地下洞穴对表面波表观相速度影响的数值分析

通过有限元数值模拟，得到了含洞穴固体介质在动荷载下表面质点的速度响应。根据表面质点响应中瑞利波和反射体波能量分配分析表观相速度扰动机制，讨论振源、测点、洞穴三者相对位置及频率对表面波表观相速度影响。表观相速度扰动程度随频率减小而增加，商至出现大扰动。大扰动峰值频率与反射波基频有关，基频随振源、测点及洞穴间相对位置变化。最后讨论由大扰动峰值波长与洞穴埋深关系，并给出洞穴埋深估算方法。

NUMERICAL ANALYSIS OF INFLUENCES OF UNDERGROUND CAVITY ON APPARENT PHASE VELOCITIES OF SURFACE WAVES

The surface particle velocity responses of a solid medium with a cavity under dynamic loads are numerically obtained by the finite element method. Mechanism of disturbance of apparent phase velocity is analyzed from distribution of energies of Rayleigh waves and the reflected body waves in the responses. Influences of frequency and relative distances among the source, receivers and cavity on apparent phase velocity of surface waves are discussed. Disturbance degree of the apparent phase velocity increases with decrease of frequency until a maximum one occurs. The frequency corresponding to the maximum disturbance is related to fundamental frequency of the reflected body waves. The fundamental frequency is varied with relative distances among the source, the receivers and cavity. The relationship between the depth of cavity below the surface and the wavelength corresponding to the maximum disturbance is discussed. The empirical method is suggested for the estimation of the depth of cavity.