OPTIMUM MOISTURE-CONTENT FOR DYNAMIC COMPACTION OF COLLAPSIBLE SOILS

The influence of moisture content on dynamic compaction efficiency was evaluated at six field test cells, each with a progressively higher a verage moisture content. The soil profile consisted of collapsible san dy silt, and average test cell moisture contents ranged from 6% to 20% . At each cell, compaction was performed with a 4.54 t weight dropped from a height of 24.3 m. Compaction efficiency was evaluated using (1) crater depth measurements, (2) cone penetration tests before and afte r compaction, and (3) undisturbed samples before and after compaction. Crater depth increased by a factor of 4 as moisture content increased . The degree of improvement increased up to a moisture content of abou t 17% and then decreased. The optimum moisture content and the maximum dry unit weight are similar to those predicted by laboratory Proctor testing using energy levels comparable to those employed in the field. Maximum dry unit weight decreased with depth, while optimum moisture content increased before the compactive energy decreased with depth be low the impact point.