Design And Investigation Of Periodic Barriers With Cross-like Empty/Filled Trenches For Seismic Surface Waves

Seismic surface waves,with features of large amplitude,long propagation distance and low frequencies(under 20Hz in most cases),could cause great failures to structures.Periodic surface wave barrier is an effective isolation measure.With a special design and optimization of structural parameters,bandgaps in which elastic wave propagation is not allowed will cover most frequency domain of seismic waves,so that a better isolation effect could be reached.Design and investigation on periodic seismic surface wave barriers will bring out great values both theoretically and practically.In this work,periodic cross-like empty trenches and filled trenches distributed on a homogeneous semi-infinite soil substrate in a square lattice are designed and investigated to isolate the seismic surface waves.The numerical simulations by the finite element method for the surface wave barrier problems in three dimensional semi-infinite space are explored.Using COMSOL Multiphysics 4.3 finite element software,the numerical simulation was carried out on the Dispersion curves,frequency domain and time domain responses of surface wave barriers.The surface wave mode is identified by the Graphical Features Discriminant Method.The effects of structure parameters of wave barrier on the complete band gaps are discussed.Oroville and Taft seismic time-history responses are analyzed respectively.The results show that:1.The periodic cross-like empty trenches and filled trenches surface wave barriers exhibit better isolation performances for low-frequency seismic surface waves below 20Hz,and the frequency range of attenuation domain can reach about 10Hz.2.The length and depth of cross-like empty trenches are key design parameters of the wave barrier performance.The longer the length,the wider the complete band gap and the lower the bandgap mid frequency.The deeper the depth,the smaller the stiffness of the structure,the lower the characteristic frequency.When the depth of empty trenches reaches about 1.25 times the size of the period constant,the width of complete band gap is maximized and the effect of isolation is best.As long as the width of empty trenches is set within the range of 0.2-0.35 times the size of the period constant,the width of the complete band gap is always the widest.3.The filling height of the filled trenches has a great influence on isolation performance of the wave barrier.The greater the filling height of the solid material,the greater the structural rigidity and the higher the eigenfrequency.When the filling height of the concrete filled trenches is 2/5 times the size of the depth of empty trenches,the width of the complete band gap is maximized,and the effect of isolation is best,but the attenuation is not as great as the empty trenches.For the water-filled trenches barrier,the greater the filling height,the smaller the structural stiffness and the lower the characteristic frequency.Although the complete bandgap width of the cross-like barrier filled with water is not as large as the empty trenches,a new band gap is created in the low-frequency region,which is favorable to the isolation of surface waves below 10Hz.4.The periodic cross-like empty trenches surface wave barriers have a good isolation effect on the Oroville seismic surface wave.The maximum horizontal acceleration is reduced by 97%,and the maximum vertical acceleration is reduced by 96%.When filled with water,the wave barrier has a very good isolation effect on the Taft seismic surface wave.The maximum horizontal acceleration is reduced by 49%,and the maximum vertical acceleration is reduced by 35%.