Deformation analyses of Florida highway subgrade sand subjected to repeated load triaxial tests: Pumphrey, N D; Lentz, R W Trans Res RecN1089, 1986, P49–56

Abstract

Laboratory repeated load triaxial tests are conducted to estimate the effects of highway traffic on the permanent and resilient deformation of a subgrade sand commonly used as a foundation for a flexible highway pavement structure in Florida. Combinations of confining stress and cyclic principal stress difference (test variables) and of dry unit weight and moisture content (sample variables) are used for each sample and loaded to 10,000 cycles. Confining stress, cyclic principal stress difference, and dry unit weight are correlated with permanent strain and resilient modulus and thus affect deformation properties of these soils. However, moisture content correlates with neither permanent strain nor resilient modulus. Static tests are conducted on various samples similar to those used in the cyclic tests. These results are used to normalize cyclic stress and strain at 10,000 cycles. A regression model is developed for predicting cyclic strain in the sand from satic tests by using a technique previously developed by Lenz. The model is compared to one for Michigan highway subgrade sand. Using a general linear test at a level of significance of 0.05, it is found that the data sets from each sand cannot be pooled to form one reression model. Values of resilient modulus after 10,000 loading cycles for the Florida sand ranged from 16,000 psi (110 240 kPa) at 5 psi (34.5 kPa) confining stress to 56,000 psi (385 840 kPa) at 50 psi (344.5 kPa) confining stress.