Mechanical Response Analysis Of New High-speed Railway Tunnel In Short Distance And Upper Span Of Existing High-speed Railway Tunnel

At present,the scale of tunnel construction in China has been at the forefront of the world,and has entered a period of equal emphasis on construction and maintenance.In order to meet the needs of social development,the construction of underground engineering is increasing day by day.Due to the limitation of terrain traffic planning and economic cost,more and more near projects are inevitable.The construction of new tunnel has caused multiple stress balances to adversely affect the existing tunnel structure.In severe cases,it has caused diseases such as crack initiation or expansion of existing tunnel structures,resulting in various difficult problems in the construction of new tunnel.In this thesis,the new Pinggongshan high-speed railway tunnel is close to the existing Pingfengshan high-speed railway tunnel as the research background.The comprehensive methods of numerical simulation and field monitoring are used to study the safety problems such as the displacement and stress variation of the existing tunnel structure,the influence of the partition and the crack propagation of the lining structure.The main research work is as follows:(1)FLAC3D numerical simulation software was used to study the displacement and stress variation of existing tunnel structures with strength reduction by standard assessment method under different surrounding rock grades,tunnel space,construction methods and step lengths.The dangerous section and position of the existing tunnel are obtained,which provides a theoretical basis for construction under different conditions.(2)Refer to the relevant literatures and specifications,adopt the zoning displacement criterion suitable for this project and determine the threshold,and use the numerical simulation method to zone the different construction methods and step lengths of the new tunnel under the Ⅲ level surrounding rock.So as to quickly change the construction method,advance the construction period and reduce the cost.(3)By using ABAQUS extended finite element software,30 kinds of working conditions were established under different preset positions,lengths and depth ratios of the existing tunnel lining cross sections to study the crack propagation law and the safety factor K of the remaining section.The influence of cracks on the existing tunnel structure is predicted in advance to ensure the safety of on-site construction.(4)The displacement settlement and convergence deformation law of the existing tunnel lining were compared by on-site monitoring and numerical simulation,and whether crack germination and propagation occurred in the existing tunnel lining was compared,and its safety was analyzed.The results show that the numerical simulation is basically consistent with the on-site monitoring deformation trend,which verifies the accuracy of the numerical simulation method.