The Research Of The Horizontal Bearing Capacity Of Super-Long Pile Based On Meshless Natural Element Method

Numerical method is widely used in engineering as the development of science, inwhich the finite element has the widest applications. However, the finite element hasthe insufficiency of mesh distortion or tangles in dealing with issues of non-linearmechanics of large transformation and the problems of re-meshing and new errorsgenerated by the physical quantity conversion between the new and the old meshwhen solving issues of indefinite or movable boundaries as fluid vibration, crackpropagation, material phase change and forming, therefore the meshless method isapplied. Different from finite element method, the meshless method requires nodeinformation rather than unit or grid information, which can overcome theinconvenience and defects of applying the finite element method. In a variety ofmeshless methods, natural element method with its unique advantages obtained rapiddevelopment.Along with the large-scale construction of high-rise buildings, long-span bridgesand deepwater ports, super-long pile has been widely used to meet the requirements ofbearing capacity and displacement control of foundation. The working mechanismand force character of super-long piles are different from normal piles with a short ormedium length. But presently, as research of super-long pile in layered soil is stillrelatively backward, the method of design and calculation of super-long piles remainsin use of the theory of normal piles. The existing theory and analytical model are notcapable to fully consider characteristics of layered soil or the combined effect oflateral-vertical loads, as well as can not reflect the working properties of super-longpiles accurately.The following aspects have been researched on calculation method and bearingbehavior in this paper:1. In order to improve the computational efficiency of natural element method,the new interpolating function is constructed by edge elements of Voronoifigure which replaces body elements. The natural element method can overcome the inconvenience and defects of applying the finite element methodto deal with the large deformation problem. This method’s validity andrationale can be verified by calculating and analyzing the examples.2. According to the variation principle, this paper calculated the P-Δ effect ofsuper-long pile under the combined effects of lateral and axial loads, andobtained the modified element stiffness matrix. Faced with the largedeformation problem of super-long pile under the combined effects of lateraland axial loads, the nonlinear calculation method is established based on themeshless natural element method. The correctness and rationality of themethod can be verified by calculating and analyzing the example. Thecharacteristic of the P-Δ effect can be obtained. Because of the P-Δ effect, thereis a nonlinear relationship existed between the displacement response andexternal loads. The calculated results indicate that the P-Δ effect cannot beoverlooked where the soil of the foundation is relatively loose and where theunsupported length of pile is relatively large.3. According to the natural element method, this paper discussed the influencefactors of horizontal bearing capacity, including load value, loading sequence,length-diameter ratio, pile top restriction, horizontal load position, relativestiffness ratio of pile-soil and load distribution form.4. When utilizing the p-y curve to simulate the non-linear characteristics of soilsurrounding pile in layered foundations, due to having not taken into accountthe soil Mass’ longitudinal continuity, the calculation deviation of horizontaldisplacement increases with the growth of a load. This paper adopted thelayered elasticity system theory to consider the soil Mass’ longitudinalcontinuity, as well as utilizing the research method for layered isotropic bodies,assuming that the horizontal resistance is evenly distributed around theperimeter of the pile’s cross-section. then an appropriate transfer matrix methodof horizontal displacement coefficient for the soil surrounding pile in layeredfoundations was established. According to the calculation principle of finite element equivalent load, the horizontal displacement coefficient matrix wasdeduced as well as providing a corrected formula for the horizontaldisplacement of soil surrounding pile through the p-y curve method when theexternal load was increased. Following the established model a program wascreated which was used for calculating and analyzing the horizontaldisplacement coefficient matrix of three-layered soil in order to verify thismethod’s validity and rationale. Where there is a relatively large discrepancy inthe soil layers’ properties, this paper’s method is able to reflect the influence onthe layered soil’s actual distributional difference as well as the nearby soillayers’ interaction.