南京新近沉积淤泥质土震陷特性试验研究

Experimental Study on Characteristics of Seismic Settlement of Recently Deposited Muddy Soil in Nanjing City

震陷是地基基础的主要震害之一。目前已建立了若干经验公式来估算土的永久应变势,但是已有的经验公式参数较多,需要做大量的试验才能确定这些参数。本文通过英国WFI振动三轴仪对南京新近沉积淤泥质土做了一系列的震陷试验,得到了不同围压、固结比和轴向动应力下的试验结果。分析发现,对不同围压和固结比,基于最大往返剪切作用面的概念,在双对数坐标系中轴向动应力与循环振动次数的关系可通过最大往返剪切作用面上的动剪应力比实现归一化,即仅做一个围压和固结比的试验即可得到土的全部震陷参数;结合前人提出的永久应变势经验公式,推出计算南京新近沉积淤泥质土的简化经验公式,其结果能较好地模拟土的震陷特性,在永久应变达到4%时,该土的永久应变急剧增长。

Seismic settlement is one of main earthquake disasters of ground base.So far some experiential formulas have been established to estimate the permanent strain of soil,but the number of parameters of these experiential formulas are too many.To determine these parameters,a lot of tests must be done.In this paper a series of seismic settlement tests of recently deposited muddy soil in Nanjing city were performed by WFI dynamic cyclic triaxial apparatus made in England.The permanent strain under different cell pressure,consolidation ratios and axial cyclic stress were acquired.It is found that the relationship of axial cyclic stress and number of cycles under different cell pressure and consolidation ratios could be normalized by shear stress ratio in the double logarithm reference frame based on the concept of maximum cyclic shear plane.That is all the parameters of seismic settlement can be determined by test under one cell pressure and consolidation ratio.The permanent strain formula established by Zhang Ke-xu and Chen Guo-xing could simulate the characteristics of seismic settlement of recently deposited muddy soil in Nanjing city.The permanent strain of the recently deposited muddy soil in Nanjing city increased suddenly when permanent strain is over 4%.