Volume 22, Issue 1 (March 1999)
Influence of Procedural Variables on the Gradient Ratio Test
Ideally, filtration behavior of soil-geotextile systems as determined by the gradient ratio (GR) test (ASTM D 5101) should depend only on the soil and geotextile properties. In practice, however, test results can vary substantially with slight variations in test details and procedures. In addition, some optional procedures can have a significant effect on test results, while other required procedures appear to have little influence. A systematic study was performed to evaluate the effects of these procedures on GR test results. It was found that microfiltration of the in-flow water had a significant effect on filtration behavior. Chlorine algicide was effective in enhancing long-term filtration behavior, as was purging with CO2 and slow saturation of the system. Placement of the soil specimen also influenced GR values; they were found to be lower for compacted specimens than for loosely placed specimens. Presoaking geotextiles had no observable effect on filtration behavior, and disturbance of the GR device during the early stages of the test caused immediate and significant changes in permeability and GR.