Becker and standard penetration tests (BPT–SPT) correlations with consideration of casing friction

Abstract

The Becker penetration test (BPT), through correlations with the standard penetration test (SPT), is widely used for foundation design and liquefaction assessment in gravelly soils. Most of the existing correlations, however, do not adequately account for the variable energy output of the diesel hammer used in the Becker system, and shaft friction on the Becker casing is ignored. An alternative and more rational approach to BPT–SPT correlations is presented, based on experimental and numerical studies conducted at the University of British Columbia. The research involves performing SPT, BPT, and other in situ tests at several sites in British Columbia and includes dynamic measurements of energy transfer in the SPT and BPT. Stress-wave measurements and wave-equation analyses are used to evaluate the effect of friction on the BPT blow count. New BPT–SPT correlations are proposed that consider the energy transfer in both tests and explicitly consider casing friction in the BPT. A recommended procedure for estimating equivalent SPT N60 from BPT blow count is presented. Key words : Becker penetration test, standard penetration test, dynamic measurement, pile driving, stress-wave propagation.

Liquefaction Resistance of Soils: Summary Report from the 1996 NCEER and 1998 NCEER/NSF Workshops on Evaluation of Liquefaction Resistance of Soils

“…Direct measurement of transmitted hammer energy could provide a more theoretically rigorous correction for Becker hammer efficiency. Sy and Campanella (1994) and Sy et al (1995) instrumented a small length of Becker casing with strain gauges and accelerometers to measure transferred energy. They analyzed the recorded data with a pile-driving analyzer to determine strain, force, acceleration, and velocity.…”

Investigation of Liquefaction Potential of Alluvium underneath an Earth Embankment Dam

“…Figure 6 presents, as an example, the equivalent SPT blow counts obtained from a pair of SPT and BPT borings located within about 3 m distance. The BPT blow count data were also reduced using the Sy and Campanella (1994) approach, which is based on direct energy measurements. In this study, the SPT-equivalent blow counts obtained using the two approaches were in good agreement.…”

Geotechnical and Foundation Aspects

“…Due to the high driving energy that is possible with this device, the test is appealing for use in very deep deposits. However, friction along the casing becomes difficult to evaluate properly in deposits deeper than about 30 m. In this case, the correlation of Harder and Seed [1986] in Figure 7.41, which incorporates friction intrinsically, may not be appropriate [Sy and Campanella, 1994]. Also, this correlation should not be used for sites with thick, dense deposits overlying loose sands or gravels because it has not been verified for these conditions [NCEER, 1997].…”