ONE-DIMENSIONAL LOADING-RATE EFFECTS

It has long been recognized that the one-dimensional or uniaxial strain response of most soils subjected to high-intensity transient loads (i.e., blast pulses) differs from the response measured under quasi-static loading rates. Recent research has suggested that for submillisecond rise times, increases up to 10-fold in the loading constrained modulus occur for some remolded partially saturated granular soils under undrained conditions. Parallel research has shown that, in contrast, loading-rate effects can be ignored for a similar granular material tested under nearly identical boundary conditions. Stress-strain curves from 60 uniaxial strain tests are summarized and presented herein depicting the behavior of three soils (two clean sands and a silty clay) to a variety of loading rates. Loadings are typically carried to 10,000 psi (69 MPa) with times to peak ranging from a few tenths of a millisecond to several minutes. These laboratory test results show that a dramatic increase in the loading constrained modulus does not occur for the rise times examined. Rather, a gradual stiffening occurs as the time to peak pressure decreases. The maximum ratio of the dynamic-to-static loading constrained modulus is observed to be about a factor of two for the soils tested. Based upon these test results, a strain-rate and strain-level dependent modulus stiffening model is developed. This model is implemented into a one-dimensional plane wave propagation computer code to predict the results of field tests that are performed using two of the three soils tested in this study. A comparison between the laboratory-based model predicted behavior and response obtained from the field tests is favorable. © ASCE.