Abstract:

The dynamic penetration index correction, test stability and relationship of blow-counts are closely related to the effective hammer impacting energy. Strain gauges and acceleration sensors were installed at the top of the probe rod and the probe, and the hammer energy of heavy and super-heavy dynamic penetration under different probe rod lengths was measured. The results show that when the single probe rod in the probe rod is short and there are many joints, the hammer energy of the probe rod calculated by the force square method (F2 method) with an integral domain of (0, 2l/c) differs greatly from the actual hammering energy, where l is probe rod length, c is wave velocity. Due to too many interference factors in the in-situ test, it is more reasonable to the force velocity method (FV method) that selects the first extreme value and the F2 method selects the time when the hammering axial force first passes through the zero point as the integral end time of hammering energy to calculate the hammering energy. As the length of the probe rod increases, the hammer energy reaching the probe decreases linearly. Blow-count converting coefficients for heavy and super-heavy hammer numbers under the rod lengths of 3, 5, 8 m, and 11 m are 2.285, 2.160, 2.440, and 2.810, respectively, which are basically consistent with the total potential energy ratio of super-heavy and heavy hammer.

Key words: dynamic penetration test, energy measurement, force-velocity method, force square method, axial impacting force