Modeling of piles in a ground environment

Abstract

Most modern engineering programs use the finite element method to implement static analysis. This method can be used to model piles. The features of modeling a pile foundation are considered using the example of the Robot Structural Analysis (RSA) software package from Autodesk.

The pile is created as a rod to model rigid coupling. When using the finite element method, the bar in the soil is divided into sections with a length of about 1 m, so that the necessary parameters can be assigned at different depths. For such a model, two approaches can be implemented. Let's call them conditionally: «method of elastic supports» and «method of elastic bar».

The method of «elastic supports» for RSA was proposed by Carlos E. Villarroel [1]. The idea is that at the nodes of the bar (along the pile depth), supports are created with elastic foundation coefficients in the horizontal (X, Y) and vertical (Z) planes. This coefficient (kN/m) in the direction of the X, Y, Z axes are obtained as the product of the base stiffness (kN/m3) by the corresponding area (m2). Areas are taken: along the lateral surface of the pile (for the Z-axis) and the vertical cross-section of the pile (for the X, Y axes). In addition, an elastic support is created directly at the tip of the pile, directed along the axis of the pile (Z). Here, the elastic foundation coefficient is obtained as the product of the foundation stiffness (at a given depth) by the pile cross-sectional area.

The «elastic bar» method consists in creating finite element bars on an elastic foundation for pile sections. Elastic foundation coefficients (kN/m2) are calculated as the product of foundation stiffness (kN/m3) by the reduced pile width (m). Thus, the work of the pile is ensured in the horizontal direction (X, Y). The work of the pile in the vertical direction is provided by creating a point support on the tip with the appointment of elastic compliance in the direction of the Z axis.

Using both methods, the example presented in [7] was calculated. The discrepancy in the results turned out to be quite acceptable for engineering calculations (for forces – 1,5-3 %, for displacements – 4,3 %).