Performance Prediction of Contingency Airfields Subjected to Repetitive C-17 Loadings

The U.S. Army Engineering Research and Development Center is investigating methods to construct a contingency airfield for C-17 aircraft loadings within a 72-hour construction period. The proposed method to satisfy these stringent design requirements is to use a chemically stabilized in-situ top soil layer as a runway surface. A suite of soil-chemical mixture combinations was examined to optimize the stabilized soil mixture behavior. A numerical approach is developed in this study to supplement limited C-17 full-scale testing data. Three stabilized soil mixture types are investigated using as stabilizing agents: 6% cement, 4% cement, and 4% cement + 1.5-in. (38-mm) long polypropylene fibers. Unconfined compression tests under monotonic loading and unconfined compression tests using repeated load tests were conducted to evaluate the stabilized soil mixture for strength and durability. Results have shown that the stabilized soil mixture exhibits damage and plastic behavior. In this study, the Army Corps' finite element code STUBBS is enhanced by including material damage to predict stabilized soil behavior when subjected to repetitive loadings. Damage behavior in the Valanis numerical model is calibrated using only two material properties and two damage parameters. Preliminary work on incorporating plastic behavior to supplement damage is discussed. In earlier work, forces induced by a C-17 aircraft on a runway were limited to a vertical force. However, C-17 aircraft braking forces induced during landing are substantial. Therefore, in this work, in addition to the vertical pressure exerted by the aircraft wheels, preliminary work is presented which considers an aircraft braking force.