| Because loess has the characteristics of significant anisotropy,strong permeability,and multiple collapsibility,it often causes large surrounding rock deformation,poor stability of the arch toe,large surface subsidence,and cracks in the surrounding rock during the construction of the loess tunnels,which has caused great troubles to tunnel builders and is also one of the key research directions of scholars.This paper takes the Kelewan Loess Tunnel of the Mianxi Expressway as the research background,mainly based on the engineering design documents,field tests,and numerical simulation analysis methods to study the construction deformation control technology of the shallow loess tunnel underneath the petroleum pipeline,in order to obtain the optimal construction parameters and provide reference and guidance for similar projects in the future.The main content of the paper is as follows:(1)Briefly introduced the engineering background on which the thesis relies,including the geographical location,geological and hydrological conditions,design overview of the Colawan Tunnel,and the existing oil pipelines above the tunnel.Through a large number of literatures,the demarcation method and scope of application of existing shallow and deep tunnels are summarized.(2)Through the physical characteristics test of undisturbed loess,it is known that the water content of the loess is 19.95%,the density is 1.80g/cm~3,the plastic limit is 19.15%,the liquid limit is 30%,the void ratio is 0.822 and the bulk density is 17.64k N/cm~3.Through the indoor consolidation compression test,the vertical natural compressive modulus is 18.22MPa,the horizontal natural compressive modulus is 26.68MPa,and the vertical natural compressive modulus is less than horizontal.Through the triaxial shear test,the horizontal cohesion is118.11k Pa,the internal friction angle is 20.81°,the vertical cohesion is 85.59k Pa,and the internal friction angle is 21.65°.(3)Numerical simulation software is used to compare and analyze multiple simulation results under the CD method and the three-step seven-part method.Compared with the three-step seven-step method,the surrounding rock displacement value,the settlement value of the ground surface and the oil pipeline,the stress value of the sprayed concrete and the oil pipeline produced by the two-step five-step excavation are relatively small,indicating that the two-step five-step method is more suitable for the tunnel excavation(4)Under the CD excavation method,the 0.75m and 1.5m excavation footage were compared and analyzed,and finally according to the simulation results,the tunnel adopts 0.75m excavation footage.When the extrapolation angle of the leading small catheter is 10°,and it is arranged along the range of 120°of the excavation profile,the comparative analysis of the leading small catheters of 3m,4m,4.5m,and 6m is carried out,and finally it was concluded that the reasonable length of the leading small catheter is 4.5m.(5)In order to reduce the impact of tunnel construction on existing oil pipelines,vertical grouting and pre-reinforcement are carried out on the ground around the oil pipeline.When the tunnel model adopts different grouting widths and different grouting depths,comparing the settlement value and stress value of the oil pipeline respectively.The following suggestions are made for the project:(1)The reasonable grouting width is suggested to be 2.44m;(2)The reasonable grouting depth is suggested to be 4m. |
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