Critical Factors in Subgrade Rutting Failures of Airfield Mats over Soft Soils under Static Loading

Subgrade rutting failures in matting structures present a unique challenge in expedient airfields. Mats are often constructed over existing soft subgrades and can experience aircraft with large gross loads and high tire pressures. It is important to understand and predict the critical factors that contribute to deformation in these thin structures. This paper presents the results of a comprehensive study on the critical factors contributing to rutting in the AM2 matting system under static loading, using a combination of full-scale instrumented testing, layered elastic analysis (LEA), and three-dimensional finite-element (FE) modeling. The FE model of the AM2 mat system is built by implementing a user-defined constitutive model, multimechanical model (MMM), to simulate the soft soil subgrade response. The MMM is a recently developed elastoplastic kinematic hardening model capable of capturing the soil behavior under complex stress histories. The results of the FE model are compared against those attained from a set of linear and nonlinear LEA and full-scale testing. The FE results show a good agreement with the LEA results and the measured data from earth pressure cells and single depth deflectometers. The FE model is then used in a series of sensitivity studies to explicate effects that factors such as loading conditions, subgrade cover material, mat joint load transfer, and mat–soil interface conditions have on deformation response. Results show that incorporating the load transfer mechanism occurring at the mat joints and varying the mat–soil interface condition affect the near surface subgrade deformation and stress responses that contribute to rutting failures. Findings of this study show that although the LEA procedures are the basis of current airfield design methodologies, critical design features and the corresponding deformation responses can be better modeled using the FE approach.