Hypoplastic material constants for a well-graded granular material for base and subbase layers of flexible pavements

This paper presents the results of the first phase of a research project dealing with the constitutive description of the behaviour of well-graded granular materials when used for base or subbase layers in flexible pavement structures (so-called "unbound granular materials", UGMs). Monotonic and cyclic loading is under consideration. The present paper concentrates on test results and the constitutive description of monotonic loading. Hypoplasticity in the version proposed by von Wolffersdorff is used as the constitutive model. Sets of material constants for typical UGM materials do not exist in the literature. The experimental determination of a set of constants according to the procedure proposed by Herle is described in this paper. In the monotonic triaxial tests specimens with a square cross-section were used. The paper presents a preliminary test series comparing triaxial results obtained with cylindrical and with prismatic specimens. Re-calculations of the element tests are also presented. The simulations show a good congruence with the experiments.