Rutting failures are prominent in expedient airfields constructed with AM2 landing mats over soft existing subgrades. There are many issues that must be addressed when approaching this multiaceted problem. The load transfer mechanism occurring at interlocking mat joints and the mat-soil interface bonding condition affect near surface subgrade response. The repeated loading coupled with lateral aircraft wander causes significant principal stress rotation in the subgrade. This kneading action then causes variations in the excess pore-water pressure and a subsequent softening of the soil. The purpose of this study is to investigate the critical factors that lead to subgrade rutting failures in landing mats constructed over soft subgrades. A three dimensional finite element (3D FE) model of a landing mat system over soft subgrade is implemented under both static and pseudo-dynamic loading conditions with aircraft wander. To capture the complex stress histories induced by the simulated moving gear loads over the unique structural features of the AM2 mat system, an elastoplastic kinematic hardening constitutive model, the Multi-Mechanical Model, is developed, calibrated and used to represent the subgrade response. Under both static and pseudo-dynamic loading, the FE model results match very well with the stress and deformation results from full-scale instrumented testing of the AM2 mat over 6 CBR subgrade. 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. Furthermore, rotation of the principal stress axes and changes in excess pore-water pressures occur in the subgrade because of the moving tire load. These phenomena contribute to extension of the field of deformation influence around the trafficked area in the subgrade and upheaval at the edges of the test section. Findings of this study show that although layered elastic analysis 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. Furthermore, the proposed 3D modeling approach implementing aircraft wander can provide a reliable platform for accurately simulating the subgrade response under pseudo-dynamic loading conditions.

The U.S. military requires the ability to rapidly deploy troops, equipment, and materials anywhere in the world. Recent operations have brought attention to the need to utilize austere, unsurfaced, and sometimes sub-standard airfields within a theater of interest. These airfields may require additional taxiways and aprons. One option for the rapid construction of such is airfield matting systems. The focus of the work for this thesis was commercially available airfield matting systems to support large military transport aircraft, such as the C 17. Several test sections with differing strength soils were built with chosen mats tested in an elimination method, using a load cart that simulates contingency loading of one main gear of the C 17. Matting systems were evaluated based on logistical and assembly requirements, and deformation and damage sustained during traffic. A modeling effort was performed to investigate the potential of a simple model to predict the response of these matting systems under full-scale testing.