Study On Dynamic Properties Of Silt With Different Fines Content Under Long-term Cyclic Loading

Since the nineteen seventies,scholars at home and abroad had begun to study the dynamic characteristics of silt under long-term cyclic loading,but before that,it was more focused on the sand than the study of silt.In recent decades,more and more scholars had studied on the dynamic characteristics of silt,investigated the influence of the factors such as fine particle content,drainage condition,consolidation ratio,confining pressure and so on.With the rapid development of the transportation industry,the study on dynamic characteristics of silt under long-term cyclic loading had been gradually carried out.In this paper,through dynamic triaxial test on typical silt conducted in xiasha Hangzhou metro by using dynamic triaxial apparatus(GDS)what with the servo motor.It analysed the dynamic properties of saturated silty soil under the condition of undrained and long-term cyclic loading with the different clay contents(7%?8%?10%?12%?14%)and different dynamic loads.On this basis,took a comparison on the dynamic characteristics when drainage conditions was changed.The content of this study was as follows:(1)Under the condition of different drainage(undrained and fully drained),controlled the clay content of silt specimen and dynamic amplitude to get dynamic strain,critical dynamic stress and volumetric strain,studied the influence of drainage conditions for dynamic strain of clay with different fines content under long-term cyclic loading.(2)Under the condition of undrained,controlled the clay content of silt specimen and dynamic amplitude to get the corresponding dynamic pore pressure and the critical dynamic stress.(3)Using numerical simulation software,analysised the cumulative strain and pore pressure of this kind of silt under long-term cyclic loading and provide the fitting parameters of these models.By means of long-term cyclic triaxial test of saturated silt with different fines content under different drainage condition,some important conclusions were obtained:(1)Saturated silt with different fines content was tested under long-term cycling loading,it's cumulative dynamic strain curve,dynamic pore pressure curve and volumetric strain curve were similar to law: these three kinds of curve values were increased with the increasing time;under same time,the larger the dynamic stress was,the lager the curve value was.Under the condition of undrained,dynamic strain curve and dynamic pore pressure curve could be classified as three basic types: stable profile,constructive profile and destructive profile.(2)Clay content influenced the dynamic stress and volumetric strain when it was 7% ~ 14%.The dynamic stress and volumetric strain firstly increased and then decreased with increased clay content,about 10% content of clay was a turning point.The law was same as dynamic strength law of this silt.(3)The drainage process strengthened the normally consolidated silt.Under the different drainage condition,the mechanism of cumulative dynamic strain was different.When the cyclic dynamic amplitude was small,the accumulated strain value created by drainage condition was greater than the undrained conditions while conclusion runed counter when the cyclic dynamic amplitude was big.Cumulative strain curve tended to be stable after the volumetric strain curve showed a stable situation.(4)Because the curves' form under R?R' condition and R?R' condition were different,the data processing needed to be processed in segment.According to the critical dynamic stress R',curves under R?R' condition used the improved zhang Jianmin model to fit while curve under R?R' condition used semilog model to fit.The coefficient of study was suitable proved that the model was ideal.Then,organized the coefficient through analyzing the fitting data and obtained main factor: drainage conditions,dynamic stress ratio and the content of clay what influenced the cumulative strain and pore pressure of this kind of silt what under long-term cyclic loading.