: 2016

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 (2L100x100x10 mm) in both box profile and tee array as an alternative section to pipe fore-poling system while neither L80x80x8 mm nor 2L80x80x8 mm can sustain the axial and shear stresses exerted on pipe fore-poling system. Copyright © 2016 Techno-Press, Ltd.

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