Partially Embedded Periodic Barrier For Surface Waves In Soil With A Covered Layer

Periodic structures have bandgap characteristics so that vibrations or waves in the bandgap frequency range cannot propagate in the structure.Using the bandgap characteristics to design and analyze isolation structures has great theoretical and practical value.In this paper,a one-dimensional periodic partially embedded surface wave barrier with I-shaped cross section is proposed for the isolation of generalized Rayleigh wave and Love wave of far-field seismic surface waves in soil covered with a layer.The dispersion relation and frequency response of the wave barrier in the half-space covered with a layer are numerically simulated by using the finite element method(COMSOL MULTIPHYSICS 5.2a),the influence of the covered layer thickness and the embedded depth of the barrier at different sites are discussed.The differences of barrier isolation between the half-space covered with a layer and the homogeneous half-space are compared.The influences of the depth of the barrier,the geometric parameters and the soil parameters on the mid-gap frequency and bandgap width are discussed in detail in the case of type-I site with thin covered layer thickness.The isolation effect of wave barrier is studied in the case of both Rayleigh wave and Love wave.The shielding effect of wave barrier on Oroville seismic wave is simulated numerically.The conclusions are shown below:1.In most cases,the isolation frequency range of the barrier in half-space covered with a layer is smaller than that of the barrier in homogeneous half-space at type-I site and type-II site,so simplifying the half-space covered with a layer to homogeneous half-space can not achieve the expected isolation effect.The impact is not significant at type-III site and type-IV site,and when the thickness of the layer below the embedding depth reaches ten times the wavelength,the half-space covered with a layer can be simplified to a homogeneous half-space.2.The wave barrier designed in this paper has good shielding effect on Rayleigh wave and Love wave below 40 Hz,and it can isolate Rayleigh wave in plane and Love wave out of the plane simultaneously in a certain frequency range.3.Different site types and the depth of the barrier have great influence on the bandgap.In the case of type-I site,for Rayleigh wave,the deeper the depth of the barrier is,the higher the isolation frequency is,and when the thickness of the layer is large,the larger(smaller)the embedding depth,the larger(smaller)the total isolation frequency range below 40 Hz.However,the low frequency range(below 20Hz)will be reduced if the depth of embedding is too large or too small.The love wave is the opposite.When the thickness of the layer is large(small),increasing(decreasing)the depth of embedding is helpful to obtain a wide frequency range of low-frequency isolation(below 20Hz).A larger isolation frequency range can be obtained when the slab height is larger than the thickness of the layer and the barrier is fully embedded at type-II site.The depth of embedding determines the bandgap at type-III and type-IV sites.For low frequency band gap below 10 Hz,the depth of embedment should be about 1/3 of the plate height.At this point,the Love wave is similar to the Rayleigh wave.4.The thickness of the lower part of the I-shaped plate and the height of the upper part as well as the lower part of the I-shaped plate are key geometric parameters to the band gap,the frequency range can be widened by increasing the thickness of the lower part or decreasing the height of the upper part.5.The surface wave barrier designed in this paper has good shielding effect on Oroville seismic wave in soil covered with a layer.