Study of Problematic Silt Stabilization (05-2038)**
Bogdan George Barbu, Texas A&M Transportation Institute
Kenneth McManis, University of New Orleans

Soils with high silt content are a common occurrence and can raise widespread road construction and performance problems due to their low strength, minimal bearing capacity and highly moisture susceptibility. Their stability is greatly influenced by the degree of densification achieved during compaction. Problematic silts subjected to high compaction energies develop pumping phenomenon, especially when the soil is wet of optimum. The strength and stiffness of silty-subgrade soils is also greatly reduced when moisture infiltrates the compacted soil due to capillary action during post construction period. Moisture susceptibility is an important factor that affects the mechanical properties of subgrade materials. This paper presents a study regarding the identification and stabilization of problematic silts. The characteristics of a set of three soils with a high potential to pump are investigated. Conditions generating pumping phenomenon are duplicated in the laboratory by a set of cyclic triaxial tests. In addition to the high silt content, the plasticity character and moisture susceptibility are noted as significant factors for pumping. The potential for the stabilization of problematic silts with Portland cement and lime is also studied. The percentages of additives are considered based on strength criteria and the evolution of moisture susceptibility of the subgrade material is investigated using Tube Suction Test. The results demonstrate Portland cement represents the most effective chemical additive for the soils considered in this study. This paper demonstrates the relevance of moisture susceptibility criteria as an important consideration in the design specifications for subgrade stabilization.