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Of the types of soils that occur in nature, clay soils are the most physicochemically active. Their natural tendencies to change volume with moisture level changes cause billions of dollars of damage annually to transportation facilities. Methodologies to modify and stabilize their damaging behavior have been widely sought. In fact, there is evidence of clay soil stabilization in antiquity. Because these problematic soils are chemically active and their behavior can be improved through the application of chemical agents, a multitude of these agents have been applied. Some of these agents are naturally occurring, some are derived by manufacture, and some are the waste products of manufacturing processes. Why these clays are chemically active, how agents can be applied to improve the behavior of clays, and why the agents proposed should be evaluated are reviewed. Minimum requirements for adequate testing and evaluation are provided.

This paper describes the design, use, and results of a multiple leach-cell operation to test the changes in permeability and calcium removal of a lime-treated expansive clay under continuous water leaching. Seventy laboratory-prepared lime-treated clay specimens were subjected to continuous accelerated leaching for periods of 45 and 90 days with varying lime contents and compactive moisture contents. Permeability, leachate pH, and leachate cation changes were continuously recorded during the leach process. Results indicate that lime dramatically increased the soil's permeability, with maximum permeability occurring at the lime modification optimum (LMO). Leachate pH increased as the lime content of the soil increased but decreased linearly during the leach cycle. Calcium concentration in the leachate was lowest in specimens prepared at their LMO but increased as the lime content increased. There is strong evidence to suggest that calcium removal and permeability are in direct correlation to the complex ion interaction within the soil-lime mixture, and therefore the LMO is central in determining leaching effects on lime-treated soils.

Chemical stabilizing agents have been introduced that have performed in field applications to improve the behavior of earth materials. The same agents and materials subjected to standardized laboratory tests have often resulted in no improvement. For example, the tests often require pulverization of materials to finer states than are needed in the field or may require remolding when field applications are done in situ, as with injection applications. Some of the physical tests do not place treated materials in a situation resembling conditions in the field, yet they are applied to determine the use of these agents. The experiences of the author in developing performance-based testing of chemical stabilizers that better simulate field conditions are described. The situations include a physical erosion test to determine dispersion of clays that have been treated, two swell test preparation sequences simulating injection of chemicals into clays, a wet-dry test sample preparation using field gradation specifications, and a three-dimensional swell test for stability of treated clays when subjected to wetting. Also, the standardized physical test results that did not adequately represent behavior are discussed. The applications and indications of successful testing are reviewed. Possible development processes for performance-based tests, involving parameters of variance, are included for consideration.