Reinforcing effect of FRP multi-step grouting method for NATM tunnel by back analysis method

Abstract

A fiber glass reinforced plastic (FRP) pipe has been newly developed for grouted-reinforcing members and widely used in the tunnel excavation in Korea. The multi-step grouting method using FRP pipe, has the advantage in reinforcing effect and handling of reinforcing members, compared to typical reinforcing methods such as fore-poling and steel pipe reinforced grouting methods. Generally, when excavating tunnel in soft ground, it is grouted through the steel or FRP pipe to reduce the displacement of tunnel. However, in practice it is difficult to evaluate correct design parameter in grouted zone. In this paper, based on the measured data of tunnel 3-dimensional back analyses were employed to evaluate design parameter of grouted zone. From the back analysis results, it could confirm reinforcing effect by increment of elastic modulus in grouted zone and decide the space and length of FRP reinforcing member at the other adjoined tunnel also. This paper presents the reinforcing effect of FRP multi-steps grouting for tunnel by evaluating the change of stress measured on FRP pipe and in the ground, and the displacement of the ground, according to the excavation steps. Measured results are shown that FRP pipes play an important role as reinforcing members in the excavation of NATM tunnel, and keep in the convergence limit of the displacement in tunnel effectively. With consideration of the geology of the construction area and the application of FRP reinforcement grouting based on countermeasure and measurements, the Song-Am tunnel could be constructed safely while suppressing the displacement of tunnel and surrounding ground. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.