Technical and economic study of using a hollow guiding rod to connect segments in mechanized tunneling of Mashhad Metro Line 3 tunnel

More recently, the demand has been raised for application of segmental tunnel lining in long and deep tunnels in rock beds and also shallow tunnels in soft ground, particularly in urban areas. From technical and economic aspects, proper dimensioning and connecting of the segmental linings have always attracted the interest of many designers in the field of tunneling. The guiding rods are placed in the horizontal joints of the segment to make the segment easier to install and to provide shear strength at the joint. In this article, first, the types of joints in tunnel segments are studied and how the connections in these joints work are discussed. Next, the performance of the guiding rod is examined and the operation of the guide rod in the tunnel is investigated. For this purpose, the tunnel is first modeled with the real geotechnical conditions of the ground from the metro terminal to Abuzar town station in plaxis2D software and the values ​​of axial and shear forces in the tunnel structure are obtained. Based on the outputs of the plaxis2D model, the amount of shear strength borne by the cross section of the segment and the guide rod is presented. Abacus software is used to analyze the behavior of the guide bar and the output of this model shows that the solid and hollow guiding rods have linear behavior and the hollow guiding rod can also be used for this part of the tunnel route, which can effectively reduce construction costs.