Study on the effect of a new construction method for a large span metro underground station in Tabriz-Iran

Abstract

A method for construction of large underground spaces based on a new pre-supporting system is introduced. In this paper Mansour Station, in Line 1 of Tabriz Metro (Tabriz Urban Railway Organization, TURO); Iran has been studied using this method. Mansour Station have some special characteristics such as shallow depth, soft surrounding soil, wide span and heavy street traffic, thus requires a method of underground construction that can control the stability of the underground space and the ground settlement. This method includes a pre-supporting system that is called Concrete Arch Pre-supporting System (CAPS). Construction of CAPS is mainly based on construction method of old Iranian small water tunnels, Quanat, which is generally fast and more economical than usual methods such as forepoling. CAPS is a rib like underground structure consists of concrete piles and arch beams constructed around a proposed underground space prior to its constructions. This method has been utilized in several underground stations in Tehran Metro since 2002 and can be used for any large span underground spaces in similar ground conditions. Numerical modeling is used to simulate all the construction stages and analyze the ground behavior. The results of the modeling show that CAPS reduces the ground surface settlement and enhances the ground stability. Dimension of arch beams and their spacing has also notable effect on the ground deformation.