Research On Uplift Bearing Characteristics And Calculation Method Of Pile Foundation Based On Piezocone Penetration Testing

Uplift pile is one of the measures which are often used in geotechnical engineering to increase the uplift capacity of structure.In a large number of engineering cases,uplift pile has been widely used.However,the research on the bearing characteristics and working mechanism of uplift piles lags behind the development of engineering,and a relatively fast and convenient method for evaluating the bearing characteristics of uplift piles is urgently needed.CPTU has been widely used in soil classification,in-situ consolidation and permeability characteristics.The application of CPTU of the prediction of pile bearing characteristics has a history of decades.Compared with other means such as uplift static load test,CPTU test has the advantages of rapidity.In this paper,Southeast University’s independent research and development method called SEU@CPTU-1 is used.In addition,the relationship between the CPTU parameters and the bearing characteristics of uplift pile is deeply studied.Combined with theoretical analysis,numerical simulation and other means,the mechanism of uplift pile in the working process and the pile-soil interaction mechanism are studied This paper presents an innovative method to predict the bearing characteristics of uplift piles based on CPTU,which is verified and analyzed by a project site in Wenzhou.The main contents of this paper are as follows:(1)The existing research results are summarized,and the relationship between CPTU test data and uplift bearing characteristics of pile foundation is analyzed.The results show that the increase of pile length,pile diameter and pile surface roughness will improve the uplift bearing capacity of the pile,and the change of pile-soil contact area will affect the failure mode of the surrounding soil.The distribution pattern of pile side friction is "first increase and then decrease",which is affected by the distribution of groundwater and the type of soil around the pile.(2)The deformation and stress of pile under uplift load are analyzed by ABAQUS finite element analysis software.The results show that in the process of bearing uplift load,the uplift displacement of the pile body relative to the soil is caused by tensile action,and the axial force and deformation of the pile body gradually decrease with the depth.Therefore,the upper part of the pile body bears most of the uplift load at the initial stage of the uplift load;When the load increases,the axial force and deformation of the middle and lower part of the pile body gradually develop;In addition,in the whole process of load application,the axial force transferred to the pile end is small.(3)Based on the model test and CPTU test,a calculation method for the uplift bearing characteristics of pile foundation in marine clay is proposed.The typical method based on CPTU test is compared with the method proposed in this paper.The results show that the proposed method is applicable to predict the uplift bearing characteristics of pile foundation in clay.(4)Based on the pull-out static load test of pile foundation on site,the distribution law of side friction,ultimate bearing capacity of pile foundation and axial force distribution of pile body under various loads are obtained,which provides a reference for verifying the rationality of the method proposed in this paper.The comparison between the uplift static load test and the prediction results further verifies the reliability of the method based on CPTU to predict the uplift bearing characteristics of pile foundation.