Estimating Variation in Stiffness and Volume Change of Clays from Geochemical and Index Properties

Clayey soils from six different locations in Texas were analyzed and evaluated with respect to their expansion and shrinkage and change in stiffness associated with moisture content variation. These soils consist of five high plasticity-index (PI) clays (PI greater than 25) and one low-PI clay (PI = 17). The behavior of the clays changes dramatically with moisture content fluctuation, thus causing stiffness and volume changes throughout the year. Total or differential volume movements caused by swell or shrinkage strains of expansive soils and reduction in modulus can exert enough pressure to damage the pavements and cause maintenance problems. The intent of this research project is to develop mathematical models capable of predicting the behavior of clays under different moisture conditioning processes. The variations in modulus and lateral and vertical strains were evaluated under three different moisture conditioning processes. In the first process, called Dry-from-Optimum (DFO), specimens were compacted at their corresponding optimum moisture contents and then subjected to drying. In the second process, Saturated-from-Optimum (SFO), specimens prepared at their optimum moisture contents were subjected to saturation. The third process, Dry-from-Saturated (DFS), consisted of moisture conditioning specimens prepared at their corresponding optimum moisture contents to saturation first and then drying the saturated specimens. The proposed models are based on two sets of geotechnical parameters of soils: index parameters and chemical-mineralogical parameters. The models were validated with one set of data not used in the development of the models. Comparison between the model predictions and the measured data show that these models are able to reproduce the main features of stiffness and volume changes due soil moisture fluctuations. The developed models can be implemented in the assessment of the pavement performance of pavements subjected to moisture fluctuations