Scattering Of SH Wave By Debonded Inclusions And Linings In The Covering Layer

In recent years,the utilization of underground space has been unprecedentedly increased with the development of economic,urban space and national defense.However,underground structures are not absolutely safe in earthquakes.This is because researches on the seismic performance of underground structures is much fewer than seismic research of above-ground structures.Therefore,it is necessary to make detailed analysis and research on the dynamic response of underground structures in complex geological conditions under the action of seismic waves.For decades,the study of seismic wave problems usually analyze the earth as an infinite homogeneous elastic half-space.It cannot be ignored that the layered medium model is more in line with the actual engineering geological conditions.However,due to the complexity of its boundary conditions,theoretical research is more difficult.In the research field of elastic wave scattering in composite formations,there are still many gaps that need to be filled.In this paper,basalt,granite,coal and other rocks are used as the main constituent materials of the stratum.They are combined with geology and elastic dynamics to construct two typical composite stratum models of "upper soft and lower hard" and "upper hard and lower soft".Next,C30 concrete and Q345 steel are used as materials for lining the tunnel.So,four models are used in this paper to study the scattering of debonded lining tunnels in composite stratum under the action of SH waves.Through the first model,the construction method of the scattered wave field in the composite formation and the processing method of the debonded boundary are established.The scattering of SH waves by debonded concrete or steel inclusions in the covering layer is studied.The scattering of SH waves by arc-shaped cracks in the composite rock layer is derived from this model.Which lays the foundation for the subsequent research on lining tunnels.When the lining tunnel is located in and under the covering layer,the second and third models are studied respectively for the influence of factors such as geological conditions,lining materials and lining thickness on the phenomenon of dynamic stress concentration.On the base of the first three models,model four analyzes the scattering phenomenon of SH waves by debonded tunnels in the covering layer.The research ideas can basically be summarized as follows.Firstly,the large-circle assumption method is used to replace the straight-line boundary of the half-space with the circular arc boundary.Secondly,the complex plane is introduced to construct the stratum,degummed inclusions,or degummed inclusions through the wave function expansion method and the coordinate translation method.The wave field expression in the form of Fourier-Bessel series satisfies the Helmholtz governing equation in the lining.After that,the corresponding series equations are established using the boundary conditions of the specific problem,and the equations are solved by Fourier transform and truncated finite terms.Finally,the method of error checking is introduced to obtain a solution that satisfies the engineering accuracy in the numerical calculation.After the analyzation of four models,it can be found that the combination of soil layer and scatterer parameters in the composite formation is more complicated than the half-space problem.The dynamic stress concentration factor of the scatterer is affected by factors such as the soil layer,the parameters of the scatterer,the frequency of the incident wave,and the range of debonding.The cover layer with less rigidity has more obvious amplifying effect on the dynamic stress concentration factor,while the cover layer with greater rigidity has a certain shielding effect on SH waves.When the scatterers in the cover layer with less rigidity have degumming,low frequency and intermediate frequency incident waves have a greater impact on the dynamic stress concentration factor.When the scatterers in the covering layer with greater rigidity have degumming,the high frequency incident waves have a greater impact on the dynamic stress concentration factor.The scatterers have a greater impact on the dynamic stress concentration factor.The dynamic stress concentration increased with decrease shear modulus.For linings of different materials,increasing the thickness of the lining has different effects on the dynamic stress concentration factor on the inner and outer walls of the lining.Increasing the thickness of the lining does not necessarily reduce the dynamic stress concentration.The project should be analyzed based on specific conditions,and differentiated strengthening measures should be taken for the inner and outer walls of the lining.