Analysis of acceleration and excess pore pressure data of laboratory impact penetrometer tests in remolded overconsolidated cohesive soils

Free fall CPTu measurements have two data acquisition approaches: direct measurement of sleeve friction (f(s)) and tip resistance (q(c)) or estimation of these via acceleration data. However, enhanced impact velocities cause strain rate effects on the sediment, which requires to correct q(c), and f(s) for these rate effects. The pore pressure (u(2)), 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 f(s) and q(c). Additionally, we studied dynamic u(2)-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 u(2)-responses as increases in the modulus excess pore pressure. This will help to analyze existing and future u(2)-measurements.