Bearing Behavior Of A Single Pile Under V-T Combined Loading By Theoretical And Numerical Analysis

Due to its advantages of small settlement,high bearing capacity,strong seismic perfermance and adaptability in complex geological environments,pile foundations are used widely in engineering practice.In recent years,with the rapid development of infrastructure construction,such as offshore oil platform,bridges over large rivers or ocean wind turbine generator tower,pile foundations especially large diameter single pile foundations have been chosen as an important foundation type.Because of the particular force environment in this kind of structures,the torsinal load T are often caused by eccentric horizontal loads including huge wave,hurricane and so on.For these pile foundations,besides the vertical load V,horizontal force H and moment M down from the superstructures,nonnegligible torsinal load T are often caused at the pile top.Those conventional design methods can not consider this kind of torque T,making it difficult to accurately evaluate the bearing capacity of the pile shaft,sometimes even result in the insecurity of upper structures.So reasonable design methods should consider the combined loading of V,H,M and T.Given the complexity of the problem and based on available research results,theoretical analysis and numerical simulation were carried out in this paper to discuss the bearing behavior of single pile under the combined loading of vertical force V and torsion T,of which main work and achievements are as follows:Firstly,to discuss the behavior of piles loaded by pure vertical force V or torsion T,the soil shear modulus profile is considered non-zero at the surface and follows a power function distribution with the depth.And the ideal elastic-plastic and elastic constitutive models were used to simulate the the surrounding subsoil and pile shaft respectively.The control equation of the pile shaft was first set up based on the pile displacement method and the load transferring function with the non-coordination deformation along the pile-soil interface considered as well.Then,force and displacement boundary conditions were introduced to deduce the analytical solutions of the pile shaft under various bearing stages of soil.At the same time,calculation results by the obtained solutions were compared with those availabe research results to verify the feasibility of methods presented in this paper.Secondly,based on the obtained solutions of pure torsional piles and vertically loaded piles,various loading sequences(V?T and T?V)were considered to derive the analytical solutions for internal forces and deformation of the pile shaft under combined loading of vertical force V and torsion T,from which the corresponding ultimate bearing capacity of the pile shaft were obtained.On this basis,a program to calculate the inner forces and deformation of pile shaft under combined V-T loading was worked out by MATHCAD.Then a parameter analysis was finished fo find out the influencing rules by the aspect ratio(L/D),the stiffness ratio(?)between pile shaft and subsoil and the constant ratio between the subsoil shear modulus and the ultimate friction resistance(n)on the bearing capacity of pile shaft,from which the failure envelops in various loading sequences were plotted as well.Finally,a 3D bearing capacity numerical analysis model of single pile foundations was established by ABAQUS and verified strictly.The stress and displacement contours of the pile and soil under different load conditions were obtained by comparative numerical simulation analysis.Then the bearing and deformation mechanism of the pile shaft under combined V-T loading were discussed in detail,and the main factors as well as corresponding influencing laws on the bearing capacity of single pile foundations were further investigated.