Bearing Capacity Analysis And Experimental Study Of Single Pile Under V-T Combined Loading In Gibson Subsoil

Due to their advantages in high bearing capacity, small settlement, convenient constructions and adaptability in complex geological environments, pile foundations are widely used in engineering practice. For those pile foundations adopted in urban overpass, bridges over large rivers or ocean, offshore oil platform and wind turbine generator tower, besides the vertical loads V down from the superstructures, obvious torsinal load T are often caused at the pile top by non-uniform or eccentric horizontal forces, lateral impact, earthquake or other factors. Those conventional design methods can not consider this kind of interaction between the vertical load V and torsion T, making it difficult to accurately evaluate the bearing capacity of the pile shaft, sometimes even result in the insecurity of upper structures. In order to study this problem, based on available research results and funded by the National Natural Science Foundation of China(NO: 51378197), theoretical analysis and laboratory model loading tests were carried out in this paper to discuss the bearing capacity of single pile under the combined loading of vertical force V and torsion T in generalized Gibson sugbrade, of which main work and achievements are as follows:Firstly, to discuss the behavior of piles offloaded by pure vertical force V or torsion T, the elastic and ideal elastic-plastic constitutive models were used to simulate the pile shaft and the surrounding subsoil respectively. By treating he subsoil as the Gibson model with the non-coordination deformation along the pile-soil interface considered as well, the control equation of the pile shaft was first set up by the load transferring function and shear displacement method s. Then, boundary force and displacement conditions were introduced to deduce the solutions for the inner forces and deformation of the pile shaft under various bearing stages of subsoil, which were represented by the Bessel function. At the same time, calculation results by the obtained solutions were compared with those availabe research results to verify the feasibility of methods presentes in this paper.Secondly, based on the obtained solutions for pure vertical loaded piles and torsional piles, various stress stages of the subsoil(i.e., elastic?elastic, elastic?elastoplastic and elastoplastic?elastoplastic stages) and loading paths(V?T and T?V) were considered to derive the analytical solutions for inner forces and deformation of the pile shaft under combined loading of vertical force V and torsion T respectively. Furthermore, various combined values and loading paths of V and T were adopted to determine the bearing capacity of the pile shaft. Accordingly, a calculation program was worked out by the mathematical software Mathcad, through which the parameter analysis was finished to discuss the influencing rules by the aspect ratio(L/D), elasticity modulus ratio(?) of pile shaft to subsoil and the ratio of the constant coefficient of the subsoil shear modulus distribution function to that in the ultimate friction resistance distribution function(n) on the bearing capacity of pile shaft with the failure envelops plotted correspondingly as well.Finally, by using the loading device of sand box and self-made pulley blocks, indoor model loading tests of single pile under pure torsional load T and the combined loading of vertical force V and T were designed and carried out respectively. From the tests, load-deformation curves at the pile top, inner forces and deformation along the pile shaft, and the failure bearing capacity of the pile shaft were obtained in detail. Finally, a comparative analysis was performed to find out a good agreement between the theoretical calculation results and measured values.