Study On Numerical Computing For Equivalent Mechanical Parameters Of Soft Soil Foundation Treated By PHC Pile In Highway Of Dongting Lake Area

PHC piles which can effectively improve the bearing capacity of foundations are more and more widely used in China,especially for the treatment of soft soil foundation of highway.However,the interaction mechanism between PHC piles and soft soil is still complex and the theoretical research is not yet mature.Therefore,it is critical to raise and solve new problems in actual engineering,and to improve relevant theories constantly.In this study,combined with engineering cases,equivalent mechanical parameters of soft soil foundation treated by PHC piles in highway of Dongting Lake Area were investigated.The main contents of this study contain the following five aspects:1)The stiffness and strength parameters of different layers of soft soil foundation in the test section of actual engineering were obtained by indoor test.The settlement and displacement of the field test section were then monitored and analyzed.Test results show that the maximum settlement of soft soil foundation treated by PHC piles after the preload is about 246.3 mm,and its maximum horizontal displacement is about 25.2 mm,which is less than the safety control standard.Thus,the effectiveness of PHC piles used for the treatment of soft soil foundations was verified.2)An on-site simulated computing model was established using ABAQUS,and a complete set of methods for the computing of equivalent stiffness parameters of PHC pile-soil composite foundation were formed on the computer through a large number of model computing and analysis.At the same time,the stiffness parameters of the model of pile diameters and spacings corresponding to different pile lengths were also calculated.It is found that after the treatment of PHC piles,the elastic modulus of soft soil foundation increases and its Poisson’s ratio deceases,that is,the deformation resistance of soft soil foundation treated by PHC piles is effectively improved,and its main influencing factor is pile length.3)The strength parameters of PHC pile-soil composite foundation were calculated by triaxial numerical test.It is shown that the soil at the bottom of the pile is first damaged under the action of dimensional and axial pressures.With the increase of axial pressure,the damage extends along 45° in both directions,forming a "V"-shaped plastic zone.The damage degree of soil between the piles is much smaller than that of soil outside the piles,indicating that the strength of soft soil foundation treated by PHC piles can be effectively improved.4)An equivalent foundation model was established using ABAQUS.The corresponding settlement and displacement were calculated,and the field monitoring data was compared for error analysis.The results show that the settlement and displacement errors are between 15%20%.As a result,it is verified that equivalent mechanical parameters of PHC piles used for the treatment of soft soil foundation are effective,which can provide computing methods and logical ideas for other scholars.5)The test results were visually analyzed using the orthogonal test method to obtain the significance of the three influencing factors(pile length,diameter,and spacing),and the regression equation of these factors with equivalent mechanical parameters was fitted using SPSS software,which provided a theoretical basis for the preliminary design.