Experimental study on the effectiveness of strengthening over-deformed segmental tunnel lining by steel plates

The method of using steel plates to strengthen existing tunnel linings has been widely applied in many tunnel rehabilitation projects around the world. However, the effectiveness of the strengthening resulting from this method is still unclear, especially for conditions when the segmental linings are deformed to a relatively large extent. In this paper, a series of physical model tests conducted in 1-g plane strain conditions were designed to study the strengthening effectiveness of steel plates for over-deformed segmental tunnel linings. The results show that the segmental tunnel linings affected by the ground surface surcharge will deform nonlinearly, as the complex behaviour of the segment joints at different positions lead to a gradual degradation of the tunnel overall performance. Once the deformed segmental tunnel linings were strengthened by steel plates, the stiffness and capacity of the tunnel were improved by 190% and 69%, respectively, compared to those without strengthening. Subsequently, the strengthening effectiveness of tunnels strengthened at different deformation stages are compared quantitatively. It is found that an increase in the tunnel deformation before strengthening led to a decrease in the stiffness and an increase in the total capacity of the tunnel after strengthening, while the increased capacity was less affected.