Improved Methods for Rapid Load Tests of Deep Foundations

Rapid Load Tests have been promoted as an alternative for Static Pile Load Tests since the late 1980s. Rapid Load Tests create a relatively long duration force pulse in comparison with Dynamic Load Tests. However, a reliable prediction of pile static capacity with this test based on the so-called Unloading Point Method (UPM) has been subject to debate. Estimates of static capacity by UPM have overestimated static load test results when the applied force pulse produced too little axial movement. To resolve these issues, a drop mass Rapid Load Test called the Hybridnamic Test (HT) was developed with a ram mass up to 700 kN to reliably estimate the pile static ultimate bearing capacity up to a 35 MN. This paper discusses using a multi-cycle Hybridnamic Test in soil of mostly sand. A new interpretation method called Fully Mobilized UPM, with a required minimum net penetration per test cycle, was applied to this case study and comparison of estimated soil resistance was made between conventional UPM and Fully Mobilized UPM, and with signal matching of the dynamic force pulse data using CAPWAP. Finally a practical method to prepare a Static Load-Displacement Curve based on multi-cycle HT results is proposed.