Determining field bearing resistance of subgrade soils using physical characteristics

Abstract

Abstract In highway design, subgrade strength is mostly affected in pavement layers’ thickness. California Bearing Ratio (CBR) is one of the simple testing methods that is commonly used to determine the strength of unbounded paving materials; i.e., subgrade, subbase, and base course materials of highways and airfield pavement. In-situ CBR test is intended to determine the static properties of unbound pavement layers represented by bearing capacity of subgrade soils without requiring the digging of test pits. The in-situ CBR test is laborious, time-consuming, and relatively expensive, therefore an alternative methodology is proposed for correlating CBR value with physical properties of subgrade soils such as field density and moisture content. Three testing methods were used: in-situ CBR test, sand replacement method for determining the field density and moisture content of granular soils and clayey soils, respectively. Selected types of soils were nominated from the local area having soil’s type of A-l-b, A-3, and A-6-7. Statistical analyses were performed to evaluate bearing resistance of subgrade soils depending on water content and dry density obtained from field density tests. The results of two statistical models indicated that both field density and water content correlate well with the bearing ratio for various subgrade soils.