An Analysis of Different Methods for Assessing Selected Subgrade Material under Aircraft Pavements

Typically, in aircraft pavement design, the subgrade is assumed to be of infinite (semi-finite) thickness and is characterized by a single modulus (E), CBR value, or k value. In poor subgrade conditions a selected subgrade material may be utilized to overlay the subgrade to achieve an improved strength, or to achieve the required finished surface level. In this situation, an analysis of the various subgrade materials is typically undertaken to determine the effective subgrade strength at the top of the improved subgrade for use in the pavement design. The analysis usually considers the strength of the underlying material types, depth of the selected subgrade material, characteristic strength of the selected subgrade material, and the applied design loading. There are many different techniques available for assessing subgrade materials under aircraft pavements to determine the elastic characterization and effective subgrade strength. The methods identified for assessment in this paper include Austroads Guide to Pavement Technology Part 2: Pavement Structural Design (AGPT02-17); Queensland Department of Transport and Main Roads (DTMR); Japan Road Association; UK Defence Estates’ Design and Maintenance Guide 27: A Guide to Airfield Pavement Design and Evaluation (DMG27); and using Design Software analysis. This paper aims to analyze these methods under a theoretical consistent aircraft pavement profile to compare the results. The outcomes of the paper will help guide engineers’ understanding of the different methods available, and assist with making decisions for determining the most suitable method for assessing the effective subgrade strength of selected subgrade material over poor subgrades for pavement design.