TESTING METHODS FOR DETERMINING THE DEFORMATION BEHAVIOR OF ROAD GRANULAR MIXTURES ACCORDING TO THE REQUIREMENTS OF EUROPEAN STANDARDS

Abstract

Introduction. In the introduction to the paper, the effect of deformation behavior of unbound granular mixtures (UGMs), when used in an unbound base layer, on the construction of the flexible road pavement was outlined. Problem statement. The issues of the paper concern the problems related to the unstable deformation behavior of UGMs in unbound base/subbase layers during flexible road pavement designing and maintenance. Purpose. The main goal of the paper is to perform an analytical review of methods for testing and modeling of deformation behavior of UGMs. The results of the analytical review are intended to be used during implementation of a national standard concerning the method of testing of unbound granular mixtures by the triaxial cyclic loading identical to the related European standard. Results. The analytical reviewing led to the following results: it was revealed that at each stress level the most stable conditions are ensured to each UGM in its post-compaction period when the rate of accumulated permanent strains becomes negligible and the plot of permanent strain versus the number of loading cycles takes an asymptotic form; it was concluded that the main task of the UGM testing by triaxial cyclic loading shall be resolved as the evaluation of the loads (stresses) that, accepting all the input data, ensure the stable condition of the mixture in an unbound layer of the designed flexible road pavement; the test consists of applying the cyclic stresses corresponding to their expected limits to the cylindrical specimen of UGM and of measuring the axial and radial strains of the specimen induced by these stresses; it was stated that the effective prediction of deformation behavior of UGMs and also their classification to relate the category of deformation behavior of UGM to the expected stress level can be performed through various mathematical models based on “permanent deformation/stress” dependency.