Effect of water content and density on strength and deformation behavior of clay soils

The objective of this research was to investigate the effect of varying density and water content on the strength and deformation behavior of a low, a medium, and a high plasticity clay, as well as to determine the water content at which transition from brittle to plastic behavior occurs for each clay type. We used the standard Proctor test to compact six samples each of low, medium, and high plasticity clays to establish the compaction curves. We failed the compacted samples under unconfined compression and visually inspected their brittle versus plastic behavior during compression. Additionally, we performed direct shear tests on three samples of each type of clay that were compacted at different water contents. We used the stress-strain plots from both tests to determine the transition water content between brittle and plastic behavior for each type of clay. The results showed that unconfined compressive strength first increased and then decreased with increasing water content, with the change in trend occurring within 5% of OWC for each type of clay. The high plasticity clay had the highest cohesion while the low plasticity clay had the highest friction angle. The transition between brittle and plastic behavior for the low, medium, and high plasticity clays occurred between 19-20%, 27-29%, and 30-32% water contents, respectively. These results demonstrate that, in areas where clay embankments may be subject to cracking due to seismic activity or excessive differential settlement, they should be compacted on the wet side of the transition water content marking the boundary between brittle and plastic deformation.