chapter  76
Analysis of acceleration and excess pore pressure data of laboratory impact penetrometer tests in remolded overconsolidated cohesive soils
ByR. Roskoden, A. Kopf, T. Mörz, S. Kreiter
Pages 6

Free fall CPTu measurements have two data acquisition approaches: direct measurement of sleeve friction (fs ) and tip resistance (qc ) or estimation of these via acceleration data. However, enhanced impact velocities cause strain rate effects on the sediment, which requires to correct qc , and fs for these rate effects. The pore pressure (u2 ), an important parameter for evaluating soil properties, is not corrected for the penetration rate effects yet. Hence, a laboratory free fall calibration test, with a miniature cone penetration lance, which measures u2 and acceleration, was designed. The objective was to investigate responses of the acceleration—data to calculate kinematic fs and qc . Additionally, we studied dynamic u2 -responses for their penetration rate effect. We also investigated existing penetration rate-corrections for remolded, overconsolidated cohesive soils. In total six experiments were conducted, each of which consisted of four penetrations with impact velocities of 0.02 to 2 m/s. We estimated fs and qc from acceleration-data for a remolded, overconsolidated cohesive soil. New rate correction values have been found for this soil, which show a dependency on consolidation histories. Moreover, we identified possible rate effects on u2 -responses as increases in the modulus excess pore pressure. This will help to analyze existing and future u2 -measurements.