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Alternative methods for providing a stable platform over soft subgrades were evaluated using a 1.4-km section along a Wisconsin State highway that incorporated 12 test sections to evaluate 9 different stabilization alternatives. A variety of industrial by-products and geosynthetics were evaluated for stabilization. The industrial by-products included foundry slag, foundry sand, bottom ash, and fly ash as subbase layer materials. The geosynthetics included geocells, a nonwoven geotextile, a woven geotextile, a drainage geocomposite, and a geogrid. The same pavement structure was used for all test sections except for the subbase layer, which varied depending on the properties of the alternative material being used. All test sections were designed to have approximately the same structural number as the conventional pavement structure used for the highway, which included a subbase of granular excavated rock. Observations made during and after construction indicated that all sections provided adequate support for the construction equipment and no distress was evident in any part of the highway. Each of the alternative stabilization methods, except a subbase prepared with foundry sand, appear to provide equivalent or greater stiffness than that provided by control sections constructed with excavated rock. However, the foundry sand subbase is providing adequate support. Analysis of leachate collected from the base of the test sections shows that the by-products discharge contaminants of concern at very low concentrations.

This paper describes a case history where the structural support afforded by a fly-ash stabilised layer was accounted for explicitly during the design of two flexible pavements. Pavements were designed and constructed at two sites in southern Wisconsin employing a layer stabilised in situ with fly ash. One pavement is for a residential subdivision. The other is a test section located in a secondary highway that was recently reconstructed. A control test section employing a conventional cut-and-fill approach was also constructed in the secondary highway. Fly ash was used to increase the strength and stiffness of the fine-grained subgrade at both sites, which was soft prior to stabilisation. Pavements at both sites were designed using the 1993 American Association of State Highway and Transportation Officials (AASHTO) method for flexible pavements so that their structural number would be equivalent to that of the conventional pavement originally called for in the design. Measurements of California Bearing Ratio (CBR) and resilient modulus (Mr) were used with the correlation charts for granular sub-base materials in the AASHTO manual to define layer coefficients for the stabilised layers. Tests were also conducted on specimens collected during construction to verify that the in situ mixture had similar properties to those anticipated during design. The pavement at these sites is being monitored seasonally using a falling weight deflectometer and pavement distress surveys. The monitoring programme has indicated that the pavements constructed with fly-ash stabilised layers provide comparable stiffness to conventional pavements employing a cut-and-fill approach. No signs of distress have been observed in the pavements constructed with a stabilised layer. Thus, assigning layer coefficients for fly-ash stabilised soils based on correlations for granular sub-base materials appears reasonable until layer coefficients specific to fly-ash stabilised soils become available.