Comparison of Pore Pressure Parameters from Piezocone and Dilatometer

Abstract

The Piezocone (CPTU) and the Marchetti Flat Plate Dilatometer (DMT) provide a number of empirical correlations for the purpose of soil identification. Each tool has defined a pore pressure parameter. For the piezocone, the parameter Bq ‘is based on the penetration pore pressures, the corrected tip resistance, the total overburden stress, and the existing hydrostatic pore pressure. This index has been used to characterize soil behavior rather than the actual soil type. For the dilatometer, the parameter Ud is based on the corrected pressures p0 and p2, calculated using the A and C readings and the existing hydrostatic pore pressure. This index can be combined with the material index ID to help with soil identification. Results from several test sites provide a promising direct correlation between Bq and UD, which can be used to enhance the identification of soil types by simply using the C-reading when performing DMT tests. Although the C-reading has been grossly ignored by users of the DMT, this new development will encourage measurement of this reading which provides similar trends to the pore pressures measured by the CPTU. The latest DMT equipment allows for the automatic measurement of the C-reading, which will assist in developing and enhancing existing correlations. This paper will present results at test sites located on opposite coasts of the USA. The trends of the Bq and UD indices are shown to be remarkably similar in all types of soils.

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