Research On Pipe Shed Reinforcing Technology Of Shield Tunneling In Sensitive Area In Sand Pebbles Stratum

With the continuous perfection of urban subway network,subway lines will often need to go through such sensitive areas as bridge foundation,building foundation,railway reserve and so on during the process of construction.Depending on the regional physical engineering of Chengdu metro line 5 that passes down through Baocheng railway’s double cross-sectional area,this thesis adopts methods of materials research,field investigation,field monitoring and numerical simulation calculation to research the pipe shed reinforcement technique of waterrich sand pebble stratum’s metro tunnels that go through the sensitive areas.The main research results are as follows:(1)Through field investigation,the thesis discusses the applicability of common stratum reinforcement method in sand pebble stratum.It also summaries the characteristics of waterrich sand pebble stratum,gives the technical parameters of pipe shed reinforcement in this stratum,and analyzes the unique mechanism of pipe shed reinforcement in this stratum.(2)Using the formula of surface subsidence of double-line tunnel,we discuss the influence factors and critical points of the shape change of the settlement groove in the paper.Through the field monitoring,it is proved that the use of double-layer pipe shed reinforcement can effectively guarantee the safety of shield tunnel through the double cross-sectional area of the railway area.(3)By means of regression analysis of the actual measured value of surface subsidence,the results show that hyperbolic function can generally describe the development process of surface subsidence on the central axis of the pipe shed reinforcement to predict the final amount of surface subsidence on the central axis.(4)The paper analyzes the regularity of the land surface sinking and stratum displacement of single-line tunnel and double-line tunnel after the shield tunneling through numerical calculation.The results show that after the single-line tunneling is completed,the displacement of the stratum is U-shaped and after the construction of the double-line tunnel is completed,the sedimentation trough is offset and the displacement of the stratum is typical shape of glasses.The surface subsidence mainly occurs within 6 times the diameter of the tunnel axis.(5)Using numerical calculation,the paper analyzes the influence of different placement of pipe shed on the surface subsidence.The results show that placing limited numbers of pipe sheds near the place where the stratum loss occurs as near as possible can maximize the effect of the stiffness of the pipe shed and enhance the effect of strata reinforcement.The research results of this paper have not only succeeded in guiding the on-site construction,but also provided valuable engineering analogy data for the design and construction of similar projects in the future,which has important reference significance.