Study On Pile Negative Friction Caused By Soft Soil Seismic Settlement

The negative friction of pile foundation caused by seismic settlement of soft soil can cause serious foundation damage,which has been proved by many earthquake examples.However,due to the complexity of tests and calculations of pile-soil interaction under dynamic load,the researches are still in early stages.The generation mechanism of negative friction is not clear that can not be well prevented and controlled in engineering practice.On the basis of the existing research results,the negative friction of pile foundation caused by seismic settlement of soft soil is studied by using the method of static and dynamics laboratory test,shaking table test and finite element numerical simulation.The main research contents and results of this paper includes:1.Shaking table test of negative friction of single pile in soft soil field were designed and carried out.The macroscopic failure phenomenon of soft soil site was observed.According to the measured results of site acceleration,pore pressure,settlement and pile strain,the seismic response of soft soil,distribution and development of pile foundation negative friction and the position of the neutral point under horizontal and vertical ground motion loading were explored.On this basis,the physical and mechanical parameter tests and dynamic triaxial tests were carried out on the soft soil samples,The basic physical index,the shear strength,the relation curve of dynamic modulus ratio damping ratio with shear strain and the development law of residual deformation of soft soil were measured and analyzed2.Based on OpenSees finite element calculation platform,PIMY material and fluid-solid coupling element were adopted to simulate soft soil and elastic-beamelement to simulate pile.The method of pile-soil connection in the model was improved.Zero-length element and elastic-Perfectly Plastic material were used as the pile-soil contact surface.The influence of the gravity stress on the contact surface parameters is considered.A program for calculating the negative friction of single pile in soft soil was developed,which can take the pile diameter effect and the shear slip characteristics between piles and soil into account.3.Using the above numerical calculation program,Five ground motions with different characteristics in PGA,spectrum,energy(Arias intensity)and effective duration time were selected as input.The peak acceleration amplification coefficient,the acceleration response spectrum and the seismic amplification coefficient of the pile were studied.And the development and distribution characteristics of the negative friction resistance of soft soil pile foundation,the influence of ground motion parameters,pile diameter and other factors on the final value,growth rate and neutral point position of pile negative friction.4.Based on the results of experiment and numerical simulation,the generation process and disaster-causing mechanism of negative friction of pile foundation in soft soil site under the action of strong earthquake were discussed.The direction of future research and some related problems were pointed out.