| At present,the total mileage of China's high-speed rail operations ranks first in the world.With the social and economic development of our country and the continuous progress of high-speed railway technology,there will be a large number of high-speed railway investment planning and construction in the future.And we must build many tunnels when building a high-speed railway in the mountains.The geological conditions of mountain tunnels are complicated,especially the geological conditions at the tunnel entrance are terrible.How to ensure the tunnel to enter the tunnel smoothly is a difficult problem to be solved.Relying on the construction background of the pile-arch type open cut tunnel structure section at the entrance of a tunnel of the Chongli branch line of the Beijing-Zhang High-Speed Railway,the dissertation first analyzes and compares the pile-arch type open cut tunnel and the conventional open cut tunnel based on actual engineering.Then,through the two-dimensional plane simulation and three-dimensional simulation,the mechanical performance analysis of the pile-arch type open cut tunnel structure of the opening section is established,and then the entire opening section model is established to study the three-dimensional space stress of the pile-arch type open cut tunnel.Finally,the contents and methods of monitoring and measuring during the excavation of the tunnel structure and the filling process,and the comparison and analysis of the monitoring results and simulations and theories.The main conclusions obtained through the above works are as follows:(1)The pile-arch type open cut tunnel is a new type of open hole structure that can effectively reduce soil excavation,make full use of the foundation pit maintenance structure,and ensure the safety of construction and operation in the weak stratum of the tunnel opening.(2)The horizontal and vertical displacements of the pile-arch type open cut tunnel retaining piles increase continuously as the construction progresses.Its deformation conforms to the "bow" deformation law when the embedded depth is shallow,but its overall displacement is relatively small,and the deformation of the retaining pile meets the construction requirements.(3)The prestressed reinforced concrete transverse brace is the most important link in the entire support system,which is mainly under compression.With the construction of the pile-arch type open cut tunnel,its axial force is gradually decreasing,Therefore,the height of backfill soil should be controlled in actual construction.Derived by consulting relevant literature,extreme safety backfill soil height is about 13.7m.In the actual project of this project,the backfill soil height is relatively small,so the external expansion value of the arch arch foot is also small,and the construction safety is guaranteed.(4)Due to the supporting effect of the surrounding piles and the existence of construction joints,the displacement of the pile-arch type open cut tunnel is less affected by the open-cut and undercut,and the open cut tunnel structure construction,that is,the above-mentioned construction has a little effect about the pile-arch type open cut tunnelfoundation pit and its space structure is reasonable.However,after the backfill soil is covered,the vertical displacement of the pile-arch open cut tunnel structure is increased due to the vertical pressure of the structure,that is,the backfill soil construction is one of the main control points of this method;(5)The field measured data of each structure of the pile-arch type open cut tunnel is not much different from the results of simulation calculation and theoretical analysis.The theoretical analysis and numerical calculation results can predict the construction effect to a certain extent,and then combined with on-site monitoring data can better guide the construction.In general,the pile-arch type open cut tunnel is reasonably stressed,the displacement of each structure is within the safe range,and the safety during construction is relatively high. |
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