Effective visual measurement system for SPT hammer energy measurement

Abstract

The Standard Penetration Test (SPT) is prone to variability due to complex energy transfer dynamics and equipment inconsistencies. Traditional force and acceleration measurements provide valuable data but fail to fully capture the multidimensional movement of SPT components. Therefore, visual measurements of SPT components using a Line-scan and High-Speed Camera (HSC) with target markers have been attempted, but these are limited to 2-dimensional movements. To address these limitations, this study presents a novel HSC system integrated with circular target markings, offering the measurement of movement of SPT component assembly in all three dimensions and Energy Transfer Ratio (ETR). Controlled laboratory SPT tests were conducted to validate the approach. Experiments were carried out for various range of N-values (N = 5 to R), where vertical displacement corresponds to varying soil relative densities (∼15–90 %) and penetration depths (∼60–3 mm) for a consistent ∼60 % input ETR. ETR was estimated using the proposed method and compared with traditional force and acceleration measurements obtained from the SPT Hammer Energy Measurement Apparatus (SPT-HEMA) at both the anvil and sampler levels. The vertical displacement from HSC matched within ± 0.1 mm of manual vernier-caliper measurements. The Comparison reveals strong agreement on displacement, velocity, and ETR values for all penetration resistance. The standard error in ETR values between HSC and SPT-HEMA was below 0.5 %. For the same rod length, lower N-values exhibit longer displacement and ETR durations, while higher N-values show shorter displacement duration and concentrated energy dissipation. The proposed approach improves accuracy in SPT dynamics and testing methodologies.