Using Umbrella Arch Method in Design of Tunnel Lining, Case Study: Water Transfer Tunnel of Kani-sib, Urmia lake

Abstract

The access tunnel of the Urmia Lake for water transfer and restoration project (Kani Sib) is located in the south of West Azerbaijan Province, Iran. Part of this tunnel is located on weak and very loose soil, which in some areas, cannot be stabilized, despite the use of step drilling, and may lead to ceiling collapse, face collapse and even deformation in support system. In these cases, it is necessary to adopt the pre-support method of the umbrella arch. Tunnel stability analysis is one of the important factors in tunnel design and support system. Indeed, the type of support system is chosen according to the required stability and permitted displacement for the tunnel. In the present article, first the permitted displacement for the tunnel is calculated by Sakurai correlation. Then, the ground reaction curve is plotted using the numerical method of finite difference, namely, FLAC3D software, and the convergence-confinement method (CCM) is used to determine the acting instant for the support system. Finally, the safety level of the proposed support system is investigated considering different safety factors. The results of this study indicate that the Sakurai displacement correlation is more reliable than the other graphs presented. The results derived from numerical modeling are verified accurately against visual observation and instrumentation results. A suitable umbrella arch pre-support system with Lattice and Shotcrete support system is recommended. The umbrella arch pre-support system encompasses forepoling pipes of 90 mm diameter with 9 m in length and 2.5 m in overlap length.

Keywords

• umbrella arch
• pre-support
• lining
• flac3d
• forepoling