| Compacted clay soils are commonly used as hydraulic barriers in waste containment systems such as in liners and covers for landfills, impoundments, reservoirs, and ponds. Compacted clays can minimize infiltration of fluid into waste or control the release of contaminated fluids to the surrounding soils and groundwater. The hydraulic properties of these soil-based structures can be adversely affected by desiccation cracking. The presence of cracks in the soil matrix increases significantly the soil hydraulic conductivity while decreasing the strength of the soil. Conditions for crack formation are most favorable during the construction of the clay liners. Factors promoting crack formation during construction include exposed lift interfaces, movement of heavy construction equipment, and differential settlements. Cracking may also occur as a result of consolidation effects. The addition of waste above the liner causes it to consolidate, which decreases the ductility, increases the stiffness of the clay liner and, thus, produces cracks.; Previous studies evaluated the use of soil additives (such as lime, cement, and sand) as a crack reducing mechanism. Initial results indicated that soil shrinkage was reduced. However, in many cases the additives resulted in an increased hydraulic conductivity and decrease in soil plasticity. As a result, there is an increasing interest in the use of fiber reinforcement, which has shown successful results in concrete and other material applications. The present investigation studied the potential for fiber reinforcement to decrease a soil's crack potential while also improving the hydraulic performance of the clay material.; Results of the study provide information on the use of polypropylene fibers mixed with clay soils of varying plasticities. The percent of fiber is varied, and the test results are analyzed to search for the mix proportions that lead to an "optimal" soil-fiber mix. The optimal soil mix is selected for additional testing to provide information on the cracking properties of natural clay soil liners versus the clay liners reinforced with the "optimal" proportion of fibers.; Fiber inclusion enhanced the tensile strength of the fiber-soil composite. This investigation developed a model to assess the increase in tensile strength. The model describes this increase in terms of fiber properties, soil properties, and fiber/soil interface parameters. The sensitivity analyses indicated that fiber content and soil moisture content were among those parameters that had the most impact on the model outcome. |
