Pore Pressure Dissipation Induced by High-Velocity Impacts of a Portable Free-Fall Penetrometer in Clays

Abstract

In situ pore pressure dissipation in soil primarily depends on the coefficient of consolidation and permeability of the soil. This study represents an initial effort to investigate pore pressure dissipation induced by high-velocity impacts of a portable free-fall penetrometer (pFFP), and to explore the applicability of existing solutions, developed for cone penetration testing (CPT), for estimating the coefficient of consolidation. For this purpose, pFFP data from four test sites across North America were reviewed, and the same pFFP was deployed in a large fabricated and instrumented clay sample. In the laboratory, pore pressure recordings from four pressure transducers placed in the clay sample surrounding the path of the pFFP were obtained in addition to recordings of the pFFP transducer in the u2 position. Pore pressure dissipation behavior in line with dilatory dissipation was observed, characterized by an initial increase in pore pressures and a subsequent decrease. The dissipation curves were interpreted using a square-root time extrapolation technique from the literature. The results suggest that the square-root time extrapolation technique appears suitable for the interpretation of data from pFFP dissipation tests. Challenges regarding obtaining high-quality pressure data using pFFP, as well as regarding full-scale testing in the laboratory, are discussed. Among other observations, the preliminary data suggest that data impacted by issues in the filter may be interpreted using the same technique, although it will lead to overprediction of the time to 50% consolidation.