Oedometer Test Data Research Articles

Fragipan formation in loess soils: development of the Bryant hydroconsolidation hypothesis

The formation of fragipans is still a matter for investigation and discussion. Bryant (Soil Sci. Soc. Am. Spec. Publ. 24, 1989, pp. 141–150) suggested that the `hydroconsolidation' process (structure collapse when loaded and wetted) may contribute to fragipan formation. Experimental studies of the collapse behaviour of both undisturbed and model loess soils are reported. These demonstrate that the `small clay' model of hydroconsolidation advanced by Rogers et al. [Eng. Geol., 37 (1994) 83–113] appears to explain many aspects of the collapse of loess soils when loaded and wetted. This `small clay' model can reconcile the Bryant suggestion with collapse observations, and in so doing can satisfy all of the important criteria governing the formation of fragipans. In particular it can explain the constant depth of occurrence. The `small clay' model requires the soil structure to collapse under the control of a critical and limited clay mineral content. Too much or too little clay does not allow collapse to occur, as indicated by oedometer test data for both undisturbed and reconstituted loess soils under simulated field conditions. The fragipan should form in a metastable soil, one capable of some linear collapse.

Interpretation of Oedometer Test Data for Natural Clays

ABSTRACT Two alternative approaches to the conventional e—log p method for determining yield stress are critically examined in this paper, and their advantages and limitations are identified. The yield stresses defined in both alternative approaches are also theoretically verified as identical for the oedometer test data. A comparison of the advantages and limitations of both alternative approaches suggests that the In (1 + e)-log p approach should be used to interpret the oedometer test data for natural clays, and the defined yield stress can be interpreted as being responsible for the critical state of structure collapse. Systematic analyses on the oedometer test data for undisturbed Ariake clays and Shimabara clay demonstrate that it is valid to use the In (1 + e) – log p approach for determining the yield stress and both the compression and swelling indices of natural clays. In addition, some analysis implications are also given for useful parameters, such as, the critical-state pore pressure parameter in predicting the undrained strength of overconsolidated clays and the compression index ratio in evaluating the aging effect of natural clays. Finally, Nagaraj’s sample disturbance degree concept based on oedometer test data is extended to take into account both the effects of stress release and mechanical disturbance. The analysis results indicate that the defined degree of sample disturbance can reflect the combined extent of stress release and mechanical disturbance during sampling and handling.

Work as a criterion for determining in situ and yield stresses in clays

A method of interpreting conventional oedometer test data using work per unit volume as a criterion for determining both in situ effective and yield stresses in clay is presented. This technique was applied to the results of oedometer tests carried out on samples of natural clay deposits and on specimens consolidated anisotropically from a slurry to a known effective stress state. The work per unit volume – effective stress relationship, using arithmetic scales, can be approximated or fitted using linear relationships. The intersections of these fitted lines are demonstrated to provide accurate values for in situ current and yield (preconsolidation) stresses. The yield stress is defined as the intersection of the initial fitted line and the linear relationship observed at higher stresses. The current effective stress is indicated by the first significant divergence of the data from the initial fitted line. These relationships apply to both conventionally (horizontally) trimmed specimens and to vertically trimmed oedometer samples. It is hypothesized that the in situ effective and yield stresses (in both the vertical and horizontal directions) in a natural clay can be determined by the work per unit volume interpretation of oedometer tests carried out on horizontally and vertically trimmed specimens. Key words: in situ, stress, yield, oedometer, interpretation, clays, work, state, K0, preconsolidation pressure.

A Computational Method for Consolidation-Coefficient

ABSTRACT The theoretical consolidation curve based on Terzaghi’s theory has been successfully represented by a simple explicit algebraic equation. The use of this equation has been extended by obtaining an expression for consolidation-coefficient involving selected three oedometer test data. This method, unlike the existing one, does not require the use of graphs or charts and it can be effectively used on a digital computer.

Extended use of oedometer test data. Technical note : 4F, 3R. J. Geotech. Engng. Div, V100, GT9, Sept. 1974, P1075–1080

Extended use of oedometer test data. Technical note : 4F, 3R. J. Geotech. Engng. Div, V100, GT9, Sept. 1974, P1075–1080

Extended Use of Oedometer Test Data

This note presents a method for estimating the primary consolidation settlement of clays with an axially symmetrical load using modified oedometer test data. The solution is theoretical; its limitations when applied to real soils are examined subsequently.