新近沉积土的动剪切模量和阻尼比试验研究

Experimental Study on Dynamic Shear Modulus and Damping Ratio of Recently Deposited Soils

江苏沿海地区由于特殊的地理位置优势以及经济的快速发展,港口码头、风力发电厂等重大工程不断新建。土的动剪切模量和阻尼比是重大工程进行抗震设计所必须的基础性数据。该地区的地层受晚更新世以来三次海侵的影响,普遍分布有厚度较大的海相地层。使用南京工业大学岩土工程研究所自行研制的GZZ-1型自振柱仪,结合重大工程建设,历时3年,对不区分陆、海相沉积的淤泥质土、粘土、粉质粘土、粉土、细砂等5类新近沉积土以及海相沉积的粉质粘土、粉土和细砂等3类新近沉积土共134个原状土样,进行了土的动剪切模量比和阻尼比的试验研究,结果表明:采用Martin-Davidenkov模型和陈国兴等建议的阻尼比经验公式拟合江苏沿海地区新近沉积土的动剪切模量比G/G_(max)和阻尼比λ与剪应变幅值γ_a的关系曲线是合适的,给出了各类土G/G_(max)～γ_a和λ～λ_a关系曲线经验公式的参数值;通过对比海、陆相沉积的粉质粘土、粉土和细砂等3类土的试验结果发现:海、陆相沉积的粉质粘土的动剪切模量比和阻尼比十分接近,而海、陆相沉积的粉土和细砂的动剪切模量比和阻尼比存在较大的差别。

Owing to the special geographic location and the rapid development of economy in coastal region of Jiangsu province, many important projects have been constructed such as digital strong ground motion observation stations, ports or wharfs, wind power stations. The dynamic shear modulus and damping ratio of site soils are basic and necessary data for the seismic design of important projects. Based on the construction of those important projects, experimental studies on dynamic shear modulus and damping ratio of 134 undisturbed soil samples are accomplished in about 3 years, using the free vibration column test system developed by Nanjing University of Technology. Those undisturbed soil samples are muddy soils, clay, silt clay, silt and fine sand. The marine deposited soils in coastal region of Jiangsu province are existed extensively due to three times of transgression after the late Pleistocene Epoch. Therefore, marine deposited silt clay, silt and fine sand are also screened. The results show that it is suitable to use Martin-Davidenkov model and the damping ratio empirical formula recommended by Chen Guoxing to fit the results of the normalized mean dynamic shear modulus ratio G/Gmax-γn and damping ratio λ -γn curves respectively. The reference values of regression coefficients are also given. By comparing the dynamic shear modulus ratio and damping ratio of marine deposited soils with continental deposited soils, the following results can be found ： for silt clay, the dynamic shear modulus ratio and damping ratio of marine and continental deposited soils are much dosed with each other, for silt and fine sand, however, the dynamic shear modulus ratios and damping ratios of marine and continental deposited soils are obviously different.