Re-examination of dynamic load tests on piles

The dynamic load test (DLT) and the rapid load test (RLT) on piles both pursue the full activation of pile capacity during the impact event and evaluate the pile capacity by measuring and analyzing the impact excitation and response signals of pile top. However, the both tests require 3~5 times different weights of drop mass or inertial reaction mass as well as distinct mechanical principles. Based on the hammer-pile-soil interaction model established under the combination of the traditional pile-soil interaction mode and the drop mass system, the analysis of wave mechanics, the proof of momentum theorem and the comparison of test cases show that the momentum and energy transfer of the hammer are related to the compressive resistance of the pile and influenced by the impedance ratio or mass ratio of the hammer and the pile and the side/tip resistance distribution of the pile. The influences of different side/tip resistances and impedance ratios on the energy transfer and impulse change and the dynamic phenomena relating to the level of the pile capacity, "pile-to-hammer bump", "pile run-away"and "higher efficiency of tip resistance mobilization for piles resting on hard bedrock than that of the static load tests under the equivalent energy consumption circumstances" are analyzed, which enriches the dynamic load tests on the piles. The principle defects of RLT are analyzed, and the integration of DLT and RLT is suggested.