表面波有效相速度近似分析方法

Approximate approach to analyzing effective velocity of surface waves

分层介质中瑞利面波有多个模态,表面瞬态响应是多个模态响应的叠加。在近场,面波模态响应传播速度随传播距离而变化;在远场,其趋于模态相速度。由分层介质表面两不同点响应互谱分析(SASW)得到的有效相速度并不对应于面波基阶模态相速度,它与波场中高阶模态能量分配比例有关。有效相速度随传播距离而变化,近场体波对有效相速度影响较大。对分层介质在简谐荷载下表面质点位移响应进行了互谱分析,得到了有效相速度理论值,通过理论值与测试值匹配分析可估算分层参数,该分析方法考虑了近场及高阶面波模态对有效相速度的影响。

The Rayleigh waves on layered systems are of multimode. The transient responses of the surface are comprised of ones of multimodes. In the near field where propagating distance is small relative to the wavelength, the propagating velocities of modal responses vary with the distance from the loading center, and approach to the phase velocities of modes in the far field. Affected by higher Rayleigh wave modes in the surface wave field, the effective phase velocity obtained by spectral analysis of surface waves （SASW） is not corresponding to the phase velocity of the fundamental mode. The effective phase velocity varies with the propagating distance. In the near field, the body waves have great influences on the effective phase velocity. The theoretical effective phase velocities can be got by spectral analysis of the discrete solution of surface displacement; the layer parameters can be evaluated by matching the measured phase velocity data with the theoretical ones. Influences of the near field as well as higher modes on the effective phase velocity are taken into consideration in this method.