Experimental Study Of Dynamic Characteristics And Microstructure Of Ningbo Soft Clay Under Cyclic Loading

In recent years,the rapid development of the infrastructure of roads,railways and urban rail transport,traffic speed,load and other substantial increase,so that people's lives become more convenient.But the traffic load is a long-term cyclic dynamic load,which will be long-term effect on the foundation soil and continue to influence.In the long run under the dynamic load caused by the settlement of soft soil foundation has become more and more prominent,often cause large deformation and instability of the disaster,causing great security risks.The dynamic characteristics of foundation soil is one of the key concerns of the people under long-term cyclic loading.This paper takes the typical silty clay in Ningbo area as the object,through the Geocomp dynamic shear test system studies on dynamic characteristics of silty clay in Ningbo.The influence of explores the influence factors of the vibration frequency,the consolidation pressure accumulative deformation of soil etc.The effects of vibration frequency,consolidation pressure and over consolidation ratio on the shear modulus and vertical stress of soil are studied.The microstructure characteristics of the sample before and after vibration were analyzed by scanning electron microscope SEM technique.There are some following main conclusions made from the experimental study:(1)Under a certain cyclic stress ratio,the cumulative deformation increases with the increase of the number of vibration.Under a certain condition,the cumulative deformation also increases with the increase of frequency.(2)The cumulative deformation of the sample will increase with the increase of the dynamic shear stress.With the increase of the consolidation pressure,the cumulative deformation curve becomes more and more steep,and the accumulated deformation is also more and more large.(3)The accumulative deformation is affected by the super consolidation ratio,and the cumulative deformation is smaller and smaller with the increase of the over consolidation ratio.(4)Shear modulus decreases with the increase of the vibration frequency,the larger the shear stress amplitude,the decrease rate of the shear modulus will be more and more.(5)When other conditions are the same,the greater the vibration frequency,the smaller the vertical stress.Under the same vibration times,with the increase of the amplitude of the dynamic shear stress,the vertical stress gradually decreases.(6)By using the technology of micro scanning electron microscopy SEM,obtained in undisturbed soil microstructure before and after cyclic shear test,through image processing software to get the microstructure of specimens under cyclic shear after gradually broken,scattered,small pore diameter increase.With the increase of over consolidation ratio OCR,the number of pores in the soil is decreased,the particles become more and more closely,the shear modulus increases,that is,the ability to resist deformation is enhanced.(7)Based on the previous models,the cumulative deformation models of two different curves are established,and the relevant model parameters are presented.