Studies On Volume Change Movements In High PI Clays For Better Design Of Low Volume Pavements

Numerous low- to medium-volume roads such as Farm Market (FM) roads constructed on expansive clay subgrades, especially in the eastern and central Texas, encounter severe pavement cracking and premature loss of serviceability. The maintenance costs, in some cases, are greater than the initial construction costs. The roads built on problematic expansive soils often become distressed due to volume changes associated with seasonal moisture content fluctuations. This dissertation research was attempted to evaluate models that predict volume changes movements of
the expansive or highly plastic soils and also develop new models that could provide better prediction of volume change movements in expansive clays. In this research, laboratory investigations and field studies were conducted on soils from four different locations in which highly plastic and expansive clays were encountered. These sites were located in Fort Worth, San Antonio, Paris and Houston. Laboratory tests conducted included basic soil properties, chemical and clay mineralogy and engineering soil tests. All studied soils exhibited a high degree of volumetric expansion (more than 15%). Field monitoring programs composed of elevation surveys for various environmental conditions, soil moisture and soil suction monitoring, and identifying the new cracking in pavements at all four sites. Results showed the site environment conditions such as climate, large trees and drainage ditch have strong influence on expansive soil movements and pavement cracking. The details of the environmental effects including moisture conditions at which pavement cracks can be initiated are discussed. Finally, pavement elevation changes monitored from each sites were compared with various heave analytical type prediction models proposed by previous researches. In addition, a Finite Element Method (FEM) model with the incorporation of soil water characteristic data was used to predict heaving the test sections. Comparisons with measured data showed that the numerical FEM model predicted swell potentials close to the field monitored soil movements, explaining the significance and effectiveness of the numerical modeling of swelling behavior of unsaturated soils. Other regression correlations for improved predictions of soil movements are also included.