The comparison between steel bolts and plastic dowels in axial and radial segments, Case study: The tunnel of "A" Line in the Qom metro

The current study compares the quality and speed of installing the ring segments in TBM tunnels with two different connection types. The TBM tunnel of the “A” line in the Qom metro Project was selected. Two different types of segment rings with bolts and dowels were used with some modifications in casting bodies. Common deficiencies in TBM tunnels are the existence of the gap and uneven surface between two adjacent segments with bolted connections that lead to water penetration to the tunnel and inappropriate lining surfaces. To resolve these deficiencies, one segment casting was modified from bolted form to dowel form and then installed on the selected tunnel. Investigations on installed segments showed a significant decrease in gaps and uneven surfaces as well as the fracture segments. The fractures in segment edges and bodies decreased 75% and 50%, respectively. Also, the time of installation of the ring with dowels was 11% decreased. It finally showed the higher quality of installation that decreased the penetration, amount of repairing materials, the time of installation, and the cost. Finite element analysis was done to ensure desirable load carrying capacity and appropriate stress propagation between the devices and concrete segments. The results showed that the dowel connections had better behavior. Finally, the modification of steel bolted connection to plastic dowels is recommended in TBM tunnel projects.