Study On The Deformation Control Of Tunnels With Flat Top And Vertical Wall In Large Section Of Sand-Pebble Stratum Under Through Operating Subway

This paper analyzes the deformation control of tunnels with flat top and vertical walls in large section of sand-pebble stratum under through operating subway,and this paper takes Beijing Wu-Ke-Song underground parking garage pedestrian passage under the existing subway line 1 project as the background.By means of numerical simulation and field measurement,the effect of interlayer soil on underpass construction and the effect of grouting lifting deformation control measures are studied.The main research contents and conclusions are as follows:(1)Study on the influence of interlayer soil on underpass constructionThrough numerical calculation and analysis of the variation rules of the settlement of the arch roof of the newly built tunnel and the subsidence of the existing structure floor in the undercrossing construction of different interlayer soil thicknesses(1?5m),combined with the safety and economic factors,it is concluded that the limit interlayer soil thickness for the undercrossing of this project is about 3m by conventional construction method.Secondly,the influence of different interlayer soil parameters(elastic modulus,poisson's ratio,cohesion and internal friction Angle)on the existing structure and the new tunnel in undercrossing construction is analyzed.Finally,according to the characteristics of stress and deformation of interlayer soil,combined with the characteristics of different section construction methods,the empirical selection of new tunnel section forms under different interlayer soil thickness and surrounding rock strength is given.(2)Study on the control measures of grouting lifting deformationDuring the construction,in order to realize the active control of the existing facility deformation in the sand and pebble stratum,the construction control scheme of the active compound grouting lifting was put forward,and the preliminary design of the active compound grouting scheme was carried out through numerical calculation and simplified mechanical model.Within the scope of deformation control,the existing structure can be actively lifted by reasonable grouting to increase the deformation margin of the existing structure,so as to ensure the safe operation of the existing structure and accelerate the construction progress at the same time.The use of compound grouting pipe can effectively solve the technical difficulties in the complicated and difficult grouting process of multiple hole formation in sand and pebble formation.The field grouting experiment shows that the diffusion effect of slurry+ superfine cement under the same grouting pressure and the core strength are better than that of cement slurry.In order to ensure the excavability of the soil in the tunnel excavation scope,the soil outside the tunnel excavation scope adopts cement +ultra-fine cement slurry,and the grouting slurry in the excavation range shall be mixed slurry of cement + appropriate amount of fly ash,or the water-cement ratio of pure cement slurry shall be increased.When the grouting pressure is 0.5?1.5Mpa,the slurry diffusion range is 0.3?0.6m,and the grouting pressure attenuation is about 20 times.(3)Study on field monitoring dataThrough the comparison and analysis of the monitoring data of the subsidence of the floor of the existing structure and the numerical simulation results of grouting lifting,the lifting effect of the active compound grouting on the existing structure is verified.In a word,this paper studies the deformation control of large cross-section flat-topped straight wall tunnel under sand and pebble stratum,which can provide reference for this project and similar projects.