Using Value Engineering in Choosing Small Radius Curve: a Case Study in Mechanized Tunnel of Mashhad Urban Railway Line 3

One of the limitations of mechanized tunnel excavation compared to traditional excavation methods is the creation of tight curve. In addition, excavation problems and limitations are doubled if small radius curves are combined with surface and subsurface obstacles. Typically, there are options available to designers to deal with these obstacles, such as rerouting, proposing remodeling and improvement, and protection plans in the pre-construction phase. According to the initial design of the plan and profile in the western tunnel of the Mashhad urban railway line 3 project, some part of the implementation of the route has faced important challenges, including the synchronization of the 300-meter curve with passing high-rise residential and commercial structures in the region. After studies and investigations, the implementation of the curve with an unusual radius of 270 meters was put on the agenda. Necessary actions have been taken to prevent excavation problems in the tight curve. Some of these actions include the implementation of protection plans for the southern buildings of Ferdowsi Avenue and the Ziba Sazeh building, replacement of brushes and cutting tools, determining the correct position of the key in the ring, special arrangement of inverts and conveyor design that resulted in high quality excavation in the curve. In terms of value engineering, the selection and implementation of a curve with a radius of 270 meters, is equivalent to 20 billion rials in savings.