Preparation, Characterization and Modeling of Unbound Granular Materials for Road Foundations

A wide range of granular soils were laboratory prepared as base and sub-base materials in flexible pavements technology. The samples were produced according to the requirements defined in the Spanish General Technical Specifications for Roads and Bridge Works (PG-3), which links to the American Unified Soil Classification System (USCS). The lab-prepared granular soils were characterized by means of particle size distribution, Atterberg limits, non-standard Proctor and California Bearing Ratio (CBR). The determination of CBR has been performed considering the evolution of the penetrability up to one, two, three and four days of immersion. The results show that repeatable values within an acceptable degree of accuracy can be obtained, which indicates good quality laboratory testing conditions. Detailed analytical study is performed on the relationship between CBR index and maximum dry density, finding that a predicting model can be obtained from density variation to estimate representative CBR values for design. The results were compiled in a decision matrix using the Analytical Hierarchy Process (AHP) to estimate a California bearing ratio value (CBR) versus maximum dry density