Experimental analysis of critical void ratio concept in artificially cemented sands

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Virginia Polytechnic Institute and State University


This report presents the results of analyzing the critical void ratio concept on weakly cemented sand. The study consists of drained triaxial compression tests performed on artificially cemented sands created to simulate the natural behavior. In order to carry out this study, loose samples were prepared and subjected to different confining pressures such that failure at volumetric contraction could be obtained.

The triaxial test results showed that the samples exhibited similar response to drained loading as compared to previous investigations on the static behavior of naturally and artificially cemented sands.

Following the empirical method of determining the critical void ratio by plotting volumetric strain at failure against void ratio after consolidation, interpolation of the data points yielded critical void ratios of 0.735, 0.722, 0.703 and 0.668 for confining pressures of 60, 70, 80 and 95, respectively. A comparative analysis was made by plotting instantaneous void ratio during the loading against axial strain and this yielded values of 0.745, 0.735, 0.715 and 0.685 for confining pressures of 60, 70, 80 and 95 respectively. However, this method depends on the test accuracies at strain levels beyond 20% where the specimen becomes severely distorted, thus, making this method unreliable to use.

Utilizing the result from volumetric strain-void ratio curves, the relationship between volumetric strain at failure and confining pressure was plotted and yielded critical confining pressures of 125, 94, 78, 67 and 60 psi for void ratios after consolidation of 0.66, 0.68, 0.70, 0.72 and 0.74, respectively.

From the above results, the critical state line, which shows the variation of the critical void ratio, ecrit with the magnitude of the cr1 critical confining pressure, σ₃crit, was defined for the artificially prepared samples with one percent cement. It would be interesting to compare this result with the critical state line of uncemented samples and of samples with higher amounts of cementation.

The critical state concept is very important in evaluating the undrained strength of sands from drained tests data. The reader is referred to reference 7 since this is beyond the scope of this investigation. This concept is also an important study used in determining the liquefaction potential of sands. A paper by Castro [2] reported that liquefaction can only occur in sands that are looser than the critical state. The results of consolidated-undrained static tests will indicate whether the sand is looser or denser than the critical void ratio for the appropriate confining pressure, and thus whether the sand is susceptible to liquefaction.

The reliability of the parameters obtained depends on a very limited number of data points. The author suggests that more tests on a wic!er range of relative density and confining pressure should be conducted to obtain more data points where a more accurate interpolation or extrapolation could be done. However, the results presented in this report are hoped to provide useful information for further studies to be made on the analysis of critical void ratio concept in cemented sands.