Experimental and Numerical Studies of Geosynthetic-reinforced Clays and Silts under Environmental induced Swelling

Abstract

Current design guidelines for reinforced soil walls and slopes recommend the use of granular soils such as gravels and sands as select fills. Cost savings could potentially be realized by using on-site clays and silts. Some clays are swelling and silts are frost susceptible. When considering the use of swelling clays and frost susceptible silts as fills, environmental loading due to swelling-shrinkage and freeze-thaw effects from environmental changes could become a design issue.

To examine the hypothesis that consideration of environmental loading during design will produce improvements in the performance of geosynthetic-reinforced soil structures that use clays or silts as fill materials, experimental and numerical studies were undertaken. Geosynthetic-reinforced clay specimens were subjected to wetting and drying in a model test apparatus developed and commissioned for this study. In separate test set-up, reinforced silt specimens were subjected to freezing and thawing. Tests on unreinforced specimens were also performed in otherwise identical conditions for comparison purposes. Movements of the specimens, soil strains, reinforcement strains, soil suctions and soil temperatures were monitored during the application of environmental loading in addition to mechanical loading from external stresses.

The results of the laboratory model tests showed that reinforcements reduced horizontal displacements of the clay specimens during wetting and drying. The same is true for the case of silt during freezing and thawing. The environmental loading induced strains, and therefore stresses in the reinforcements. The measured geogrid strain during the wetting-drying of reinforced clay specimen was up to 0.75%. Similarly, the measured geogrid strain in the reinforced silt specimen during freezing-thawing cycles was up to 0.57%. The strains were greater than the strains generated by mechanical loading for the range of applied stresses used in this study.

Numerical models were developed to simulate wetting only induced swelling of reinforced clays and freezing only induced expansion of reinforced silts specimens. They were used to simulate the results of laboratory model tests. The performance of geosynthetic-reinforced soil slopes with swelling clay fills and frost susceptible silt fills was evaluated. Parametric studies were performed to determine important parameters affecting the performance of reinforced clay and silt slopes.