Simplified Dynamic Method for Pile‐Driving Control

Abstract

Despite recent advances made in the wave‐equation‐based approach for pile‐driving control, at the time of writing, the dynamic formulas, such as the Engineering News Record (ENR) formula and its various modified versions are still widely used. One of the major reasons for the poor performance of the dynamic formula method, besides its obvious simplifications in treating complicated wave propagation phenomenon during pile driving, is the uncertainties about the energy transferred to the pile during each hammer blow. Assuming that energy input from the pile hammer can be determined, an improved dynamic method is developed for estimation of shaft resistances and their distributions of an impact‐driven pile. The method is cast within the principle of energy balance, with consideration of both elastic energy and plastic irreversible work. An incremental and forwardmarching solution algorithm is developed to partially compensate for the negligence of loading/unloading behavior when complex tension and compression wave forms travel through the pile. A wave‐equation‐based numerical program is used in performing a series of parametric studies to identify the effect of shaft‐resistance distributions and to generate engineering correlations between blow count and pilepenetration conditions (maximum pile velocity and acceleration due to each hammer impact). A simple microcomputer‐based, user‐friendly computer program is developed for field application. Verification of the developed method for both prototype pile driving and dynamic small‐rod penetration is provided by a favorable comparison between the results of the proposed method and those calculated from the so‐called CAPWAPC procedure, based on the measured high‐strain test data.