Research On The Bearing Capacity Of Precast Piles Inserted Into Holes Under Complex Strat

The traditional precast pile design theory and construction method are mainly applicable to general geological conditions.Precast piles can cause problems such as adjacent pile floating,difficulty in penetrating medium coarse sand formations and difficulty in reaching the design depth,which are greatly limited in the application of complex geological conditions.Pilot hole implantation precast pile is a proposed construction method for these problems.In this paper,the bearing characteristics of precast piles implanted in pilot holes under complex formation conditions and pile-soil interface shear characteristics are studied by indoor model test and numerical simulation analysis.The research results of this paper can reveal the load transfer law and pile-soil action performance of precast piles implanted in complex formation pilot holes,and provide a theoretical basis for the design and optimization of this pile type.The main research work and research results of this paper are as follows:(1)A direct shear test was carried out on the contact surface between sand,silty,and Concrete test block by using a strain-controlled direct shear apparatus,and the effects of soil dry density,water content,and normal stress on the shear mechanical properties of the pile-soil interface were analyzed.The variation of the pile-soil interface shear displacement curve and the variation of interface cohesion,internal friction angle,and shear strength under different influencing factors were summarized.This provides a reference for further studying the mechanical properties of the interface between structures and soil in engineering.(2)An indoor model test of prefabricated piles implanted by drilling was designed and conducted.Including the design of the model test chamber,the composition of the loading system and the data acquisition system,and the manufacture of the model piles.Through the indoor model testing,the stress-settlement curve of the model pile under vertical load and the exertion characteristics of the side frictional resistance of the pile were studied.The differences in the pile foundation bearing characteristics between static pressure piles and prefabricated piles implanted by drilling under the same foundation environment were compared and analyzed.The test showed that the ultimate bearing capacity of prefabricated piles implanted by drilling under the same foundation environment was only slightly lower than that of static pressure piles,and it could meet the requirements of both bearing capacity design and construction requirements under complex geological conditions.(3)Based on the indoor model test,the finite element numerical calculation model was established,and the indoor model test was compared and verified and analyzed.By establishing a full-scale numerical calculation model of pilot hole implanted precast pile,the variable parameters of the model pile length,pile diameter,soil cohesion,internal friction angle,elastic modulus and friction coefficient of pile-soil interface around the pile were analyzed,and the influence degree of each influencing factor on the bearing performance of precast pile implanted in pilot hole under complex formation conditions and the variation law of load-settlement curve were studied.The study found that increasing the pile length and diameter and improving the mechanical properties of the soil around the pile can effectively increase the pile bearing capacity.In practical engineering applications,the selection of pile diameter and length should be flexible based on the actual engineering conditions,taking into account the pile bearing capacity design,allowable displacement,and economic factors.The mechanical properties of the soil around the pile can be improved through methods such as side-grouting.