Case Study: Correlation between Becker and SPT Blow Counts

This paper presents the results of a site-specific study correlating Becker penetration test blow counts to that of the standard penetration test. The study was conducted as part of the Woodfibre LNG export facility project. The project site is located near Squamish, British Columbia. Site investigation for the project included standard penetration tests, Becker penetration tests, and instrumented Becker penetration tests. The blow count values from the three different test methods needed to be converted to equivalent standard penetration test values for use in seismic analyses and design of the various LNG infrastructure types. Four different methods and correlations were evaluated. Comparison of the equivalent blow-count data obtained from adjacent boreholes with different test methods shows wide differences in the resultant equivalent standard penetration test values obtained using currently available conversions methods. We propose site-specific conversion factor to correlate blow-count data from the different test methods for sand and gravel soil types. This paper also presents a framework to correlate the bounce chamber pressure and hammer energy measurements, which can be used to convert the blow counts from Becker penetration tests to equivalent standard penetration test values.