Numerical Simulation Of Small Dimensions Steady State Rayleigh Wave Method

Rayleigh wave method has been widely used in the field of geological exploration and engineering test.Although it is also widely used in the empirical investigation of inhomogeneous geological in practice,the application of Rayleigh wave method to detect interface has not been clearly defined in horizontal layered medium and inclined interface layered medium.It is of great significance for improving the precision and expanding application of Rayleigh wave method through studying the effect of detecting interface in layered medium.It can be provided a new idea for studying this issue by performing the small dimension Steady-state Rayleigh wave test in a simple and easily prepared site model.It could make up for inadequate test samples which are caused by test equipment,test environment,test time etc.in the field test by using numerical simulation method.To analysis and compare the results of field test and numerical simulation are better to sum up the relevant characteristics and laws.In this paper,the small dimension Steady-state Rayleigh wave test in different sites are simulated by using spectral element analysis software Specfem2 D.Studies are focused on the feasibility of detecting interface in horizontal layered medium or inclined interface layered medium by using Steady-state Rayleigh wave method.The main research works in this thesis are listed as follows:1.The numerical simulation of small dimension Steady-state Rayleigh wave tests for homogeneous sand and concrete medium are conducted by using Specfem2 D software.The criteria of model size,mesh size and time step are discussed.The feasibility and accuracy of numerical simulation are verified by the comparison between the numerical solution and theoretical solution.Studies on the effects of offset and spacing provide reference for the small dimension Steady-state Rayleigh waves test.2.The small dimension Steady-state Rayleigh wave method test in horizontal double-layered medium is simulated.By comparing the results of field test,theoretical analysis and numerical simulation,the effect of phase difference,dispersion curve and spacing at low or high frequencies could be analyzed.We also discuss the relationship between the Rayleigh wave wavelength of dispersion curve's first ‘inflection point' and the interface depth.The results point out that the disadvantage of detecting interface by reducing frequency and increasing spacing in traditional test.3.The tests of small dimensions Steady-state Rayleigh wave method in inclined double-layered medium are described.The characteristic of phase difference spectrum which of different test direction,vibration direction and spacing have been analyzed in detail,especially numerical simulation of in the case of spacing is 0.5 m.The analysis has shown that the test on cross section perpendicular is equaled to test in horizontal layered medium,whereas the tests along the direction inclined interface in the direction are different from the shallow source excitation and deep source excitation,and the phase difference of deep source excitation is always greater than that of shallow source excitation.According to the depth of the source excitation,we can determine whether or not the interface is inclined,and the larger phase velocity site corresponds to a thinner first layer.