Performance prediction relationships for AM2 airfield matting developed from full-scale accelerated testing and laboratory experimentation

Abstract

The AM2 airfield matting system is used by the U.S. military for temporary, rapidly constructed airfields. Predicting the number of allowable aircraft passes across an AM2 installation is challenging because of the complex design of the joining system and the fatigue behavior of the joints. Prior to this work, the prevailing methods used to predict the performance of AM2 were based on the CBR design procedure for flexible pavements using a small number of full-scale test sections over CBRs ranging from 4 to 10 percent and simulated aircraft that are no longer in service. This report presents results from nine full-scale experiments conducted on sections of AM2 matting installed on unstabilized soil and gravel subgrades with CBRs of 6, 10, 15, 25, and 100 percent, and provides improved relationships for predicting subgrade deformation underneath an AM2 mat installation and the associated fatigue damage when subjected to F-15E and C-17 traffic. Additionally, a laboratory fixture and procedure is described for evaluating an AM2 style joint in fatigue and relating its performance to given field conditions without requiring the expense of full-scale testing. These relationships are suitable for design and evaluation frameworks currently used for airfield pavements and matting systems. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.

Proposing an Updated AM2 Mat Performance Criteria Model

“…The full-scale test data used for calibrating the performance model are from the RPRE program, which conducted tests using F-15 and C-17 load carts on AM2 mats over Buckshot clay test sections of various subgrade CBR (12)(13)(14)(15)(16). A CBR value of 6 is the lowest subgrade stiffness used during the full-scale testing, so the authors used permanent deformation equations produced by Rushing (17)(18)(19) for the F-15 and C-17 aircrafts. The predominant failure mechanism at low CBR values is permanent deformation.…”

“…The reason for choosing these particular equations is that the primary failure mode of airfield mats over low subgrade CBR under aircraft tire pressures is permanent deformation, not mat breakage. The equations are from Rushing and Howard (17)(18)(19).…”

“…Furthermore, the performance curve was fitted using a simple logarithmic function with only two regression degrees of freedom. The primary reasons for not attempting to better fit the performance curve to the calculated points using the permanent deformation equations suggested by Rushing and Howard ( 17 – 19 ) is because (1) these points were not actual test data, and (2) sound engineering judgment says where uncertainty exists, be conservative in design. Lastly, the test data used in curve fitting included both single tire F-15 and multiple tire C-17 tire configurations over a wide range of subgrade CBR values.…”