by Geoff Warren. This paper was first published in GE’s March 2007 issue.
Parameter determination from dynamic probe data has long been an uncertain and debatable subject within the geotechnical community. On a recent project a super heavy dynamic probe (DPSH) was used to obtain data in granular material, chalk and clay. The critical aspect is the conversion of DPSH data (blow count n) to standard density and strength data for design purposes, which in our case were standard penetration test (SPT) N values in granular material and chalk and undrained shear strengths of clays.
Initially it was thought this would be a straightforward matter of getting the equivalence from the drilling companies who supplied the equipment. But as the questions were asked it rapidly became clear that the whole subject of exact equivalence of the DPSH data to SPT N values and undrained shear strengths was a poorly understood area. Clear guidelines on equivalence did not exist and a review of available literature produced surprisingly few papers on the subject.