The Effect Of Tunnel Embedded In Layered Site On Earthquake Response Of The Ground And Buildings Along The Subway

Some study reveals that the existence of subway influences the design earthquake along it, and so influences the earthquake security of the existing structures on the ground as a result. It is of great value and theory purpose to evaluate this influence quantitatively and earthquake security of the existing structures. Essentially speaking, the influence of the subway to the existing structures on the ground and the earthquake along it is the scattering of the elastic waves subject to the subways.Using the dynamic FEM, the paper gives the scattering problem of the subways to the earthquake waves in the isotropic and layered half-space. The factors, such as the horizontal incident angle, vertical incident angle, embedded depth, incident frequency of the elastic waves, stiffness of the layer, thickness of the layer, all influence the earthquake vibration along the subway. The study reveals that with the increase of the incident frequency, the displacement of the ground surface becomes complicate gradually, and that there exist substantial differences between the isotropic site and layered site. Also, the stiffness and depth of the layer evidently influence the amplitude of displacement of the ground surface nearby, as well as the frequency spectra.Using the dynamic FEM the paper gives the scattering problem of the subway group to the earthquake waves in the layered half-space. The scattering of the elastic waves differs greatly between the double tunnels and single tunnel underground. The waves in the site of double tunnels, as well as the displacement of the ground surface, become even complicate due to the interaction between each tunnel. When the ratio of the tunnel distance to the incident wave length is greater than 20, the interaction between tunnels can be ignored and the calculation is identical to the single tunnel. The scattering of earthquake waves to the double tunnels underground differs greatly between single-layered bedrock and isotropic half-space.On the basis of the ground motion analysis, the model of subway tunnel and structures above is established. The wave problem in the half-infinite domain can be solved accurately and effectively by using finite element and viscoelastic artificial boundary. By the analysis of the parameters in detail, the paper studies the earthquake reaction characters of the of buildings of different height to some influencing factors such as the subway depth, the subway distance, the property of layer. The paper discusses the key factors and their acting mechanics and evaluates reasonably and analyzes quantitatively the influence of the earthquake reaction of the structure along the existing subways. The study reveals that the subways in the soft soil layer evidently influences the earthquake response of structures nearby,moreover,the lower buildings may be influend more seriously by the tunnels.