Research On Advanced Geological Prediction Technology Of Tunnel Based On Elliptic Polarization Characteristics Of Rayleigh Surface Wave

In the construction of tunnel in China,the proportion of deep buried and long tunnels is increasing,complex and variable geological conditions and unpredictable geological conditions have brought great difficulties.Due to the limitation,conventional geological survey techniques in the tunnel area cannot be probed all during the tunnel design stage.Therefore,the tunnel geological prediction technology as a supplement to the additional technology has an important role for the safe construction of the tunnel.In this paper,we researched the elliptical polarization characteristics of the Rayleigh surface wave in the tunnel seismic wave field,the related research is carried out through numerical simulation and field test.A total of the following aspects are carried out:(1)Based on the finite element software ANSYS,the 3D simulation of the tunnel seismic wave field is implemented.By comparison,the appropriate element type,mesh size of dispersion effect,and the influence of the boundary on the simulation result is analyzed.The simulation shows that when the meshing is set to 0.5 m,the effect of the dispersion effect can be eliminated,and the viscoelastic boundary can be well absorbed in the three-dimensional simulation.(2)Three models of uniform model,low-velocity belt model and cavity model are selected to simulate the full-wave field.Seismic time profiles and snapshot are extracted from them,and the elliptical trajectories and long-short-axis curves of different models are fitted.Rayleigh waves are respectively applied.The elliptical polarization characteristics generated by uniform medium,low-speed band and cavity are compared and analyzed.(3)Field hammer test study.Based on the single receiver low-frequency three-component seismic records collected in the tunnel,the elliptical trajectory curve and the long and short axis curves are fitted,and the elliptical polarization characteristics of the Rayleigh wave are analyzed,and the geological structure in front of the face is reversed,the interpretation results of the geological radar and the TSP are compared to verify the feasibility and reliability of the tunnel surface wave prediction technology.The research results in this paper show that the single-point observation system of excitation and reception can use the elliptical polarization characteristics of Rayleigh wave to carry out tunnel geological prediction,and broaden the application range of Rayleigh wave in tunnel engineering.It also proposes a new idea for the current tunnel geological prediction technology,which has a positive impact on the theoretical improvement of the discipline and the development of technology.