Abstract
In recent years, fiber-reinforced plastic (FRP) has been widely used in the reinforcement of concrete structure fields due to its favorable properties such as high strength, low weight, easy handling and application, and immunity to corrosion, and the reinforcing effects with FRP grids on tunnel linings should be quantitatively evaluated when the tunnels encounter an earthquake. The aim of the present study is to estimate the reinforcing effects of fiber-reinforced plastic (FRP) grids embedded in Polymer Cement Mortar (PCM) shotcrete (FRP-PCM method) on tunnel linings under the dynamic load. A series of numerical simulations were performed to analyze the reinforcing effects of FRP-PCM method quantitatively, taking into account the impacts of tunnel construction method and cavity location. The results showed that the failure region on lining concrete is improved obviously when the type CII ground is encountered, regardless the influences of construction method and cavity location. With the increment of ground class from CII to DII, the axial stress reduction rate R σ increases from 13.18% to 48.60% for tunnels constructed by the NATM, while for those tunnels constructed by the NATM, R σ merely varies from 0.72% to 2.11%. R σ decreases from 43.35% to 34.80% when a cavity exists on the shoulder of lining, while decreasing from 14.7% to 0.12% when a cavity exists on the crown of lining concrete. All those conclusions could provide valuable guidance for the reinforcing of underground structures.
Highlights
The dynamic mechanical behavior of underground structures, such as tunnels and underground caverns, is assumed to be better than that of surface structures, some existing tunnels still have been severely damaged by earthquakes in recent years [1,2,3,4,5,6,7,8]
The axial stress on a lining concrete increases with increasing the ground class when a cavity exists on the shoulder of tunnel lining, the slope of fitting curve shows slightly decrement, indicating that the reinforcing effects with fiber-reinforced plastic (FRP) grids increase with the increment in ground class (Figure 15(c))
With the increase in ground class from CII to DII, Rσ decreases from 43.35% to 34.80% when a cavity exists on the shoulder of lining, while decreasing from 14.7% to 0.12% when a cavity exists on the crown of lining concrete
Summary
The dynamic mechanical behavior of underground structures, such as tunnels and underground caverns, is assumed to be better than that of surface structures, some existing tunnels still have been severely damaged by earthquakes in recent years [1,2,3,4,5,6,7,8]. The repair and reinforcement of existing underground concrete structures has become an import part of civil engineering activities. A series of methods have been adopted to effectively improve the integrity of concrete structures in existing tunnels, the typical ones of which are grouting reinforcement method, fiber reinforced shotcrete (FRS) method [9,10,11,12,13], carbon fiber sheet (CFS) method [14,15,16], steel board method [17], and fiber-reinforced plastic (FRP) method [18, 19]. Due to the favorable properties such as high strength, low weight, easy handling and application, and immunity to corrosion, FRP as a strengthening material for the reinforcement concrete (RC) structures has become commonly used in engineering fields. In the reinforcement of mountain tunnel, the FRP grids embedded in Polymer Cement Mortar (FRP-PCM) shotcrete (FRP-PCM method) are typically used. It is noted that the FRP grids should not be damaged during the drilling or Geofluids
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