Q

How are the energy quantities for the PDA (EMX, EFV, ETR and ETH) and for the SPT Analyzer (EMX, EFV, ETR, E2E, E2F, EF0, EF2, EV2) calculated?

A

EMX is calculated as the maximum of the integral of force times velocity, over the whole record. It is the best theoretical method for calculating the maximum energy transferred to the foundation or SPT rod, and is the only one approved by American Society for Testing and Materials (ASTM) 4633 and European Standard ISO 22476-3 for SPT energy calculations. Because it searches the whole record, it is independent of the length (LE) setting. The EMX value is compared with the rated energy of the hammer to calculate ETR, that is, ETR (%) = 100 * EMX/PE, where PE is the maximum rated potential energy of the hammer. The PDA also calculates ETH, which can be used only with open end diesel hammers. It is defined as ETH(%) = 100 * EMX/(Wr * STK), where Wr is the weight of the ram, and STK is the open end Diesel stroke calculated by the PDA based on the time between blows. EFV is exactly the same as EMX, and is provided for consistency with ASTM D4633 terminology. The E2E method does the same computation as EMX, but it stops the integration at (2 * LE)/c. It can be used to stop the integration at a time corresponding to a given LE setting. It should be noted that ending the integration before the end of the record is not the procedure recommended by ASTM 4633 and European Standard ISO 22476-3 for SPT energy testing, and that changing LE will also change the capacity calculations on PDA testing. EF2 was used exclusively for SPT energy measurements on previous versions of ASTM D4633, at a time when a reliable method for measuring the velocity on SPT rods was not available. It is the maximum of the integral of the square of the force divided by the impedance, over the whole record, and is based on the theoretical proportionality between force and velocity along most of the first 2L/c period on SPT energy tests. In real practice this proportionality is hard to achieve due to non-uniformities along the rod, imperfect joints, etc. Other factors also affect the accuracy of this method, so several correction multipliers had to be used. It was later recognized that these correction methods did not yield reliable results (please refer to the Appendix on ASTM D4633 for further information). EF2 is therefore generally inaccurate and obsolete, and should not be used . EF0 is the same as EF2. The E2F method does the same computation as EF2, but stops the integration at 2L/c. It has the same lack of accuracy as EF2. EV2 is the maximum of the integral of the square of the velocity multiplied by the impedance, over the whole record. It is based on the same proportionality principle as EF2, so it suffers from the same lack of accuracy. We would like to stress that EF2, EF0, E2F and EV2 should not be used to determine the energy transferred to an SPT rod or to a foundation, and are provided for research purposes only.