深海超软土动剪切模量与阻尼比特性研究

Dynamic shear modulus and damping ratio of deep-sea ultra-soft soil

海底表层的结构物在使用中可能受到动荷载作用,为保证其的长期稳定性,有必要对海床表层的深海超软土动力学特性展开研究。使用Anton Paar MCR302流变仪,采用应变控制模式,对含水率高于液限的深海超软土进行动态剪切测试,研究动态流变参数、动剪切模量G和阻尼比λ的变化规律。结果表明,随着剪切应变的增大,深海超软土的变形由可恢复的弹性变形主导逐渐过渡为不可恢复的黏性变形主导。通过建立动态流变参数与动剪切模量G和阻尼比λ的关系,探讨了深海超软土的动力特性。根据深海超软土动剪切模量G的变化特征,提出了峰值参考应变的概念,建立了最大动剪模量G_(max)与归一化含水率w/w_(p)(w为含水率,w_(p)为塑性含水率)的关系。结果还显示,相较于常规黏土,深海超软土的G/G_(max-γ)(γ为剪切应变)曲线衰减较快,且受塑性指数影响较小。深海超软土的阻尼比整体偏高,并随剪切应变的增大快速上升。根据试验结果,给出描述深海超软土G/G_(max-γ)、λ-γ曲线的数学模型。

Seabed surface structures may be subjected to dynamic loads.In order to ensure the long-term stability of them,it is crucial to study the dynamic characteristics of deep-sea ultra-soft soil at seabed surface.Oscillatory shear tests were carried out on deep-sea ultra-soft soil with water content beyond liquid limit by an Anton Paar MCR302 rheometer with strain control mode.The variations of dynamic rheological parameters,dynamic shear modulus G and damping ratio λ were studied.The test results showed that with the increase of shear strain,the deformation of deep-sea ultra-soft soil was dominated by recoverable elastic deformation and gradually transited to unrecoverable viscous deformation.By establishing the relationship between dynamic rheological parameters and dynamic shear modulus G and damping ratio λ,the dynamic characteristics of deep-sea ultra-soft soil were discussed.According to the features of dynamic shear modulus G of deep-sea ultra-soft soil,the concept of peak reference strain was proposed,and the relationship between maximum dynamic shear modulus Gmax and normalized water content w/w_(p)(w is the moisture content,w_(p) is plastic moisture content)was established.Compared with conventional clay,the G/G_(max-γ)(γ is shear strain)curve of deep-sea ultra-soft soil decreased faster and was less affected by plasticity index.The damping ratio of deep-sea ultra-soft soil was generally high,and increased rapidly with the increase of shear strain.Based on the experimental results,models suitable for describing G/G_(max-γ) and λ-γ curves of deep-sea ultra-soft soil were proposed.