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Previous studies by the authors have found that a cathead and rope when used to perform standard penetration tests (SPT) have resulted in energies reaching the striker plate or anvil substantially less than those resulting from a complete or 100% free fall. In fact, depending on variables such as the number of turns of rope around the cathead, the rope age, cathead speed, and method of rope release, none of which have been standardized in the SPT, variations in the delivered energy have ranged from 25 to 70% of the theoretical free fall. In order to eliminate such variability in the delivered energy, a new hammer and lifting device have been investigated for potential use as an alternative to the cathead and rope for the performance of the SPT.
The new lifting device used is composed of a hydraulic motor-operated spool with a wire line which not only raises the 63.5-kg (140-lb) hammer 762 mm (30 in.), but reverses the spool direction to permit efficient “free fall.” The new hammer used is a sleeve-type, enclosed 63.5-kg (140-lb) hammer that falls on an internal anvil. The lifting device and the hammer combination may be used in both the manual and automatic modes. The variables tested for these devices include the fall height, mode of operation, and inclination of the drill stem.
It was found that the delivered energy is proportional to the fall height, independent of mode and independent of the drill stem inclination up to 3 deg from the vertical, and gives about the same delivered energy as the cathead and rope with one or two turns on the cathead.
Recommendations for possible future standardization of this equipment for use with the SPT are given.
Associate professor of civil engineeringMember of ASTM, Purdue University, West Lafayette, Ind.
Geotechnical engineer, McClelland Engineers, Houston, Tex.
Project geotechnical engineer, Woodward-Clyde Consultants, Plymouth Meeting, Pa.
Stock #: GTJ10374J