Study On Behavior Of Vertically Loaded Single Batter Piles

For the vertically loaded batter pile, the pile head not only produces settlement but also generates horizontal displacement, the cross section of pile shaft exists not only axial force but also larger bending moment and shear force, which make its behavior much more complicated than vertical pile. However, at present, there is no reasonable design theory for batter pile and its design theory still draw lessons from the theory of vertical pile, which obviously doesn’t reflect the practical working behavior. Consequently, a thorough understanding the practical working behavior of batter pile is essential for engineering design.In this study, firstly, a series of model tests were conducted to explore the effect of the pile shaft inclined angle and the pile length to its diameter ratio(L/D) on the settlement, pile head horizontal displacement, vertical ultimate bearing capacity of batter pile, pile shaft axial force, bending moment, shear force, skin friction as well as the ratio of tip resistance to the pile head load. And also, the behavior of batter piles was compared to that of vertical piles. The test results indicate that the settlement of batter pile subjected to vertical load is greater than that of vertical pile, the bigger the inclined angle as well as the larger the L/D ratio, the greater the settlement for batter pile over the vertical pile. A bigger inclined angle will result in a smaller ratio of bearing capacity and a bigger ratio of settlement. The axial force of batter pile subjected to vertical load is less than that of vertical pile, the bigger the magnitude of the inclined angle and the ratio of L/D, the greater the rate at which the axial force reduces along pile shaft for the batter pile. The maximum bending moment of batter pile increases with the increasing of inclined angle as well as the ratio of L/D, but the depth at which the maximum bending moment occurs is only associated with the ratio of L/D. The bigger the pile shaft inclined angle, the bigger the maximum skin friction on pile shaft; the larger the ratio of the L/D, the smaller the maximum skin friction on pile shaft. The maximum skin friction always occurs at a depth of one fourth to fifth pile length below the pile head.Then, the behavior of vertically loaded single batter piles was simulated using a finite element code, ABAQUS. The effect of pile shaft inclined angle, the pile length to its diameter ratio, the modulus ratio of pile to soil on the behavior of single batter piles was analyzed. The numerical results show that when the pile shaft inclined angle as well as the pile length to its diameter ratio are the same, the smaller the compression modulus of pile side soil, the bigger the settlement and pile head horizontal displacement, but the smaller bearing capacity; the larger the compression modulus of pile end soil, the smaller settlement of batter pile, but the greater bearing capacity. The modulus ratio of pile to pile side soil has a significant effect on the pile shaft bending moment, shear force, soil pressure and skin friction of the batter piles, while the effect of the modulus ratio of pile end soil to pile side soil is less significant.Finally, a calculation method of vertical ultimate bearing capacity and settlement for batter pile was developed based on the model tests and numerical analyses results, which is feasible in engineering application.