Determination of Bearing Capacity of Cleared and Graded Areas at Airports

Abstract

Aircraft veer-off is a lateral excursion from the runway. The cleared and graded area (CGA) outside a runway is provided with graded bearing capacity to stop veered-off aircraft. However, no precise design standards about the gradation of bearing capacity in the CGA are provided. This study attempts to address these deficiencies by proposing the division of CGAs into strips of specified widths and bearing capacities, decreasing toward the outside. The CGA division into strips is based on a risk assessment procedure based on historical worldwide veer-off accidents (1980–2016). Probabilities and consequences associated to side distances run by aircraft veered off from the runway centerline (CL) were assessed. Risks were computed by combining probabilities and consequences. Three CGA strips were proposed at different distances (30–50, 50–65, and 65–105 m) from the CL. The California bearing ratios (CBRs) associated to each CGA strip were determined through a veer-off simulation model, considering different exit angles, soil properties, and other characteristics. Among the different considered combinations of CBRs compliant with current regulations, those deemed to provide the safest aircraft stopping (at given exit angles and weight conditions) were set to 17, 16, and 15 for each strip. Additional safety measures were proposed as well.