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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 non-resonant mode of Stokoe resonance column was used to apply the pre-torsional vibration to the dry sand sample. The influence of vibration history on the nonlinear dynamic characteristics of sand was systematically investigated. It is found that there is a threshold cycle number for a sand sample. Before this threshold value is reached, the maximum shear modulus of sand decreases with the number of cycles. The normalized shear modulus of sand is almost unaffected by the pre-load frequency, and the damping ratio increases with the pre-load frequency. The normalized shear modulus decreases as the number of cycles increases, while the damping ratio increases. Increasing the confining pressure will weaken the influence of the pre-vibration on the normalized modulus and the damping ratio, while reducing the confining pressure will further amplify the influence of the pre-vibration. The effect of vibration history on the normalized shear modulus and damping ratio is a common result of the wear action between the soil particles and the vertical reorientation of the particles.