A critical reappraisal of “preconsolidation pressure” interpretations using the oedometer test

Abstract

Over the past 70 years, a number of methods have been proposed for the interpretation of the characteristic vertical effective yield stress, or “preconsolidation pressure,” of compressible soils as defined using the standard oedometer test. The concept of the “preconsolidation pressure” has been extraordinarily useful in geotechnical engineering for analysing and predicting settlement behaviour and for normalizing other engineering parameters for comparative purposes. Defining this characteristic stress, however, is often problematic and relies heavily on graphical techniques that are subject to some uncertainty, particularly when using semi-log plots for this purpose. This paper illustrates fundamental difficulties with the interpretation of oedometer test and presents an alternative technique for defining unambiguous values of the vertical effective yield stress.

Discussion of “Accuracy of determining pre-consolidation pressure from laboratory tests”

“…) for the 11 graphical methods of interpreting pre-consolidation pressure, one of which was referred to as " Boone (2010)". Boone's method, however, has been oversimplified by the authors so that the method described in the paper does not match the instructions given by Boone (2010).…”

“…Boone's method, however, has been oversimplified by the authors so that the method described in the paper does not match the instructions given by Boone (2010). More specifically, according to Boone (2010), p is the intersection point obtained from the following two lines: (i) a line coincident with C cmax (maximum value of the slope of the virgin compression segment of the void ratio (e)-log( v ) curve) and (ii) a line parallel to C r (average slope of the unload-reload cycle of the recompression segment of the e-log( v ) curve) passing through the point ( v0 , e v0 ) where v0 and e v0 are the in situ vertical effective stress and void ratio at in situ vertical effective stress, respectively.…”

“…Boone's method, however, has been oversimplified by the authors so that the method described in the paper does not match the instructions given by Boone (2010). More specifically, according to Boone (2010), p is the intersection point obtained from the following two lines: (i) a line coincident with C cmax (maximum value of the slope of the virgin compression segment of the void ratio (e)-log( v ) curve) and (ii) a line parallel to C r (average slope of the unload-reload cycle of the recompression segment of the e-log( v ) curve) passing through the point ( v0 , e v0 ) where v0 and e v0 are the in situ vertical effective stress and void ratio at in situ vertical effective stress, respectively. The method described and used by the authors (as the intersection of tangent lines to the recompression and virgin compression segments of the e-log( v ) curve) seems to be appearing for the first time in the literature in Zeevaert (1973) and thus it will be referred to as " Zeevaert's (1973) (2005), intercomparisons of average model-performance error should be based on the mean absolute error (MAE).…”

Time-dependent behaviour of the Bearpaw Shale in oedometric loading and unloading

“…There are a number of different methods that have been developed to determine the pre-consolidation pressure, each of which has its own set of advantages and disadvantages. Recent work by Boone (2010) discusses the reliability of pre-consolidation pressures calculated through the different methods. During this work the pre-consolidation pressures were determined using the Butterfield (1979) method; however, manual calculations using the Casagrande (1936) method were used to verify the results.…”

Reply to the discussion by Kootahi on “Accuracy of determining pre-consolidation pressure from laboratory tests”

“…Nevertheless, the overall performance rankings based on the RD index are very similar to those from RMSE values. The only difference is that the rankings of the Boone (2010) and Onitsuka et al (1995) methods are switched (from the third to the fourth and vice versa). The large difference in rankings from RI values is because of the more favourable rating of RI for methods that are either very accurate or very precise.…”