循环荷载作用下重塑饱和粉黏土的刚度弱化特性研究

以东海大桥海上风电场项目为课题背景,通过动三轴系统对重塑饱和粉质黏土开展一系列长期不排水循环加载三轴试验,分别考虑围压、动应力比和频率3种因素,特别是对高频(f5 Hz)下土体的动力弱化特性进行了研究。试验结果表明:累积塑性应变与累积孔压随着循环次数的增加而增大并且趋于稳定,呈现出应变软化和孔压软化现象。割线动变形刚度模量和割线动弹性刚度模量则随着循环次数的增加,先急剧降低然后趋于稳定,从而表现出刚度弱化现象。进一步研究了割线动弹性刚度模量与循环应变幅值的关系,割线动弹性刚度模量的衰减趋势受动应力比和频率的影响不大,与围压有关,围压越大,割线动弹性刚度模量衰减趋势越慢,衰减稳定幅值越低。

The stiffness weakening characteristics of remolded saturated powder clay under cyclic loading

Based on the background of the Donghai Bridge offshore wind farm project, a series of long-term undrained cyclic loading triaxial tests were carried out on the reconstructed saturated silty clay through the dynamic triaxial system. Considering the confining pressure, dynamic stress ratio and frequency, the dynamic weakening characteristics of powder clay under high frequency (f>5 Hz) were studied. The results show that the cumulative plastic strain and cumulative pore pressure increase with the increase of thecycles and tend to be stable, which shows the strain softening and the pore pressure softening. The secant dynamic deformation modulus and the secant dynamic elastic stiffness modulus first decrease sharply with the increase of the cycles, and then become stabilized, which shows the weakening of stiffness. We further discusses the relationship between the secant dynamic elastic stiffness modulus and cyclic strain amplitude, and the dynamic stress ratio and the frequency has little influence on the attenuation trend of secant dynamic elastic stiffness modulus, but the confining pressure has great influence. The higher the confining pressure is, the more slowly the secant dynamic elastic stiffness modulus decay and the lower attenuation stable amplitude is.