An approach for nonlinear contact surface analysis and application to pile installation

摘要

This paper presents a novel Lagrangean approach for the analysis of nonlinear contact surface for rotationally motioned rigid body to a deformable body. The approach is physically sound based, since it relies on the simple application of the equations of motion. Their integration forces the contact grid points to move along a predefined shape function that represents the contact surface, unless separation occurs. The success of the approach is examined for the installation of pile with nonlinear tip end. Overall, it is believed that this approach could be utilized for many other installation problems, including problems where the motion of the penetrating body is not defined in time. In particular, it was found that the shape of the pile tip highly affects the resulted stress path in the soil domain when the upper end of the tip passes the depth of the adjacent points. There is some evidence that this effect influences even more than the friction properties along the shaft. Even more important observation is that the required penetration depth that allows complete mobilization the Nc value, is highly dependent on the ratio between the shear modulus G and the undrained shear strength CM. Stiffer clays require more depth to reach a steady state value of Nc. This evidence cannot be revealed by any of the steady state approaches for installation problems or by limit analysis which, inherently, do not take into account the rigidity of the soil. It is suggested that these methods will be applied for the pile installation method, only if the initial embedment of the upper end of the pile tip is deeper than the steady state front as designated in figure 5.