Research On Vertical Bearing Capacity Of Prestressed Pipe Pile In Strongly Weathered Based On In-situ Test

Prestressed pipe pile is a main pile type in pile foundation.Because of its stable and reliable quality,high concrete strength of pile shaft and high bearing capacity of single pile,it has been widely used in China.The existing methods to determine the vertical bearing capacity of prestressed pipe piles mainly include theoretical method,field test and laboratory test.However,the theoretical method has the problems of difficult to determine parameters and heavy calculation workload;The field test has the problems of long time and insufficient stimulation of pile end bearing capacity;Because of the size effect,the results of the laboratory test have a large error with the actual results.In view of this,this paper explores a calculation method based on in-situ test data,that is,the method of carrying capacity field test after pile completion is used to study and extract mechanical parameters,and build a foundation database;The vertical bearing capacity of prestressed pipe pile is calculated by using the mechanical parameters obtained from the database analysis,so that the calculated results are closer to the actual bearing capacity of the pile.This paper collects the in-situ test data of prestressed pipe pile in strongly weathered rock in the past 15 years in Chancheng District,and proposes a method for calculating the vertical bearing capacity of prestressed pipe pile based on the in-situ test data.The refined numerical calculation method of dynamic bearing capacity of foundation pile considering layered soil damping coefficient and elastic limit parameters is established.The test site was established to conduct high strain test,static load limit load test and sliding micrometer test on20 test piles in the strongly weathered argillaceous siltstone and strongly weathered mudstone bearing stratum,and the reasonable value range of mechanical parameters of each soil layer was studied.The influence of soil distribution on soil dynamic response under high strain hammer driving is analyzed by taking soil samples from the test site for dynamic triaxial tests.The main research contents are as follows:(1)The recommended value of the pile side friction correction coefficient related to the soil layer category and the depth of the soil layer is proposed.By collecting the strain dynamic testing and static loading test in-situ test data of about 1000 piles in the past,and extracting mechanical parameters such as pile side friction,pile tip resistance and pile tip displacement,the foundation database is constructed.The standard mechanical parameters of each type of soil layer are obtained by classification statistics method.The results show that the mechanical parameters of different types of soil with different buried depth based on in-situ test data are more reasonable,so the recommended value of the pile side friction correction coefficient related to the soil layer category and the depth of the soil layer is proposed.(2)A calculation method of vertical bearing capacity of prestressed pipe pile based on in-situ test data is proposed,and the static resistance model of pile tip soil is studied to provide theoretical basis for the establishment of static calculation model.In this method,the physical and mechanical parameters are obtained by field test after pile forming,and the mechanical parameters obtained by in-situ test data analysis are applied to the calculation method,and the corresponding static bearing capacity calculation program is compiled,so that the calculation results of pile bearing capacity are closer to the actual bearing capacity of pile.(3)The refined numerical calculation method of dynamic bearing capacity of foundation pile considering layered soil damping coefficient and elastic limit parameters is established.The numerical analysis method of dynamic test bearing capacity of original foundation pile is improved.The nonlinear distribution model is used to determine the pile side resistance,and different damping coefficient and elastic limit are used to determine the dynamic parameters of soil layer.It solves the problem that damping coefficient and elastic limit parameters of each soil layer can not be determined by layers in the traditional pile-soil mechanical model of dynamic bearing capacity of foundation pile.The corresponding calculation program of dynamic test bearing capacity is compiled to make the calculation results of pile bearing capacity more in line with the actual situation.(4)Two typical strongly weathered rock layers were selected as the bearing stratum at the pile end,and twenty prestressed pipe piles were tested by high strain dynamic testing,static load limit load test and sliding micrometer test.The mechanical parameters of the field test results are extracted for research,and the reasonable range of relevant mechanical parameters is proposed.Through field static and dynamic contrast test and sliding micrometer test,the influence of the soft and hard degree of the rock layer at the pile end and the penetration on the damping coefficient is revealed.By using sliding micrometer to test internal force,the pile side resistance,pile end resistance and pile end displacement can be obtained,which is conducive to the study of the bearing mechanism of prestressed pipe pile.(5)The physical and mechanical indexes of four typical soil layers around piles are tested by dynamic triaxial test,and the dynamic characteristics of soil around piles are studied.The influence of soil layer distribution on the dynamic response of soil under high strain hammering is analyzed.The results show that the dynamic deformation response of soil around the pile is obviously related to its buried depth.The soil layer distribution,especially the shallow soil layer distribution,has a great influence on the dynamic response of high strain hammering pile.The research on the vertical bearing capacity of prestressed pipe pile based on the in-situ test data adopts the method of field test after pile completion to study and extract the mechanical parameters.The obtained mechanical parameters and the corresponding pile side and pile end transfer function are closer to the actual situation,so that the calculation result of the vertical bearing capacity of pipe pile is closer to the actual bearing capacity of pile.Therefore,this research method has more advantages than other research methods,and has important reference value.