振动历史对砂土非线性剪切模量和阻尼比的影响

Effects of vibration history on nonlinear shear modulus and damping ratio of sand

利用Stokoe共振柱的非共振模式对干砂试样施加先期扭剪振动,系统研究振动历史对砂土非线性动力特性的影响。研究发现:对某一砂样,存在一个阀值循环次数,小于该阀值前,砂土最大剪切模量随循环次数衰减,大于该阀值后,随之增大。砂土归一化剪切模量几乎不受预荷载频率影响,阻尼比随预荷载频率增大而增大。归一化剪切模量随循环次数增大而减小,阻尼比则随之增大。增大围压将减弱先期振动对归一化模量和阻尼比的影响,而降低围压将进一步放大先期振动的影响。振动历史对归一化剪切模量和阻尼比的影响是土颗粒之间磨损作用和颗粒竖向再定向作用的共同结果。

The effects of vibration history on nonlinear dynamic properties of dry sand are studied by applying torsional previbration using the non-resonant vibration mode by means of the Stokoe resonant column apparatus. The study shows that, for a given sand sample, there is a threshold number, below which Gmax decreases and beyond which it increases with the number of cycles. Norrn^lized shear modulus is not affected by preloading frequency but damping ratio increases with preloading frequency under the confining pressure under which previbration is applied. The normalized shear modulus decreases and the damping ratio increases with the number of cycles. Reloading confining pressure may decrease and unloading confining pressure may further magnify the effects of the vibration history on the normalized shear modulus and the damping ratio. The effects of vibration history on the normalized shear modulus and the damping properties result from for the jointed effects of wear process and reorientation of interparticles in vertical direction.