动荷载下深圳前海软土变形及微结构特征研究

Study on deformation and microstructure characteristics of clay in Qianhai Shenzhen under dynamic loading

为探讨轨道交通动荷载作用下软土变形特征,对深圳前海地区软土进行动三轴试验,并对土样进行电镜扫描,借助多种结构参数从微观角度解释动三轴试验中土样的变形机理。结果表明:围压为100~150 kPa、频率为0.5~1.0 Hz时,临界动应力比为0.2~0.3,但围压为100 kPa、振动频率为0.5 Hz时,临界动应力比为0.15~0.20。低于临界循环应力比的情况下,轴向应变的发展速率随动应力比增加而呈指数增加,围压越小、振动频率越小,轴向应变发展速率越大。通过对微观结构参数进行分析,发现围压的增加使得颗粒更加紧凑,颗粒更多地是被压密;动应力比和频率的增加则会使得土体颗粒更易发生破碎,孔隙更容易被较小的颗粒充填。

In order to study the deformation characteristics of soft soil under traffic loading,dynamic triaxial tests were performed for clay sampled from Qianhai District in Shenzhen.After the dynamic triaxial test,samples were sliced and scanned by scanning electron microscope and the fractal theory was used to explain the deformation mechanism.The test results showed that when confining pressure is 100~150 kPa and frequency is 0.5~1.0 Hz,the critical dynamic stress ratio will be 0.2~0.3;however when confining pressure is 100 kPa and frequency is 0.5 Hz,the critical dynamic stress ratio will be 0.15~0.20.When the cyclic stress ratio was lower than the critical value,the development rate of axial strain increases exponentially with increase of the dynamic stress ratio.The larger confining pressure and smaller vibration frequency were,the faster the axial strain developed.Through analysis of the microstructure parameters,it was found that the increase of confining pressure would make the particles more compacted,while the increase of cyclic stress ratio and frequency would make soil particles more fragile and the pore more easily filled by smaller particles.