The knowledge of the preconsolidation pressure, p′e, of an overconsolidated clay is of vital importance in the settlement analysis of structures. It has been found that the semigraphical methods to determine p′e proposed by Casagrande, Burmister, and Schmertmann are not completely satisfactory for sensitive clays. Also, the standard oedometer test is not adequate to fully describe the strain-effective stress behavior of such clays. Renewed interest in this topic by several investigators has shown that the magnitude of the preconsolidation pressure is greatly affected by the rate of loading, type of loading, specimen size, and type of testing apparatus used.
This paper reports on the results of a comparative study of consolidation behavior using two types of clays and four different testing techniques. The first series of tests was carried out on undisturbed specimens of soft Leda (Champlain Sea) clay cut from block samples and the second series was performed on prepared and consolidated kaolin specimens. For each series, four different consolidation apparatuses were used: a standard oedometer, a modified Rowe cell, an Anteus apparatus, and triaxial K0 tests. Both Leda clay and kaolin specimens were tested in parallel. Several sizes (diameters) of specimens and different loading techniques were used. Based on these test results, it was shown that the controlled gradient consolidation test using the Rowe cell with a softer membrane was the most suitable technique to establish a well-defined effective stress-strain curve. The controlled gradient test using the Anteus apparatus also gave a well-defined stress-strain relationship, but the operational procedures were found quite cumbersome. The K0-triaxial test was quite time-consuming and an elaborate recording of data was required. The results from standard oedometer tests, even using a modified loading, did not yield continuous effective stress-strain plots and p′e was difficult to determine. Also, a comparison of the coefficients of consolidation was made for the two clays and the various testing techniques employed.