ANALYSIS OF HAMMER ENERGY TRANSFER RATIO OF STANDARD PENETRATION TEST

Hammer efficiency is defined as the energy transfer rate, and is an important index in standard penetration test to evaluate site bearing capacity and to assess liquefaction potential. In standard procedure outside China, the energy transfer rate is usually obtained by real in-situ testing using an energy measurement equipment, and then to correct blow counts. In Chinese codes, however, the energy transferred into the rod during hammering is not considered instead that the uncorrected blow counts are used in engineering practice, which leads to blow counts of standard penetration test obtained in China can hardly be compared with others. To solve this issue, three typical testing sites in Xichang earthquake experiment site are selected to test the hammer efficiency used in the Chinese routine standard penetration test equipment and to evaluate stability of energy transferring. The analytical results indicate that the energy transfer ratio is remarkably stable that the average energy transfer ratios exceed 75%. A slight trend of energy transfer ratio increasing with depth is delineated that the incremental of the energy transfer rate stays about 10% in the depth range of 20 m. The energy transfer ratio obtained in the tests can be used to evaluate the current standard penetration test apparatus.