Behavior of Granular Materials Under Triaxial Compression with Pulsating Deviator Stress, HR-131, Special Report

Behavior of granular material subjected to repeated load triaxial compression tests is characterized by a model based on rate process theory. Starting with the Arrhenius equation from chemical kinetics, the relationship of temperature, shear stress, normal stress and volume change to deformation rate is developed. The proposed model equation includes these factors as a product of exponential terms. An empirical relationship between deformation and the cube root of the number of stress applications at constant temperature and normal stress is combined with the rate equation to yield an integrated relationship of temperature, deviator stress, confining pressure and number of deviator stress applications to axial strain. The experimental program consists of 64 repeated load triaxial compression tests, 52 on untreated crushed stone and 12 on the same crushed stone material treated with 4% asphalt cement. Results were analyzed with multiple linear regression techniques and show substantial agreement with the model equations. Experimental results fit the rate equation somewhat better than the integrated equation when all variable quantities are considered. The coefficient of shear temperature gives the activation enthalpy, which is about 4.7 kilocalories/mole for untreated material and 39.4 kilocalories/mole for asphalt-treated material. This indicates the activation enthalpy is about that of the pore fluid. The proportionality coefficient of deviator stress may be used to measure flow unit volume. The volumes thus determined for untreated and asphalt-treated material are not substantially different. This may be coincidental since comparison with flow unit volumes reported by others indicates flow unit volume is related to gradation of untreated material. The flow unit volume of asphalt-treated material may relate to asphalt cement content. The proposed model equations provide a more rational basis for further studies of factors affecting deformation of granular materials under stress similar to that in pavement subjected to transient traffic loads.

Consolidation of Loess, 1971

Effective stress paths for a loessial soil subject to collapse during confined compression have been determined from the results of a testing program consisting of (1) confined compression tests on natural samples of loess with initial water contents ranging from air-dry to saturation, (2) negative pore-water pressure measurements to -300 psi during these tests, and (3) Ko-tests in which the lateral stress ratio was measured for one-dimensional strain. Before collapse, Ko was found to average 0.23, an extremely low value for a loose soil, whereas after collapse, Ko increased to 0.54, which is consistent with values for other soils. Because of the low Ko-values before collapse, the effective stress path for loading in confined compression initially approaches the failure envelope. At collapse the stress path intersects the failure envelope and thereafter it changes direction as a consequence of the higher Ko-value after collapse. From the stress path interpretation of the results, it is demonstrated that the collapse mechanism of loess in confined compression and during wetting is a shear phenomenon and subject of analysis in terms of effective stresses.