Twentieth Canadian Geotechnical Colloquium: Recent developments in the Becker penetration test: 1986-1996

Abstract

The Becker penetration test (BPT) has proven to be a versatile and practical tool for characterizing coarse-grained soils. The most important factors affecting BPT interpretation are performance of the diesel hammer used in the Becker drill system and soil friction acting on the casing during the penetration test. Major developments in BPT from 1986 to 1996 are described in this paper. Extensive recent field measurements of hammer performance and casing friction are presented. The field data show that transferred energies in the BPTs are variable and depend on the drill rig hammer system, driving system, and combustion and ground conditions. The data also indicate that HAV180-type rigs give higher transferred energies than AP1000-type rigs. Casing friction measurements show that shaft resistances are variable and erratic, but that friction values in gravelly soils are generally less than those in sandy soils for the same embedment. A recently developed pull-up test using a tension load cell to directly measure casing friction shows considerable promise. Finally, a case study of a vibro-replacement project in coarse gravelly soils in which BPT was used for compaction specification and control is presented. The field measurements show, for the first time, that BPT casing friction in densified ground is significantly higher than that in undensified ground. This emphasizes the importance of considering casing friction in BPT interpretation for quality control of densification projects.