Influence of procedural variables on the gradient ratio test

Ideally, filtration behavior of soil-geotextile systems as determined by th e gradient ratio (CIR) test (ASTM D 5101) should depend only on the soil an d geotextile properties. In practice, however, test results can vary substa ntially with slight variations in test details and procedures. In addition, some optional procedures can have a significant effect on test results, wh ile 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 sign ificant effect on filtration behavior. Chlorine algicide was effective in e nhancing long-term filtration behavior, as was purging with CO2 and slow sa turation of the system. Placement of the soil specimen also influenced GR v alues; they were found to be lower for compacted specimens than for loosely placed specimens. Presoaking geotextiles had no observable effect on filtr ation behavior, and disturbance of the GR device during the early stages of the test caused immediate and significant changes in permeability and GR.