Research On Performance Behavior Of Batter Piles Foundation

Batter piles are used as foundation support for structures such as bridge abutments, docks, power transmission lines and offshore oil platforms. While batter piles have been used in some foundation projects, the analysis methods and theories for the behavior of batter piles lag for engineering applications. In view of this, the bearing mechanism of a batter pile under axial compressive loads, the working mechanism of a batter pile under the radial loads, performance behavior of a batter pile under inclined loads, the mechanical response of batter piles group under horizontal and vertical loads, and the dynamic response of batter piles group under seismic loads were analyzed by means of the methods of the theorical analysis, numerical simulation and model exeperiment. The main works and conclusions include that:(1) The calculating formula of axially bearing capacity and settlement for a batter pile was deduced based on the mechanism of pile-soil deformation compatibility, according to the non-uniform distribution property of the friction resistance around batter pile shaft. The calculated results show that the value of the pile axially bearing capacity and the settlement calculated by this paper’s formula decreases with the increasing in pile inclination. And considering different pile diameters, the value of the pile axially bearing capacity calculated by this paper’s formula is slightly smaller than the value calculated by the code’s formula and settlement calculated by the code’s formula is maller than the value calculated by paper’s formula. The lesser pile length of pile is, the smaller bearing capacity calculated by the code’s formula is than the values calculated by this paper’s formula, and with the increasing in the pile length, the value of bearing capacity calculated by this paper’s formula is greater than the value calculated by the code’s formula. The lesser utmost friction resistance of pile is. the smaller bearing capacity calculated by this paper’s formula is than the values calculated by the code’s formula, and with the increasing in the pile length, the value of bearing capacity calculated by the code’s formula is greater than the value calculated by this paper’s formula. For the same load, settlement calculated by the code’s formula is smaller than this paper’s formula.(2) Radial load monoclinic pile p-y curve considering influence of pile inclination established based on the large number of numerical simulations and the mechanical behaviors of batter pile was revealed. The calculated results show that the value of moment and displacement of batter pile calculated by this formula is smaller than the value of moment and displacement of batter pile calculated by the "m" method. And the moment and displacement of the batter pile decreases with the increasing in pile inclination.(3) Based on the elastic-plastic constitutive relation of non-associated flow Mohr-Coulomb criterion, a 3D elastic-plastic finite element model is built to analyze the influence of inclined angles of load and pile on the mechanical property of batter pile under inclined load. The result indicates that the stiffness of batter pile depends on both the axial and horizontal stiffness under a smaller inclined load, and the stiffness of batter pile does not develop the maximum under the axial force due to the existing stiffness balance in the axial and horizontal direction; The relationship between the ultimate compressive bearing capacity of batter pile and the load inclined angle presents a’M’shape, The peak of ultimate pile compressive bearing capacity appears near a small load angle of inclination instead of under axial load; Stiffness and bearing capacity of the batter pile increase with pile inclination under the positive inclined loads-while the result shows the opposite under negative inclined load; The ultimate loads of batter pile with different inclination are significantly affected by the coefficient of friction between the pile and soil.(4) The behavior of batter piles group under horizontal load or vertical load are analyzed based on three-dimensional elastic-plastic finite element method. The results indicate that the pile displacement and bending moment of the pile shaft of different pile inclination angles or different pile spaces are basically the same under horizontal load. When the inclination angle of plie is small, load sharing ratio of the front pile decreased and load sharing ratio of the row pile increases. When the inclination angle of plie increases, the load sharing ratio of the front pile and in the overall downward trend, but the load sharing ratio increased significantly in back row pile. The displacement distribution of piles group under vertical loads decreased with the increase of pile depth. It is little effect of batter pile inclination for each row of pile bearing capacity.(5) Based on similarity theory, in the model test the batter piles were loaded in the axial, radial, and inclined direction,considering different inclination angles of pile and pile shaft buried depth, and were measured displacement of pile top, soil stress distribution around pile, and pile shaft internal force change value, the 3×3 batter piles group with high-rise pile cap was loaded in horizontal or vertical direction, considering different inclination angles of pile. In each row piles, the internal force distribution of inclined pile and load share ratio are obtained, through comparison and analysis, the reliability of the theoretical analysis and numerical simulation method are validated. A more in-depth analysis on the working mechanism and property of batter piles foundation under various static loads was developed in model experiment.(6) In order to reveal seismic behavior of batter piles group with high-rise pile cap, taking three kinds of earthquake waves as example, the effect laws of inclination angle and free pile length on seismic response were analyzed based on three-dimensional elastic-plastic dynamic finite element model. The results show that the maximum axial force of pile appears in 2.5 m approximately beneath the maximum erosion line and the maximum bending moment is located in the interface between pile cap and pile shaft; The vertical displacement and Y-orientation bending moment are symmetrically distributed along the pile shaft, and acceleration, lateral displacement, axial force, and bending moment distributions along pile shaft are in the same trend. The greater free pile length, axial force of pile is larger and bending moment of pile is smaller. The greater inclination, axial force and bending moment of pile are larger. The influence on internal force is greater by the pile free length than the pile inclination. Subjected to the seismic load, acceleration and displacement of batter pile decrease, but its axial force and bending moment increase. The total bending moment of batter pile is controlled by Y-orientation bending moment. Therefore, in order to make the bridge superstructure displacement, acceleration as small as possible, the inclined pile structure seismic design should adopt the reasonable reinforcement design of inclined pile, with particular emphasis on the Y direction of bending moment.