宁波近海沉积土动力特性的试验研究

Experimental study on dynamic characteristics of Ningbo's offshore sediment soils

土的动模量、阻尼比和砂土抗液化强度是土动力特性的主要指标,是研究重大工程场地设计地震动参数的基础性资料。结合宁波象山港大桥工程场地地震安全性评价工作,采用南京工业大学自行研制的GZZ-1型自振柱仪,首次对宁波近海沉积的淤泥质粘性土、粘性土和砂土进行了动模量和阻尼比的试验研究。发现土的动剪切模量比G/Gmax、阻尼比λ与剪应变幅值γ的关系,可分别采用Martin-Davidenkov模型和作者建议的阻尼比经验公式进行拟合;此外,采用南京工业大学自行研制的DSZ-1型动三轴仪,首次对宁波近海沉积的砂土和粉土进行了液化试验研究,结果表明,宁波近海沉积的砂土和粉土的抗液化强度可采用指数函数进行拟合,且与南京长江三桥场地粉土的抗液化强度相近,但明显大于福建标准砂的抗液化强度。

The dynamic shear modulus and damping ratio of soils are two principle indexes of soil dynamic characteristics, and are still the basic data of design ground motion parameter research for important project＇s site. In this paper, combining with the work of earthquake safety assessment of Xiangshan Port Bridge＇s site in Ningbo City, using the free vibration column test system developed by Nanjing University of Technology, the dynamic modulus and damping ratio tests for Ningbo＇s offshore sediment muddy clay, clay and sand soils are conducted for the first time. The results show that it is suitable to use Martin-Davidenkov model and the empirical damping ratio formula recommended by Chen Guo-xing to fit the relationship of the mean dynamic shear modulus ratio G/Gmax and damping ratio λ to amplitude of shear strain γ- In addition, using the cyclic triaxial test system developed by Nanjing University of Technology, the liquefaction tests of Ningbo＇s offshore sediment sand and silt soils are also conducted for the first time. And the result shows that the liquefaction resistance of Ningbo＇s offshore sediment sand and silt soils can be expressed by the empirical exponential function formula. Compared with the liquefaction resistance of the sand and silt at Nanjing＇s Third Bridge of Yangtse River and Fujian standard sand, the liquefaction resistance of Ningbo＇s offshore sediment sand and silt is closed to that of the silt at Nanjing＇s Third Bridge of Yangtse River, and it is obviously larger than that of Fujian standard sand.