An oedometer test study on the preconsolidation stress of glaciomarine clays

Abstract

Stress history is usually determined by interpreting the results of oedometer tests to obtain the preconsolidation stress using traditional methods such as those proposed by Casagrande and Janbu. Both these methods are based on the assumption that the soil experiences a change in stiffness, from a stiff response to a soft response, close to the preconsolidation stress. Disturbed soils, however, especially overconsolidated clays of low plasticity, exhibit a soft response at low stresses, thereby making the interpretation of oedometer tests using traditional methods extremely difficult. Using data mainly from the Haltenbanken area, offshore Norway, a study was undertaken to investigate the various methods and testing procedures available to determining stress history. Oedometer verification tests were also performed on reconstituted specimens to compare interpreted values with the actual applied preconsolidation stress. This paper describes the results of the study by illustrating the variation in the interpretation methods and testing procedures used to determine preconsolidation stress.Key words: preconsolidation stress, yield stress, overconsolidated, low plastic clays, oedometer test, stress history.

Overpressure within upper continental slope sediments from CPTU data, Gulf of Lion, NW Mediterranean Sea

“…Results r 0 p from laboratory tests Preconsolidation pressures r 0 p obtained following Casagrande's (1936) and Onitsuka's (in Grozic et al 2003) methods (Fig. 4a, b) are shown in Table 3, where they are labelled r 0 pa and r 0 pb , respectively.…”

“…Laboratory oedometer consolidation tests are usually conducted on small samples assumed to be undisturbed. However, almost all recovered samples have some degree of disturbance (Grozic et al 2003;Lunne et al 2006) and, consequently, the laboratory-derived strength and consolidation parameters may not be entirely representative of the in situ soil conditions. In situ tests are performed under existing stresses and boundary conditions in the field, providing more accurate and reliable results than laboratory tests.…”

Effect of Temperature on Shear Strength and Yielding Behavior of Soft Bangkok Clay

“…Grozic et al (2003) analyzed the diŠerent methods for determining preconsolidation pressure and show that the strain energy methods proposed by Crook and Graham (1976) provided the most consistent overall results. Therefore, the strain energy method was used in this study to determine accurately the temperature eŠect on preconsolidation pressure.…”

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

“…The results are presented in Table R1. As these calculations (as well as those presented in the paper) include consolidation test data from several other studies (Becker et al 1987;Grozic et al 2003Grozic et al , 2005Jose et al 1989;Sridharan et al 1991), the values of MAE, E, and RI as well as the corresponding rankings differ from those reported by the discusser. This is also indicated by the smaller number of analyses in Table D1 of the discussion (Kootahi 2017) compared to those in Table R1.…”

“…Such bi-logarithmic graphs are easily produced with most graphing software packages (e.g., MS Excel). Grozic et al (2003) also compared the ease of use and simplicity of the Casagrande (1936), Onitsuka et al (1995), and Becker et al (1987) techniques. Although Grozic et al did not investigate the specific bilogarithmic method of Oikawa (1987), they found a similar bi-logarithmic technique (Onitsuka et al 1995) to be the most accurate and the least difficult approach for estimating p while Casagrande's method proved to be one of the most difficult and least accurate methods by largely overestimating p,i .…”