SIMPLIFICATION OF SUBGRADE RESILIENT MODULUS TESTING

The standard test method (AASHTO T274) for the resilient modulus of cohesive soils can be simplified without affecting the reliability of flexible pavement design by the AASHTO Guide. The traffic life prediction accuracy (standard deviation) of the AASHTO design equation is equivalent to a resilient modulus testing accuracy of about 30 percent. The overall prediction accuracy is not affected substantially as long as the testing error (standard deviation) is 15 percent or less. Three cohesive soils were tested to examine the effects of confining pressure, deviator stress, number of stress cycles, and compaction method. For routine design the standard method of test can be simplified by (1) reducing the number of confining pressures from three to one (3 psi is suggested); (2) reducing the number of deviator stress levels from five to one (8 psi is suggested); and (3) reducing the number of stress cycles from 200 to 50. With these test simplification measures, the time required for testing (excluding sample preparation and test setup) is reduced from 100 minutes per specimen to less than 2 minutes.