The issues relating to the measurement of deformation moduli of granular base materials by cyclic triaxial testing were examined. A special method of conducting cyclic triaxial tests, referred to as stress path cyclic triaxial (SPCT) testing, was introduced. SPCT tests were cyclic triaxial tests where the radial stress was cycled simultaneously with the axial stress along a constant stress increment ratio path. SPCT tests, compared to conventional cyclic triaxial tests, can better simulate the stress changes experienced by typical elements of granular base materials in a pavement system during a wheel pass. The performance of the special triaxial testing system was verified. The test results of three granular base materials were examined. The stress increment ratio, r, defined as the ratio of change in radial stress to change in axial stress, has a significant influence on the strain responses during cyclic loading. A parameter referred to as the Proximity Index was found to be most relevant in influencing the behaviour during cyclic loading. Provided that the value of the Proximity Index is less than 0.7, the strain responses can be modelled by a cross-anisotropic elastic model. However, the anisotropic elastic parameters were correlated to both the number of loading cycles and the mean stress level, and did not take a unique value. (a).
Abstract