Measurements of driving energy in SPT and various dynamic cone penetration tests

Abstract

Driving energy was measured in a standard penetration test (SPT) and 12 types of dynamic cone penetration tests (DCPTs) having different configurations for the hammer, driving rod, anvil and cone tip. The driving energy transferred from the free falling hammer to the driving rod was estimated from the measurements of strain and acceleration below the anvil. Basically, the driving energy was estimated for 21 successive blows in order to obtain the mean value, the standard deviation (σ) and the coefficient of variance (COV) in the SPT and DCPTs. The dynamic cone resistance, qdyn, was estimated from the driving energy, the corresponding set per blow, and masses of the hammer and the total rods. Thus, the estimated dynamic cone resistance was compared with the static cone resistance, qt, from a cone penetration test (CPT). The main objective of this report is to provide information on the driving efficiency in the SPT and each DCPT. The mean values for ef in the tests ranged from 52% to 76%. The values of COV for ef ranged from 0.024 to 0.265. Even though the test results are limited, the dynamic cone resistance, qt, estimated from the dynamic measurements were relatively good measures of the cone resistance from the CPT, showing the importance of the dynamic measurement in the SPT and DCPTs.In addition, possible factors influencing the driving efficiency, such as the hammer mass, the configuration of the driving rod (solid or hollow), the ratio of the diameter of the anvil and the diameter of the hammer, and the existence of a cushion or cushions between the anvil and the hammer, are discussed on the basis of the limited test results.