Energy measurements for Standard Penetration Tests and the effects of the length of rods

摘要

The need to measure the energy transmitted to the rod composition to correct and uniform the number of SPT blows is now fully recognized by the engineering community. The present paper extends the existing theoretical approach based on the energy content of the first compression wave and introduces an analysis for large displacements that aims at determining the influence of the length of rod in the measured N_(spt) values. The study is based on calibration chamber tests with energy measurements in three different positions: immediately below the anvil, at the mid-height of the composition and immediately above the sampler. Both experimental and analytical results demonstrate that the energy efficiency is inversely proportional to the length of rod. However, it also demonstrates that for long rod composition penetrating a soil with low resistance, the contribution of both rod weight and the permanent sampler penetration should be considered when computing the total energy delivered to the soil-sampler system.