Research On Deformation Control Effect Of Pipe Shed Pre-support In Nan-chong Railway Airport Tunnel

With the further development of transportation construction,most of the roads and railway tunnels planned and under construction are in weak and broken stratum.Due to its low strength and poor self-stability,weak surrounding rock often presents problems such as large deformation and high cost in the construction of soft rock tunnels.The pipe shed advanced pre-support technology is widely used in soft rock tunnel engineering because of its long reinforcement distance and low construction cost.Based on the Nanning-Chongzuo Railway Airport Tunnel,this paper studies the effect of pipe roof pre-support on soft rock tunnel deformation control through numerical simulation calculations.The main research work is as follows:(1)By consulting relevant materials,summarizing the definition of weak surrounding rock,analyzing and discussing its characteristics,combined with the classification criteria and influencing factors of weak surrounding rock,the treatment measures that may be problematic in the construction of weak surrounding rock tunnel are studied.This paper summarizes the structure form of pipe shed pre support,and the design parameters of pipe shed construction are discussed,which provides a basis for the subsequent study of the relationship between pipe shed design parameters and support effect.(2)According to the theory of surrounding rock pressure of shallow tunnels,a two-parameter Pasternak elastic foundation beam is established.Through Matlab programming and calculation,the deflection equation of the tunnel pipe roof of Nanning-Chongzuo Railway Airport is analyzed,and the bending moment,shear force and deflection law of the pipe roof are analyzed.(3)Combining the actual Nanning-Chongzuo railway airport tunnel project,the influence of pipe canopy on surrounding rock and support is analyzed by using finite element software.The results show that the pipe shed support can effectively control the settlement of surrounding rock vault,and the settlement development trend is slow and the convergence is good.Summarize the deflection,bending moment and shaft force response law of the pipe shed under the pre-support of the pipe shed,and the numerical simulation results are compared with the results of the two-parameter elastic foundation beam model.The two results are in good agreement,which shows that the mechanical model of the pipe shed of the elastic foundation beam in this paper is reasonable.(4)Combining the geological survey data of the tunnel site,the optimal combination of the three supporting parameters of the pipe roof in the Nanning-Chongzuo Railway Airport is analyzed.The results show that the settling amount of the vault roof under the two working conditions of the excavation footage of 0.6 and 1.2m Reduced by 36.4%;the diameter of the pipe roof was improved from 89 mm to 108 mm,and the suppression of the dome settlement increased by 15.3%.Compared with the improved excavation footage,its effect on the control of the dome displacement was limited;although the 0.3m arrangement was consistent with the dome settlement The effect is the best,but the ring spacing of the pipe shed is too small,which means that the number of steel pipes is too large,and the economic cost is unreasonable.Considering the optimal value of the ring spacing is 0.4m.