The corrections to account for the changes in the cross-sectional area and for the restraint of the membrane during a triaxial test may vary considerably depending on the actual behavior of the soil specimen. This paper shows how observations and measures can lead to a choice of corrections which are in good agreement with the true behavior of the soil-membrane system both for bulging failures and for failures along a shear plane. The data obtained by compression tests on rubber and rigid dummies offer a valuable basis for quantifying the required area and membrane corrections. An example illustrates the merits of the proposed corrections and shows that different interpretations of the membrane correction may have an important implication on the effective stress cohesion intercept.
The present paper reports on the failure of a test embankment built on a soft, sensitive, and cemented clay in Saint-Alban, Quebec. The embankment was built as a first stage of a research program aimed at studying the short and long term behavior of embankments on soft clay foundations.A complete description of the embankment, of the instrumentation, and of the failure is given, followed by the analysis of the failure performed on the basis of different assumptions of fill behavior and of vane strength values mobilized in the clay crust. The analyses show that the assumptions of full mobilization of friction in the fill seems to be the most representative of the fill behavior in the present case and that a suitable factor of safety is obtained only when a reduction of vane strength is assumed to act in the crust.A new approach based on the residual undrained strength is suggested and seems to offer some potential as a valuable means of analyzing the stability of embankments on clay foundations.
The detailed analysis of the pore pressures generated during construction under the center lines of four test embankments on a soft sensitive clay indicates a significant departure from the classical methods of pore pressure prediction.In the early stages of loading, the clay is overconsolidated and is characterized by a high Cv. As a result a significant consolidation occurs even in the very short duration of the construction. Due to this consolidation the vertical effective stresses increase rapidly until they reach the preconsolidation of the clay. At this point the clay becomes normally consolidated, and further loading occurs at constant effective vertical stress.The YLIGHT model of clay behaviour proposed by Tavenas and Leroueil may be used to fully understand this behaviour.In Part II, it will be shown that these findings apply in fact under most embankments and a prediction method will be proposed.
This paper presents the results of a study of stability by effective stress analysis of four embankments that were built to failure; three of these embankments are located in Narbonne, Lanester, and Cubzac in France, and the fourth one in Saint-Alban, Québec. After an outline of the procedures followed to obtain the required data and parameters, a brief discussion is presented on the defects inherent in the methods of analysis in terms of effective stresses. The factors of safety obtained by the effective stress analyses are compared with the results of total stress analyses. It is concluded that, in spite of the limitations of the method of effective stress analysis, this approach, as used in the present paper, remains a useful tool for the engineer.
The new approach to the stability analysis of embankments on sensitive clays, which is presented in this paper, is based on an interpretation of Bjerrum's data made by Mesri, which led to the observation that the available strength at failure under an embankment is nearly independent of the plasticity index and is a function of the preconsolidation pressure of the clay deposit. The new method is found to give good results in sensitive clays, but does not seem to be applicable to soft layered organic, cohesive soils.
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