Analysis Of Driving Of Foundation Piles

Abstract

Abstract A computer method has been developed to analyze the driving of foundation piles by impact and vibration, with the hammer acting at any point along the pile. A mandrel or follower may be included in the analysis. While retaining the discrete-element concept proposed by E. A. L. Smith, the method employs an implicit (Crank-Nicolson) type of numerical solution. Soil supports may be any desired nonlinear functions of pile displacement history. Degradation in ultimate soil resistance under the action of inelastic rebound and reload of the pile may also be introduced. Introduction The analysis of pile driving requires some method of modelling, or simulation, of the hammer, the pile, and the supporting soil. The dynamic interaction in the system includes the elements of hammer impact, wave propagation along the length of the pile, and soil resistance associated with movement of the pile. Methods of dynamic pile driving analysis most commonly used in practice are based on work by E. A. L. Smith (Ref 1). Smith utilized the advent of the digital computer to perform a one-dimensional computer simulation of the behavior of the system consisting of the hammer, the pile, and the soil. This method has become widely known as the "wave equation" analysis. The name is somewhat misleading because this analysis is a discrete-element mechanical analogy of pile driving which does not directly employ the conventional mathematical equation for one-dimensional wave propagation within the solution process. The pile driving problem requires numerical flexibility to handle varied boundary conditions, soil restraint forces, and non-uniform cross-sections which cannot be accommodated with the use of closed form mathematics. A more appropriate method of analysis is a numerical discrete-element solution such as Smith proposed. However, there has been some concern expressed recently about the accuracy of driveability analysis (Ref 2). Discrete-element concept, the present method employs an implicit (Crank-Nicolson) type of numerical solution to yield the desired computational accuracy, stability and reliability. There has been an increasing demand in the industry recently for a rational pile driving analysis to include a more flexible driving system. In the present method of analysis, the hammer can act anywhere along the pile, and a mandrel or follower may be included in the analysis. In order to account for forces other than those from the direct impact of the hammer system, a force-time relationship can be prescribed by the user at any desired point along the pile. The soil supports are not limited to an approximate, simple elasto-plastic shape. They can be any nonlinear function of the pile displacement history, to reflect the actual soil response along the pile. The system is allowed to rebound and reload inelastically. A degradation in the ultimate soil resistance under the action of this rebound and reloading may also be included.