SPT Hammer Energy Ratio versus Drop Height

Abstract

Automatic trip hammers have advantages for standard penetration test (SPT) of consistent drop height and low friction loss during hammer fall. These advantages, however, generate high energy transfer ratios (ER), typically about 90%. This efficiency causes lower sensitivity and higher energy correction coefficients, CE . To reduce ER and CE and to increase the sensitivity of SPT conducted at the Wildlife Liquefaction Array (WLA) and the Garner Valley Downhole Array, instrumented Network for Earthquake Engineering Simulation sites, a 127 mm (5.00 in.) long sleeve was placed in the hammer mechanism to reduce the drop height from 762 mm (30 in.) to 635 mm (25in.) . To calibrate the energy for these drop heights, measurements were made for a series of SPT tests in Borehole X2 at WLA on November 21, 2003. For these SPT, sleeves were inserted with lengths of 50 mm (2 in.) , 127 mm (5 in.) 177 mm (7 in.) , and no sleeve. Resulting drop heights were 762 mm (30 in.) , 711 mm (28 in.) , 635 mm (25 in.) , and 584 mm...