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.

A study was conducted to define an equivalency criterion for five materials used for working platforms during pavement construction on a poor subgrade: conventional crushed rock (referred to as breaker run) and four alternatives (Grade 2 gravel, foundry slag, bottom ash, and foundry sand). A layer of alternative material was considered equivalent if the total deflection of the alternative material was equal to that of breaker run under the same construction loading. Total deflection data for the equivalency assessment were obtained from a large-scale model experiment (LSME) simulating a prototype-scale pavement structure. Total deflections obtained from the LSME were checked against deflections measured in the field with a rolling wheel deflectometer and with an analytical method developed for unpaved roads. Design charts were developed for selecting the equivalent thickness of alternative working platform materials so that the alternative and a layer of breaker run provided equal deflection.

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A study was conducted in the field and with a large-scale model experiment (LSME) to evaluate the structural contribution of a 0.30-m-thick geosynthetic-reinforced granular layer used as a working platform for construction over soft subgrade. The study was conducted in the context of the 1993 AASHTO design guideline, in which the structural number (SN) of the pavement is based on layer coefficients (each defined using a resilient modulus). Working platforms reinforced with geosynthetics had smaller elastic deflections and larger elastic moduli than unreinforced working platforms with the same thickness. Reinforcement factors obtained in the field ranged from 1.2 to 1.8; those obtained in the laboratory ranged from 1.7 to 2.0, with greater reinforcement factors for the less extensible geosynthetics (geogrid, woven geotextile) for a 0.3-m-thick granular working platform. Of the four geosynthetics tested, the geogrid resulted in the greatest increase in modulus. Reinforcing the working platforms with geosynthetics resulted in increases in layer coefficients ranging from 50% to 70%. Similarly, increases in SN for a typical pavement structure were realized, ranging from 3% to 11% when all other factors were equal.

Large-scale experiments were conducted on working platforms of crushed rock (breaker run stone or Grade 2 gravel) overlying a simulated soft subgrade to mimic conditions during highway construction where a working platform is used to limit total deflections because of construction traffic. Tests were conducted with and without geosynthetic reinforcement to evaluate how deflection of the working platform is affected by the presence of reinforcement, type of reinforcement, and thickness of the working platform. Four different geosynthetics were used: geogrid, woven geotextile, nonwoven geotextile, and drainage composite. Reinforced working platforms deformed at a slower rate, and, in most cases, deformation of geosynthetic-reinforced working platforms nearly ceased after approximately 200 loading cycles. Total deflections at 1,000 cycles were smaller by a factor of approximately two for reinforced working platforms relative to unreinforced working platforms, and smaller deflections were associated when less extensible geosynthetics were used for reinforcement. The thickness of a geosynthetic-reinforced working platform needed to meet a target deflection diminished approximately linearly with increasing logarithm of the interaction modulus, a measure of in situ extensibility measured in a pullout box. The reduction in working platform thickness attained with reinforcement was also larger when the target total deflection was smaller.