Scale Effect Research On Load-bearing Characteristics Of Huge Size Foundation

Super-large diameter foundations(with a diameter up to 6-8m)are increasingly used in the bridge foundation and offshore wind farms.The scale effect has very complex impacts on the horizontal bearing properties of the foundations.For these large diameter pile foundation,the lateral bearing behavior is the key problem for the foundation design.Existing design methods are based on the small-diameter pile or in situ model test results,the engineering applications are generally based on results of small scale pile and directly apply to other diameter piles,due to the scale effect problem for large diameter base its calculation results are not reliable.The determination of bearing capacity and rational design of large diameter foundation is one key problem as the field test of large diameter foundation is difficult,and lack of similar experience,specific norms,clear norms and design methods.Therefore,depth research the horizontal bearing mechanism of large foundations,propose viable bearing capacity and deformation analysis method,to provide the necessary scientific basis for the bridge caisson base and offshore wind turbine foundation design,etc.,has important scientific significance and application value.This article relies on the National Key Basic Research and Development Program(973 Program,project number 2013CB036304)sub-project "Deep foundation bearing behavior under complex environment design evolution and long-term performance," to research the scale effect of steel pipe pile foundation and caisson foundation bearing characteristics.This paper aims to investigate the scale effect on earth resistance,additional bending moment and fatigue properties through theoretical analysis,laboratory experiments,numerical simulations and in situ tests.Based on numerical simulation,field validation and hyperbolic model,using the ABAQUS software to numerical analysis,proposed soil resistance correction formula based on the scale effect and soil parameters.The soil resistance correction formula was corrected the initial stiffness of p-y and ultimate soil resistance.Correction formula corrected based on the pile diameter,depth and internal friction angle and other factors,the p-y curve is very close to measured curve,it shows scale effect has greater impact on using p-y curve to research pile horizontal force characteristics.Winkler model was used in this paper to study the horizontal bearing characteristics of caisson foundation base considering the scale effect,and Euler-Bernoulli beam deflection linear differential equation was used to solve caisson deformation and internal forces.When the scale effect of caisson foundation is studied,in addition to considering the horizontal force,but taking into account the combined effects of friction of pile side and correction soil resistance,etc.formed a complete theoretical system to analyze horizontal bearing characteristics of caisson foundation combined with the transfer matrix method and Laplace inverse transform to achieve solving theoretical system,combined with the Huaihe River Bridge caisson situ horizontal load test(diameter of 5m,12m deep water)and Ma'anshan Yangtze River Bridge caisson(diameter of 6m,39m deep water)situ horizontal load test,situ test provided experimental verification for the study of the scale effect of caisson horizontal bearing characteristics.The results of two in-situ tests show that the calculated values are in good agreement with the measured values when considering the influence of lateral friction.The maximum error of displacement and bending moment is less than 10%,which indicates that the calculation theory can be very good in prediction of deformation and internal force characteristics of caisson foundation.This paper researched steel pipe pile bearing characteristics considering the scale effect.Based on the experimental data of 2m diameter steel pipe piles,the ABAQUS simulation parameters were calibrated to study the horizontal bearing characteristics of 6.6m diameter steel pipe pile foundation.Finally,the calculation theory was used to calculate the horizontal load.In addition to considering the horizontal force,but taking into account the combined effect of the pile body side friction and correction soil resistance,formed a complete theoretical system to analyze the horizontal bearing characteristics of steel pipe pile,combined with the transfer matrix method and Laplace inverse transform to achieve solving theoretical system.The solution process based on the actual stress situation of steel pipe pile,the pile into the free end,plastic section and the elastic section are solved respectively,and used results to build a complete solution system based on displacement compatibility and boundary conditions.The results of simulation results show that the calculated values are in good agreement with the simulation values.The maximum error of displacement and bending moment is less than 10%,which indicates that the calculation theory can be very good in prediction of deformation and internal force characteristics of large diameter steel pipe piles foundation.Finally,Relying on actual formation mechanical properties of Qiongzhou Strait Bridge project,the p-y curve and ?-s curves is calculated.Based on the calculation theory of giant foundation horizontal load-bearing characteristic,The horizontal force and deformation of a 88 m diameter caission under horizontal load is calculated,with a view to provide reference for engineering design and construction.