| The characteristics of pile-soil interface are one of the important factors affecting the bearing capacity of pile foundation.Due to the special properties of ultra-soft soil,the research on the mechanics and deformation behavior of the interface between ultrasoft soil and pile is of great theoretical and practical value.In order to reveal the shear strength and deformation characteristics of ultra-soft soil pile interface,this thesis uses conventional direct shear test equipment and self-developed multi-functional pile-soil interface shear test device,combined with La Vision analysis software,considering water content,pile standing time,pile material and other factors,the strength and deformation characteristics of ultra-soft soil-pile interface were studied,and the following conclusions were obtained :(1)With the increase of water content of ultra-soft soil,the internal friction angle and cohesion of the ultra-soft soil-pile interface will be significantly reduced,which will reduce the shear strength of the interface.When the water content of ultra-soft soil reaches 85 %,the stress level of the pile-soil interface is extremely low,and the shear strength is only 0.22 k Pa.(2)With the increase of pile standing time,the internal friction angle and cohesion of pile-soil interface increase.When the standing time increases from 3d to28 d,the shear strength of cement-soil-ultra-soft soil interface increases by 182 % at normal pressure of 50 k Pa.The cement mortar-ultra-soft soil interface increases when the normal stress is 50 k Pa,indicating that the characteristics of the ultra-soft soil-pile interface have obvious time effect.(3)The pile material has a significant effect on the shear characteristics of the pile-soil interface.The interface shear strength between super soft soil and cement mortar is greater than that between super soft soil and cement soil.(4)The water content and normal stress of ultra-soft soil have great influence on the thickness of shear zone at pile-soil interface.The increase of water content and normal stress of ultra-soft soil will increase the thickness of shear band.(5)The experimental results show that the tangential stiffness is a variable.With the advancement of the shear process,it shows a trend of increasing first and then decreasing,and gradually tends to a certain value.With the increase of water content of ultra-soft soil,the peak value and initial value of tangential stiffness decrease.When the normal pressure of the interface increases,the initial value and peak value of the tangential stiffness will increase,and the shear displacement will also increase when the peak value appears. |
