Definition of new stopping criteria for the characterization of permanent deformation of granular materials

Abstract

In the characterization of the plastic deformation of granular materials for pavement use, it is possible to identify different behaviors throughout the load application in the triaxial equipment. In certain stress pairs, some soils may present very small accumulated deformation variations, reaching accommodation, not requiring the application of thousands of load cycles, as suggested in the Brazilian approach. In this sense, a preliminary assessment of this type of behavior can save time and resources in paving works. Therefore, the objective of this paper is to analyze the applicability of shakedown classification criteria for soils from a sampling region and to determine the effect of prior disruption in single-stage testing, in case of accommodation. For this purpose, 58 tests were analyzed for 7 soils, applying 9 stress pairs and 150,000 load cycles at a frequency of 2 Hz. The rutting calculation in a pavement section suggested that, for soils whose total deformation was less than 2 mm, stopping the procedure after about 30,000 cycles would generate approximately 0.1 mm variations compared to the values obtained at 150,000 cycles. Realizing that the criteria available in the literature would not be adequate for Brazilian standards and soils, Decision Tree models were used, based on ranges of vertical strain rate values at different intervals prior to 10,000 cycles. The results demonstrated that the algorithm was able to accurately predict the occurrence of Type A tests, with no false positives observed for the other plastic accommodation ranges. Thus, the application of the proposed methods in combination can provide significant economy and optimize the design and construction of Brazilian road pavements.