Study On Deformation Mechanism And Calculation Method Of Overlying Pipeline During Excavation Of Shallow Buried Loess Tunnel

With the development of traffic engineering in the central and western regions of China,the total length of tunnels in the loess area is increasing,and it is inevitable that there will be spatial intersection with existing natural gas pipelines,and the phenomenon of tunnels crossing existing pipelines will occur.At this time,the disturbance caused by the tunnel construction in the surrounding formation will inevitably lead to additional deformation and internal forces of the adjacent pipeline,and if the pipeline deformation is too large,it will affect its safety.Therefore,it is necessary to analyze the interaction mechanism between tunnel excavation and adjacent existing pipelines,reasonably calculate pipeline deformation,and accurately assess the impact effect of tunnel construction on existing pipelines.Based on the above factors,this paper systematically studies the impact and calculation of shallow buried loess tunnel construction on adjacent pipelines based on the engineering properties of loess in western Henan Province through the engineering background of the Kelewan Tunnel under the Kelewan Tunnel in Henan Province,and through the combination of indoor test,numerical analysis and theoretical calculation.The main contents and conclusions are as follows:(1)Through the triaxial shear test relying on the structural loess of the project,by analyzing data of the test,the relationship between the structural parameter change law,the strength parameter and the structural parameter,and the relationship between the structural parameter and the generalized shear strain in the shear process are obtained.Based on the experimental results,the adaptability of the Mohr-Coulomb constitutive model for loess tunnel excavation is modified and embedded in FLAC3 D.(2)The deformation mechanism of the deformation of the pipeline under the tunnel is studied by using the Mohr-Coulomb constitutive model considering structural attenuation in FLAC3 D software.And the influence of the pipeline burial depth,pipeline diameter,pipe wall thickness,construction method,footage,step length,strength of the first lining and other factors on the deformation of the underground pipeline is analyzed.The results show that the deformation of the pipeline is proportional to the depth of the pipeline,the excavation step and the length of the steps,and is inversely proportional to the thickness of the pipe wall and the strength of the support;the diameter of the pipeline increases,the maximum settlement value of the pipeline decreases,and the minimum radius of curvature increases first and then decreases;the control effect of the settlement of the pipeline in the construction method is from high to low> the CRD method> the CD method> the three-step method.(3)Considering the structural characteristics of loess,the pipe-soil interaction of the tunnel excavation process is simulated by using a two-parameter nonlinear foundation beam model,the control equation of pipeline deformation is obtained,and the analytical solution of vertical deformation of pipeline is obtained by using finite difference and Newton’s iterative method.The accuracy is verified by comparing with numerical simulations,and the influence of pipeline burial depth,pipeline diameter,formation loss rate and other parameters is analyzed.The results show that the maximum vertical deformation of the pipeline increases with the increase of the depth of the pipeline and the loss rate of the formation,and decreases first and then increases with the increase of the diameter of the pipeline.The maximum radius of curvature increases with the increase of the depth of the pipeline and the rate of formation loss,and decreases first and then decreases with the increase of the diameter of the pipeline.(4)The on-site observation test of the under-penetrating natural gas pipeline of the shallow buried tunnel in the loess area was carried out.The vertical deformation monitoring of natural gas pipelines shows that the pipeline deformation is basically in line with the Peck formula.At the same time,the numerical simulation,theoretical calculation and actual measurement data are compared,and it is found that the numerical simulation and theoretical calculation results are basically consistent with the measured data trend,and the pipeline deformation difference is small,indicating that the values and theoretical methods in this paper can predict the deformation of the pipeline under the tunnel and can be used for engineering practice.