A Comparison of the Instrumented Becker Penetration Test (iBPT) to Existing Methods for Liquefaction Potential Assessment of Gravelly Soils at a Southern California Dam

The Becker Penetration Test (BPT) is an industry standard tool for characterizing and assessing the liquefaction potential of gravelly soils. However, the BPT has challenges estimating the resistance of soils beneath the driving shoe because a variable and unknown percentage of the energy delivered via the hammer is absorbed by shaft friction. A new instrumented BPT (iBPT) is capable of directly measuring the energy delivered to the soil beneath the driving shoe, thereby eliminating the uncertainty that shaft friction introduces into conventional BPT results.
An extensive field testing program carried out at a dam in Southern California included six clusters of BPT, SPT, CPT and Sonic boring data. Data collected at the dam site is analyzed in four ways using iBPT, SPT, CPT and BPT data (interpreted via Harder and Seed, 1986). The performance of the iBPT system is analyzed against the three industry standard methods in order to show that iBPT testing is necessary to reliably characterize gravelly soils underlying this and many other dams.