Experimental Study of Factors Affecting the Spectral-Analysis-of-Surface-WavesMethod

摘要

Three series of seismic tests were performed to investigate factors which affectthe Spectral-Analysis-of-Surface-Waves (SASW) test method. In the first series, the source of seismic waves was studied. Until recently, transient input motion has been used almost exclusively as the source with often unpredictable results. Random and sinusoidal input motions were investigated to evaluate if either could provide more consistent results. The investigation revealed that sinusoidal input attained substantially higher signal-to-noise ratios than either transient or random motions. The improved signal-to-noise ratio may be very helpful in situations where transient motion fails to provide acceptable results. A basic assumption of the SASW method is that only fundamental mode surface waves exist in the field. The assumption was investigated in the second series of tests using measurements of particle motion versus depth to calculate the relative contribution of the first several modes of surface wave propagation. Finally, the third series of surface wave tests was performed on a concrete test slab to assess the influence of the relative stiffness of adjacent layers and the relative spacing of source and receivers on measured dispersion. Results of the test series indicated that a large stiffness ratio between adjacent layers can adversely affect measured dispersion curves for wavelengths which are between approximately 0.7 and 1.8 times the thickness of the slab.