Research On Response Of Pile Foundation Under Cyclic Lateral Loads

In practical engineering, pile foundations are not only subjected to its superstructure’s vertical load, but also subjected to significant cyclic lateral loads due to wind, waves or earthquakes. Many pile foundations have failed catastrophically owing to these cyclic loads, with the rapid development of social economy and the advances in science and technology, the technique standard and the rule of designing of the pile foundation design do not meet demand of the practical load requirements. For example, the horizontal bearing capacity of the pile that subjected to cyclic lateral loads are not provided dearlyin current codes. Therefore, studying the response of the pile foundation under cyclic lateral roads is necessary.Based on analysis of existing design data, parameters of the pile physical condition, soil properties and cyclic loading conditions of pile foundation are firstly selected herein. By using the large geotechnical finite element analysis software PLAXIS, different soil parameters, different load conditions and different physical conditions of pile foundation are considered respectively to study the behavior of the pile foundation under cyclic lateral loads. The stress-strain relationship of soil around the pile is fully used for analyzing the results, by adding a vertical force, coupling load response is also discussed on this paper. The main conclusions are as follows:(1).Soil deformation modulus of soil has a significant impact on single pile’s horizontal bearing under cyclic lateral loads. With the increase of the soil deformation modulus, the maximum bending moment of pile decreases and so as to the maximum horizontal displacements, which indicating that the increasing of the deformation modulus of soil help to improve bearing performance. In addition, the impact of the physical and mechanical properties of the surface soil pile is much larger than the subsoil.(2).With the increase of pile-soil stiffness ratio, the pile maximum bending moment and the maximum horizontal displacement tend to be larger. That is, dynamic response of horizontal displacement and internal force of the single pile increase with the increase of pile-soil stiffness ratio. The pile slenderness ratio is one of the main parameters that affect single pile horizontal dynamic response. When pile slenderness ratio is less than 20, with the increase of the pile slenderness ratio, horizontal dynamic response of the single pile decreases. When the ratio is 20,the response comes to the smallest. However, when the pile slenderness ratio is more than 20, single pile horizontal dynamic response along with the change of slenderness ratio is not very obvious. The single pile horizontal dynamic response is not decreases monotonously with the increase of pile slenderness ratio, that means there is a best slenderness ratio. In this paper, the best slenderness ratio is choosed as 20.(3).Load condition is the key factors that affect the internal force and displacement of pile foundation. In a certain range, the response of the single pile under cyclic horizontal load increases with the increase of cycling times, decreases with the increase of loading frequency and increases with the increase of load amplitude.(4).Under coupled loads, the small vertical force can offset part of the horizontal stress, limiting horizontal displacement of single pile. However, When the vertical force increases, the pile horizontal displacement and bending moment becomes larger. The existence of the vertical force which increases the vertical displacement, resulting in additional bending moment. This effect can not be ignored in the design of pile foundation.(5).Pile spacing has a direct impact on the reacting force of soil to the pile and pile load sharing in pile group foundation. This paper takes three rows of piles as example, the bigger the pile spacing, the smaller displacement and internal force of the front piles and the bigger the displacement and internal force of the middle and back piles. When it increases to a certain extent, the pile bending moment and shear force diagram curve shape become more and more similar, and closer to the curve of single pile. When the pile spacing is greater than 6 times of the pile diameter, the horizontal load of pile group effect is relatively weak and almost can be neglected.