Stress Path and Permanent Deformations in Sand Subjected to Repeated Load

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Courtesy of ASTM International

The development of permanent deformations in soil has been studied by a number of researchers using triaxial systems. In most cases soil specimens were subjected to a pulsating axial stress while the confining pressure was maintained constant. This loading path simulates a very limited number of practical cases. Thus, there is a question as to the generality of the results obtained from conventional laboratory studies.

Presented is a study of the effect of stress path on the development of permanent deformations in sand. Using a pneumatic servo-controlled triaxial system, the confining pressure was varied simultaneously with the axial load. Six different straight line stress paths were investigated; three under compression and three under extension conditions. Dry Ottawa sand was subjected to 100 000 sinusoidal loading cycles at a frequency of 1 Hz. Several loading intensities were used in each stress path.

A linear relationship was observed between the permanent axial strain and the logarithm of the number of loading cycles, for constant repeated stress magnitude and constant stress path. Furthermore, based on the results presented here, one can utilize the conventional constant confining pressure triaxial tests to estimate the effect of stress path. Consequently, the results of the conventional tests can be generalized.

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