南京及邻近地区新近沉积土的动剪切模量和阻尼比的试验研究

通过对南京及其邻近地区河漫滩相成因的粘土、粉质粘土、淤泥质粉质粘土、粉质粘土与粉砂互层土、粉土、粉细砂等6类新近沉积土的自振柱试验，详细地探讨了围压大小、剪应变水平、土的颗粒组成和结构性对这6类新近沉积土的剪切模量G及阻尼比λ的影响。通过与Seed和Idriss建议的砂土G／Gmax-γ和λ-γ曲线变化范围的对比，结果表明，不能将粉质粘土与粉砂互层土简单地当作砂土或粉质粘土对待。通过试验和理论分析，给出了南京及其邻近地区6类新近沉积土动剪切模量和阻尼比随剪应变变化的平均曲线的拟合曲线、包络线及其参数的推荐值，对实际工程具有一定的借鉴作用。

TESTING STUDY ON RATIO OF DYNAMIC SHEAR MODULI AND RATIO OF DAMPING FOR RECENTLY DEPOSITED SOILS IN NANJING AND ITS NEIGHBORING AREAS

Through analyzing the test results of free vibration column apparatus on recently deposited soils of flood plain including clay,silty clay,mucky silty clay,silty clay and fine sand interbedded strata,silt and fine sand in Nanjing and its neighboring areas,the effect of confining pressure,shear strain and soil structure property on dynamic shear modulus G and damping ratio l is investigated in detail. The confining pressure has a significant influence on the dynamic shear modulus ratio. The more the effective confining pressure increases,the less the dynamic shear modulus ratio G/Gmax reduces with shear strain increasing. After normalized by Gmax,the values G/Gmax of different confining pressure scatter in a narrow band and their discreteness is small. Compared with the test results of Seed and Idriss for silty clay and fine sand interbedded strata,the value of shear modulus ratio changes between lower boundary of sand and saturated clay curve proposed by Seed and Idriss. Those values are close to lower boundary of sand and keep away from Seed-Idriss saturated clay curve,so it may be concluded that the dynamic shear modulus of silty clay and fine sand interbedded strata is similar to that of sand. For sand soil and silty sand including mucky silty clay,the value of damping ratio approaches the lower boundary of sand l-g curve proposed by Seed and Idriss. Damping ratio is smaller than that of sand soil when the shear strain is the same. However,for silty clay and fine sand interbedded strata,the date of damping ratio falls between upper boundary of sand and Seed-Idriss mean curve. So,the damping ratio of silty clay and fine sand interbedded strata is higher than that of general sand. By comparison between the test results and the variation range of G/Gmax-g and l-g curves of sand recommended by Seed and Idriss,it is concluded that the silty clay and fine sand interbedded strata should not be simply treated as sandy soil or silty clay. Based on the test results and theoretical analysis,the average curves,recommended values and envelopes of dynamic shear modulus ratio G/Gmax and damping ratio l versus dynamic strain g for recently deposited soils in Nanjing and its neighboring areas are presented. But the proposed values can only be used as reference because of the complexity of l and. G