United States Department of Transportation
i
324 Building Special-Case Waste Assessment in Support of the 324 Building Closure (TPA Milestone M-89-05)
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1998-05-12
[PDF-1016.65 KB]
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Abstract:An accelerated testing procedure was developed to evaluate performance of separation layers used between open-graded bases and lime stabilized subgrades. Significantly of concern was assessing separation layer performance in regard to the degree of pumping into the open-graded base and the magnitude of deformations occurring during testing. A pneumatically driven, electronically controlled, repeated loading laboratory apparatus was designed and constructed to perform the testing of these materials. A low plasticity clay and a silty clay till soil were tested in this research. The separation layers investigated included nonwoven geotextiles and a dense-graded base aggregate blend. Specimens were housed in a stiff wall plexiglas cylinder during testing. Tests were conducted at various loading levels and durations in order to develop the accelerated testing procedure. Comparisons of specimen deflection and pumping relative to non-separated test cases were made to determine the relative performance of the separation layers and the effect of different loading conditions. Ultimately, loading at levels upwards of 5 times expected in the field, for short durations (20,000 cycles or less) was performed to evaluate separation layer performance. Separation layer performance under these conditions can be compared to typical loading level performance provided relative measurements are used and it is understood the failure mechanisms may be different. Geotextiles consistently provided separation between the soils and open-graded aggregates though pumping of fines occurred. The dense-graded separation layer showed a marked drop-off in performance upon wetting of the material. Though the dense-graded layer often prevented the soil layer from intruding into the open-graded layer, the dense-graded layer itself intermixed into the open layer. A distinct breakpoint in performance occurred at a soil strength of CBR4 under accelerated testing. Soils below CBR4 showed considerable pumping and deformation while soils above that strength yielded minimal pumping and deformation regardless of separation layer type. Based upon performance comparisons with non-separated test cases, the use of a separation layer between lime stabilized subgrades and open-graded aggregate bases is imperative.
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