Research On The Method Of Determining The Bearing Capacity Of Cast-in-Place Piles Based On Model Test

Bearing capacity of cast-in-place pile is the basis of pile foundation design.Scale model test of pile foundation is an indispensable auxiliary research method.The application of similarity conditions in most pile foundation tests is rough,which fails to fully consider the similarity error caused by the test parameters not meeting the similarity ratio,and can not reflect the bearing capacity of prototype pile foundation well,which limits the role of scaled model tests in quantitative analysis to a certain extent.By means of laboratory test,theoretical analysis and numerical simulation,the similarity condition of bearing capacity of pile foundation is modified,the factors affecting the similarity error of bearing capacity of pile foundation model test and its action mechanism are clarified,and two methods to determine the bearing capacity of prototype pile by model test are put forward.The main results are as follows:（1）Based on the similarity theorem and dimensional harmony principle,the macroscopic similarity relation of cast-in-place pile foundation under vertical load is derived,and the derived similarity relation is verified by finite element model.The definition of similarity error is made clear,and the source of similarity error of bearing capacity is analyzed theoretically through similarity condition.（2）In-situ test and scale model test of pile foundation are carried out to cla rify the existence of similar error.Based on the beta method for calculating ulti mate bearing capacity and the macro similarity relation of pile foundation,the si milarity condition of ultimate bearing capacity of pile foundation is modified by considering the factors causing similarity error,and it is found that the modified similarity condition is related to soil cohesion and ultimate bearing capacity of s caled model test.（3）The finite element numerical simulation method is used for single factor tests which affect the similarity error of ultimate bearing capacity of bearing model pile and uplift model pile respectively.The sensitive single factor is screened out,and the influence mechanism of single factor change on the similarity error of ultimate bearing capacity is analyzed,and the error prediction formula is determined by normalization.2^k-p factorial test is explained,and the interaction with significant effect is screened out.Response surface methodology is used to analyze the influence mechanism of interaction factors on the similarity error of ultimate bearing capacity,and the error prediction formula is determined.The prediction method of similar error of bearing capacity of pile foundation in the process of bearing force is further given by full factor test.（4）The method of determining the bearing capacity of prototype pile by model test is put forward.The scale model experiments of bearing pile and uplift pile are introduced with the prototype pile as the target object.The scale model experiments of bearing pile and uplift pile are carried out.According to the modified similarity condition and the similarity error prediction method,the bearing capacity of the prototype pile is determined respectively,and the similarity error of the ultimate bearing capacity can be controlled to about 10%by the two prediction methods compared with the in-situ test results.It is considered that the proposed prediction method is feasible.The research results provide a new idea for determining the bearing capacity of cast-in-place pile foundation.