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|Title:||Validation of soil-strength criteria for aircraft operations on unprepared landing strips|
|Authors:||U.S. Army Engineer Waterways Experiment Station.|
|Keywords:||U.S. Army Engineer Waterways Experiment Station (WES) - Technical Report -|
Corps of Engineers -
California Bearing Ratio
|Publisher:||Cold Regions Research and Engineering Laboratory (U.S.)|
U.S. Army Engineer Waterways Experiment Station.
|Series/Report no.:||Technical report (Waterways Experiment Station (U.S.)) ; no. 3-554.|
Summary: Tentative soil-strength criteria for the operation of aircraft on unsurfaced soils, as established by the U. S . Army Engineer Waterways Experiment Station and the U. S. Army Engineer Division, Ohio River, are based on California Bearing Ratio (CBR) values. In order to validate the tentative soil- strength requirements, the Waterways Experiment Station participated in aircraft operational tests conducted by the Air Force Operational Test Center at two test sites, Eglin AFB, Florida, and Pope AFB, North Carolina, which consisted of unprepared, sandy soil with sparse vegetation. The C-123B, a single -wheel, two-engine, troop-and-cargo transport, and the C-130A, a multiple-wheel, four-engine turboprop, heavy transport, were used in the tests. Gross loads ranging from 38,000 to 48,000 lb and from 80,000 to 116,000 lb, and main-gear tire-inflation pressures ranging from 41 to 90 psi and from 55 to 60 psi were used in the tests of the C-123B and C-130A, respectively. Penetrometer readings obtained at the two sites before and during the tests were correlated vdth CBR and converted to approximate CBR values. Conclusions were that : (a) both the C -123B and C -130A can operate successfully on sand subgrades with surface ruts as deep as 4 to 6 in.; (b) the average soil strength for the 6- through 12-in. depth can be used for evaluating the load-carrying capacity of a sand subgrade; (c) increasing wheel loads at constant tire-inflation pressures up to 116,000 lb had little or no effect on depth of ruts; (d) increasing tire pressure for a constant or increasing wheel load resulted in more severe rutting and disturbance of the sand subgrade; (e) minimum subgrade strength requirements (based on average strength values for the 6- through 12-in. depth), as determined from tests with C-123B and C-130A aircraft, were in good agreement with strength requirements indicated by the previously developed CBR design curves; and (f) tentative strength criteria established by WES and ORDL for the operation of aircraft on unsurfaced soils are as good as can be established from data available at the present time.
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