Research On Load Transfer Law And Accurate Conversion Of Bearing Capacity Of Self-anchored Test Pile

Pile foundation is the most widely used form of foundation in engineering construction.The premise of pile foundation application is to determine its pile bearing capacity through pile foundation testing.The commonly used pile foundation detection methods currently have many shortcomings,such as long detection time,single application scenario,and high cost.The self-anchored test pile method is a newly patented technology developed in recent years,which has many advantages such as wide application scenarios,simple operation,low cost,etc.At present,the self-anchored test pile method is in the stage of technology development and application,and the research content is mainly in the indoor model test and theoretical analysis,lacking relevant research on on-site tests.This paper conducts research on the load transfer law and accurate conversion of bearing capacity of self-anchored test piles through in-situ testing.In this test,the pile-end soilless compressive pile,uplift pile,the conventional compressive pile and the self-anchored test pile were taken as the research objects.Study on the load transfer law of self-anchored test pile by compiling and analyzing static load test data.For the practical application of self-anchored test piles,an accurate conversion method based on shear displacement method was proposed for self-anchored test pile.Finally,FLAC3 D finite difference software was used to simulate the in-situ test,and the numerical simulation data were compared with the measured results of the in-situ test.The main research content and conclusions of this paper are as follows:(1)By conducting static load tests on the test piles in the in-situ test,the bearing performance and load transfer law of four test piles under vertical compressive(pull-out)load were analyzed.The ultimate bearing capacity of each test pile was determined by combining the test pile load-displacement Curve and displacement-time logarithm Curve performance.Summarize the test pile load transfer law by analyzing the distribution curves of pile axial force and the skin friction.The analysis shows that the distribution curve of the skin friction of the upper section of the self-anchored test pile is similar to that of the uplift pile,showing the variation law of "large in the middle and small on both sides",The distribution curve of the skin friction of the lower section of the pile shows a positive trapezoidal distribution,with the maximum value of the skin friction gradually moves towards the bottom of the pile,and the increase amplitude gradually increases.(2)The positive and negative friction resistance conversion factor suitable for this test soil layer is 0.84,obtained from the static load test results and the skin friction distribution curves of the pile-end soilless compressive pile and uplift pile.At the same time,by comparing the test results of the pile-end soilless compressive pile and conventional,the skin friction distribution curves of the two test piles were normalized to analyze the evolution law of pile-side friction resistance.The results show that the soil at the pile end restricts the lateral dynamic resistance of the middle and lower part of the conventional compressive pile compared with the pile-end soilless compressive pile.This restriction manifests itself as a reduction in pile skin friction,and the weakening effect decreases from bottom to top.(3)This paper proposes an accurate conversion method based on the shear displacement method to convert the results of self-anchored test pile to the compressive results of single pile.First,the analytical axial forces and displacements at each section of the upper and lower sections of the pile are calculated under the action of the load,and the analytical results of the upper section are converted by using the lateral resistance hyperbolic transfer function to determine the loads at each level of the upper section,and then superimposed with the loads of the lower section to obtain the loads at each level after conversion.By superimposing the resolved displacements of the upper and lower sections of piles,the displacements corresponding to each level of loading are obtained.Finally,the load-displacement curve of the conventional static load test monopile was obtained after conversion.Compared with the static load test results of the compressive pile system,the ultimate bearing capacity error obtained by this method is 4.5%,and the ultimate displacement error is 6.8%.The ultimate bearing capacity of a single pile obtained by this method is biased towards safety and has certain practicality.(4)Using FLAC3 D numerical simulation software,numerical simulation calculations were conducted on the pile-end soilless compressive pile,uplift pile,conventional compression pile,and self-anchored test pile in in-situ test.The load displacement relationship,pile axial force distribution curve and pile lateral friction distribution curve from the numerical simulation were compared with the measured data from the in-situ test,and the two data were found to be a better match.