Predicting California Bearing Ratio from Trafficability Cone Index Values

California bearing ratio (CBR) soil strength measurements are commonly used by the U.S. Air Force to identify locations suitable for use as expedient runways. Field CBR testing is a time-consuming operation requiring a skilled operator, and can be hazardous for the evaluation teams in hostile environments. Limited amounts of published CBR data are available. The measurement of trafficability cone index (CI), widely used by the U.S. Army for similar applications, is a process that is fast and simple, and for which a vast amount of published data worldwide are available. This report describes methods reported in the literature to correlate CBR to CI based on Unified Soil Classification System (USCS) soil type, as well as a systematic program to develop an algorithm to predict CBR from CI using a database of measurements of both CBR and CI made concurrently by the U.S. Army, many of which were taken in undisturbed soil. The database is described and related soil properties, such as plasticity information, soil density, specific gravity, and moisture content, are given. The original document contains color images.