Hammer Energy Measurement of Standard Penetration Test in China

Hammer efficiency, which is defined as the energy transfer ratio, is an important index in standard penetration test which is widely used for measurement of soil penetration resistance and subsequent correlation with soil properties. In the routine procedure, the energy measurement should be made to correct penetration blow counts. However, the energy correction for standard penetration test are not considered in Chinese codes. To circumvent the shortcoming, in-situ tests at three selected sites in Xichang city region are performed to measure the energy transmitted into rod during hammer fall in the current commonly used standard penetration test setups. The energy transfer ratio data recorded are well consistent, that most energy transfer ratio values range in 60% to 90% with mean ratios exceeding 70%. The dependence of energy transfer ratio on testing depth is weak. The energy transfer ratio increases by about 10% when the penetration depth increases down to 20 m beneath surface. The analysis results can prove the reliability of current standard penetration test setups and provide a good reference for energy correction of blow counts.