| In recent years, as the high-speed railway develops rapidly in China, many large cross-section tunnels appears. As for the large cross-section tunnel of high-speed railway which penetrates the geological conditions of soft surrounding rock, it is easy to cause tunnel landslide disasters if excavation of inverted arch is carried out improperly. The excavation of inverted arch has become the key control procedure of the tunnel construction. In view of the fact that the excavation of inverted arch plays an important role on the stability of the whole tunnel. In this paper, through a large number of literature research, and the inductive analysis of the disaster characteristics and influential factors of soft rock tunnel collapse, it is analyzed how the excavation of inverted arch influences the tunnel collapse disaster. The numerical simulation method is used to study the stability of tunnel surrounding rock under the different situations:with excavation of inverted arch, without excavation of inverted arch, excavation length of inverted arch in one step, and closed distance of inverted arch. Based on practical engineering, it is analyzed that excavation of inverted arch influences the surrounding rock deformation of large cross-section tunnel in soft ground area by the way of combining numerical analysis and field tests. Main contents include:Through in-depth study of the characteristics of the tunnel collapse disasters, and the summary of the collapse disaster characteristics of soft rock tunnels, engineering geological conditions, design conditions and construction conditions are the summary of the influential factors causing the soft rock tunnel collapse. Through the detailed analysis of the influential factors causing tunnel collapse, it is elaborated that the mechanical mechanism how the excavation of inverted arch causes the instability of surrounding rock.Based on the size effect of tunnel section, the displacement field of surrounding rock, plastic zone, initial supporting force, and anchor axial force in flat bottomed tunnel and inverted arch tunnel are analyzed under the different surrounding rock conditions from IV-VI level. The results of numerical analysis shows that inverted arch can effectively restrain uplift deformation of the tunnel bottom and extension of plastic zone in surrounding rock, improve the stress state of initial supporting structure. Moreover, the worse the surrounding rock condition, the more obvious the supporting role of inverted arch.In virtue of numerical analysis software FLAC3D, firstly, it is analyzed how excavation length of inverted arch in one step influences the deformation of surrounding rock before and behind tunnel excavation face, and the range of yield area near the excavation face, under the surrounding rock condition from IV-VI level. From the analysis above, the optimization of excavation length of inverted arch in one step is ascertained. Then, it is analyzed how the closed distance of inverted arch influences the deformation of surrounding rock before and behind tunnel excavation face, and the range of yield area near the excavation face, under the surrounding rock condition from IV-VI level, so as to establish the optimization of the closed distance of inverted arch.Take the You Zhu Shan tunnel of the Gui-Guang railway for engineering background, based on the result of site monitoring measurement and numerical analysis at the tunnel entrance section DK80+815?DK80+855 and DK82+840?DK82+960, it is observed that values measured in the field and numerical values are basically identical with the values, which shows the numerical model can perfectly simulate the practical construction situation of You Zhu Shan tunnel. The BiDoseResp function is used to fit the monitoring data of the tunnel vault at the section DK8O+815. It is analyzed that, with the regression equation, how the excavation of inverted arch influences the surrounding rock and supporting structure. |
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