A numerical study on effect of underground cavities on seismic ground response due to Rayleigh wave propagation

Recent studies found that some structural damage can be attributed to the effect of surface waves. A shallow underground structure may be heavily influenced by surface waves, which makes to lose energy over distance more slowly than body waves. This study deals with evaluating the effect of Rayleigh waves (R-waves) interaction with underground cavities on the seismic ground response and amplification pattern using the Finite Element Method (FEM). First, the FEM model was verified to ensure its accuracy. Then, the influences of the effective parameters, such as cavity burial depth, distance from the cavity axis, and dimensionless incident frequency were investigated. Parametric studies revealed that the amplitude of ground motion is greater in the presence of a cavity with respect to that in the free-field condition. It was indicated that shallow cavities cause more amplification than cases with a larger depth ratio. By moving away from the wave source, the response of receiver points has a declining trend. Due to the complex interaction of R-waves with a cavity, the right side of the cavity has less amplitude than the left side. Finally, by increasing the dimensionless incident frequency, the distribution of the surface displacements and wave diffraction patterns gradually becomes more complicated while the peak displacement components decrease. Consequently, in light of the importance of the R-wave interaction with subsurface spaces, the findings of this study can help improve seismic design procedures and seismic microzonation guidelines.