| The railway system in our country develops rapidly in recent years,which is the same to the railway construction in southwest China.Because of the high mountains and lofty hills in southwest China, the proportion of bridges and tunnels is very high in both highway and railway line.With the development and perfection of railway net work gradully,railway tunnel will inevitably encounter the condition of underpassing the operating bridge already existed in line selection.But in the study of tunnel underpassing existing bridge,most studies have focusde on the urban subway and metro station close-spaced existing city bridges,there is no research on railway tunnel underpassing existing continuous rigid frame bridge with 138m pier.Therefore,this paper takes Yakou Tunnel underpassing Chengmendong Bridge, part of newly-built Chengdu-Kunming railway,as the engineering background, and take field research, theoretical analysis, monitoring measurement, numerical analysis as research methods. The main contents are as follows:(1) By simulating the real construction process of Yakou tunnel,the interaction between Yakou tunnel and existing bridge in underpassing area is reflected. The comparison of crown settlement among different analysis sections in the same pilot tunnel shows that the distance between analysis section and bridge pier is closer,the influence of pier load is greater,the antecedent settlement of analysis section is more serious. And the comparison of crown settlement between left pilot(near the bridge pier) and right pilot(away from the pier) at the same analysis sections shows the influence degree of antecedent settlement in left pilot(near the bridge pier) is more serious than that in right pilot(away the bridge pier).(2) The numerical calculation model of Chengmengdong Bridge was established by finite element software named MIDAS/CIVIL,then applying the displacement of pier which was obtained from field data to the numerical calculation model,we can see that the displacement caused by underpassing of Yakou tunnel made different degree of influences on deformation and stress of existing bridge structure.(3) The optimization analysis about construction process of tunnel underpassing existing continuous rigid frame bridge was studied by different construction methods,which pilot excavating fist,different drilling footages,different Different staggers to analy different degree of influences between tunnel and bridge and to find the optimal construction process.Finally,the optimal construction process is the double-side-drift method with left pilot excavating fist, footage of 1.2m and stagger of 14.4m,the crown settlement will be reduced by 26.86% and pier settlement will be reduced by 48.84%.(4)The analysis of engineering preventions about Yakou Tunnel underpassing existing Bridge mainly include tunnel construction technology, reinforcement of surrounding strata near by tunnel and reinforcement of surrounding strata near by bridge. Especially this paper introduced the application of frame beam with prestressed anchor-cable in the process of Yakou Tunnel underpassing existing Bridge for controlling displacement of bridge pier,and had a study on reinforcement effects.Analysis results show that the horizontal displacement of the pier top decreased from 2.69mm to 0.79mm with the reinforcement effect of prestressed anchor-cable, control effect is obvious; the vertical displacement of the pier top decreased from 6.53mm to 6.14mm,control effect is 5.97%. |
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