层状场地脉动卓越频率对应的理论计算深度研究*

地脉动观测是一种简便有效的场地土层动力特性测试方法。本文依据场地脉动能量中瑞利波为主的特性,基于层状场地瑞利波弥散特征曲线,研究了不同场地条件下脉动卓越频率对应的瑞利波波长与场地自振频率理论计算深度之间的关系。计算结果表明：场地一定深度范围内土层剪切波速差异特性是其主要影响因素。如果土层波速差别较小或者某一波速占主导地位,则理论计算深度与瑞利波波长比值约为1/4a(a为瑞利波波速与剪切波速之比),与均匀场地结果接近；反之,土层波速差异越大,两者比值与1/4a偏离越远,且1/4a为比值上限。

Theoretical calculation depth corresponding to microtremors predominant frequency of layered soils

Microtremors observing is a kind of convenient and effective test method for site soils dynamic characteristics. According to the character of Rayleigh wave is the main energy in microtremors of sites and based on the Rayleigh wave dispersion curve of layered soils, the relationship between Rayleigh wave length and theoretical calculation depth corresponding to microtremors predominant frequency is analyzed. Computation results show that, the difference characteristics of soil layers shear wave velocity of site are the main influencing factor. If the difference of shear wave velocities is small or a certain wave velocity is dominant, then the ratio of theoretical calculation depth to Rayleigh wave length is about 1/4a ( a is the ratio of Rayleigh wave length to shear wave length). That is, is close to the result of uniform site. Conversely, the bigger difference of soil layers wave velocities, the further away to the ratio of 1/4a, and 1/4a is the upper limit.