|Title||Use of 'Zero Controlled Gradient' tests to determine EOP compression behavior|
|Publication Type||Journal Article|
|Year of Publication||2004|
|Authors||Sheahan TC, Degroot DJ, Fu Q., Ryan R.|
|Journal||Geotechnical Testing Journal|
|Keywords||compression index, consolidation, preconsolidation stress, soil consolidation tests, Soil sampling, soil structure, strain rate, Stress strain relations|
This paper describes the use of a new consolidation testing method, known as the “zero controlled gradient” (zero CG) test, to measure the one-dimensional (1-D), end-of-primary (EOP) consolidation behavior of soft soils. The conventional incremental loading (IL) consolidation test remains the most common test method for measuring 1-D consolidation behavior; however, data reduction requires graphical constructions to obtain key consolidation parameters. In addition, the IL test provides data only at intervals dictated by the loading increments used, leading to discontinuous stress-strain data that may mask or distort true soil consolidation behavior. The zero CG test mimics the EOP behavior by maintaining approximately zero excess pore pressure throughout the soil specimen as it is being continuously loaded, and thus avoids the problem of strain rate selection in the constant rate of strain (CRS) test. Zero CG tests were performed on three natural soils using a computer-automated Rowe consolidation cell, and these results were compared to conventional IL consolidation tests on the same soils. In general, for a given soil, the results from the two tests were consistent. However, the zero CG results had these advantages: defining the compression curve more accurately and continuously around the preconsolidation stress (σ′p), and giving higher, more realistic compression index values beyond σ′p. The major drawback of the zero CG test is that coefficient of consolidation (cv) data cannot be obtained due to the lack of excess pore pressure. The zero CG test offers both a practical and research tool for determining EOP consolidation states, and can eliminate strain rate problems inherent in both IL and CRS tests.