Abstract:
Dynamic penetration test(DPT)is an in-situ testing technique used to evaluate the uniformity and density of soil layers. The drop hammer systems vary across different countries and regions, and the blow counts of DPT is significantly affected by factors such as soil layer friction resistance and energy loss, requiring corrections before further application. This paper conducts parallel experiments with heavy and super-heavy dynamic penetration tests at gravelly soils sites in the Chengdu Plain to explore the impact of different drop hammer systems and energy transfer on the number of blow counts. The ratio of effective transferred energy between heavy and super-heavy DPT is 0.39, and the ratio of the number of blow counts between super-heavy and heavy DPT is 0.4, showing a good proportional relationship. This provides experimental evidence for correcting the DPT number of blow counts using transferred energy. The drop hammer energy of heavy DPT is smaller, and due to the influence of larger diameter gravel or cobblestones, the DPT curve tends to show a rapid increase in the number of blow counts followed by a quick return to the normal trend; in the same gravelly soils site, the number of blow counts in super-heavy DPT changes consistently with depth, showing higher repeatability and reliability. Developing devices that can measure the transferred energy at the cone tip of DPT rod and exploring the effects of sidewall friction force and energy loss on the number of blow counts, the energy transfer coefficient at the cone tip of super-heavy DPT decreases from 62.5% at the ground surface to 55% at 10 m depth. The energy transfer coefficient at the cone tip is a comprehensive test indicator that reflects the impact of the drop hammer system, test process, friction resistance, and energy loss, providing a new approach based on cone tip energy measurement for correcting the number of blow counts.