Soil–Water Characteristic Curves for Soils Stabilized with Class C Fly Ash

Abstract

Low-volume roads are often constructed with untreated or lightly treated gravels as the surface or base, and these materials are sensitive to moisture variation. The proper design of low-volume roads requires determining the effects of moisture variation on soil behaviors. A soil–water characteristic curve (SWCC) that characterizes the relationship between the degree of saturation and suction is an important tool for quantifying the mechanical properties of unsaturated soils. The increased use of additives to improve the engineering properties of marginal soils in pavement design has necessitated the need for rapid methods to quantify the SWCC of stabilized soils. This study used the dewpoint method for quick measurement of suction values at various water contents for silt and clay soils stabilized with Class C fly ash. The results indicate that significant suction could exist in soils stabilized with fly ash and that the suction values are greatly affected by the degree of saturation. The suction and degree of saturation in stabilized soils play a significant role in the strength of the stabilized material. The material stabilized with fly ash exhibited hysteresis on the SWCC. The data were also used to compare the suitability and efficiency of five predictive models. It was found that the Fredlund and Xing and van Genuchten models fit the curves for stabilized soils very well as compared with the simplified van Genuchten, Campbell, and Brutsaert models. It is recommended that the Fredlund and Xing and van Genuchten models be included in the Guide for Mechanistic–Empirical Design of New and Rehabilitated Pavement Structures.