中文摘要：

循环加载条件下砂土的行为特性研究过去主要集中在松砂和中密砂方面。本文利用全自动三轴仪,对相对密度为80%的平潭砂进行了单调和循环荷载作用下的试验研究,分析了围压、固结侧压力系数、循环应力比对不排水条件下密砂超静孔压发展的影响规律。结果表明,固结侧压力系数和循环应力比共同影响土体的偏应力状态,它们对密砂的孔压发展有着决定性的作用。固结侧压力系数较大时,偏应力出现周期性的反向,超静孔压增长较快,砂土表现出典型的循环流动现象;而固结侧压力系数较小时,循环加载过程中偏应力始终在三轴压缩区内,产生的超静孔压较小,经过一定的周期数后,一个周期内由剪胀引起的超静孔压减小值正好等于由于剪缩所引起的超静孔压增大值,累积的超静孔压不再随周期数的增加而增大,密砂进入＂周期稳定状态＂,而在文献中关于松砂和中密砂的循环加载试验尚无存在该现象的报道。

英文摘要：

The past research on sand behavior under cyclic loadings mainly focused on the loose or medium-dense sand. By use of an automatic-controlled triaxial device, experimental study on the Pingtan sand with a relative den- sity of 80% was carried out, under both monotonic and cyclic loadings. Influences of the confining pressure, the lateral stress ratio at consolidation and the cyclic stress ratio on the development of excess pore pressure were ana- lyzed. It is shown that the lateral stress ratio at consolidation and the cyclic stress ratio, which determine the devia- toric stress state of the soil, exert a significant effect on the behavior of dense sand. The excess pore pressure in- creases relatively fast when the lateral stress ratio at consolidation is high and the deviatoric stress reverses periodi- cally, and the sand exhibits a typical response of cyclic mobility. The excess pore pressure induced by the cyclic loading is relatively low when the consolidation stress ratio is low and the deviatoric stress remains in the domain of triaxial compression. After a certain number of loading cycle, the positive and negative excess pore pressures gener- ated during a loading cycle neutralize each other, and the accumulated excess pore pressure does not increase with the number of loading cycle. The dense sand reaches a cyclic stable state. The phenomenon is not observed in the loose and medium-dense sand according to the literature.