Abstract
Piezocone testing was developed during the late 1970’s. It was based on the cone penetration test, (CPT), and piezometer probes of the time. This development occurred in various countries simultaneously. In this thesis the author describes his development of a piezocone system in South Africa during this period, as well as further developments up to the present system which is a sophisticated, computer based, realtime logging and interpretation system. During this development, emphasis has been placed on data quality and security as well as maximising the information from a piezocone sounding. One of the aspects of maximising the data was to record the start of a dissipation test at every stoppage, such as a rod change, and to terminate the dissipation test when probing was resumed. This resulted in numerous incomplete dissipation tests which, up to now, could not be interpreted and were therefore discarded. This led to a loss of potentially valuable information. The author has developed a dissipation slope theory which predicts that it should be possible to determine the coefficient of consolidation from the very first portion of the dissipation test. This theory was developed into an interpretation method for incomplete dissipation tests. The implementation of the dissipation slope theory necessitated a normalised theoretical dissipation curve. A number of researchers have presented such curves and their work is summarised in this thesis. The author developed a family of theoretical curves for a range of stiffness ratios based on the work of Randolph and Wroth (1979) and compared the result with a Biot-coupled consolidation (CRISP, finite element) analysis of the dissipation of the excess pore pressure distribution as predicted by the strain path method (Baligh and Levadoux, 1980). The dissipation slope theory was applied to field dissipation tests to compare the predicted coefficients of consolidation with backfigured and laboratory coefficients. A comparison between the conventional t50 method for the interpretation of long “complete” dissipation tests and the dissipation slope method was also made. It has been concluded that the dissipation slope method is a reliable method which can be used for the interpretation of all piezocone dissipation tests and that it should be the method of choice for dissipations in fast draining material. A further requirement for the implementation of the dissipation slope theory was that the ambient, or hydrostatic, pore pressure be known. A method was developed to determine the ambient pore pressure from incomplete dissipation tests through a process of curve fitting and minimising of error parameters. This has proven to be a valuable technique in its own right.