Dynamic performance of the Becker hammer drill and penetration test

Abstract

The Becker penetration test (BPT) blow counts are commonly correlated to the standard penetration test (SPT) N-values for foundation design and liquefaction potential assessment in coarse-grained soils. Most of the existing correlations, however, do not adequately account for the variable energy output of the ICE 180 diesel hammer used in the Becker system, and the shaft resistance acting on the Becker pipe is often ignored. To obtain reliable BPT–SPT correlations, an extensive study of the BPT has been conducted at several sites in British Columbia. Dynamic measurements of Becker drill rigs and penetration tests were conducted that included hammer combustion and bounce chamber pressures, as well as force and acceleration near the top of the drill pipe. The dynamic field data are presented, including the maximum energy transferred to the top of the Becker pipe (ENTHRU). An energy approach for correcting Becker blow counts to a reference ENTHRU level of 30% of the hammer-rated energy is proposed. Different combustion conditions, drill rigs, and pipe sizes are investigated in the study. The test results show that ENTHRU is a fundamental and useful parameter for normalizing the BPT blow counts to account for the variable energy transfer from the diesel hammer. Key words : penetration test, dynamic measurement, energy, pile driving, diesel hammer, stress-wave propagation.