| This dissertation presents an investigation of the potential use of geosynthetic reinforcement as a remedial measure for shallow slides in earth embankments constructed of highly plastic clays. Such earth embankments are stable during construction but become unstable 10 to 30 years after construction. For geosynthetic reinforcement to be effective as a remedial measure, significant forces must be mobilized in the reinforcement.; Finite element computations were performed using a range of soil types and embankment geometry to investigate the magnitude of horizontal strains in unreinforced embankments, which are stable during construction. Reinforcement forces during construction were estimated using the computed horizontal strains. Results from these computations showed that for high PI soils and embankment geometries like those encountered along Texas highways, the horizontal strains, and thus the mobilized forces were very small during construction.; Additional finite element analyses were performed to simulate post-construction conditions in both unreinforced and reinforced embankments. Triaxial compression tests were performed with a "constant shear stress" (CSS) stress path that is believed to represent the field stress path to validate the constitutive model used in the finite element analyses. The failure envelope obtained from these tests was found to be significantly different from the failure envelope obtained using conventional triaxial compression tests where the axial load in increased to failure. In addition, these tests showed that very little deformations take place prior to failure in the laboratory specimens. The finite element analyses showed that the mobilized forces in the reinforcement after construction were still small, but the reinforced embankments were stable. Conventional limit equilibrium slope stability analyses were performed using mobilized forces computed from the finite element analyses to evaluate the role of the reinforcement in increasing the factor of safety. Results from these analyses showed that the factor of safety was less than one for stable embankments. Further investigations revealed that the effective normal stresses computed from the finite element analyses were much higher than those from limit equilibrium analyses. These high effective normal stresses caused an increase in shear strength, and helped stabilizing the slopes even though deformations in the reinforcement were small. |
