The compaction, compressibility, and shear strength behavior of an alum sludge both untreated and treated with additives are presented. The significance of the sludge behavior in terms of landfill/embankment design and construction is discussed. The additives used were a slake lime, a fly ash, and a local clay sand; the additive content was 60% by dry weight of sludge. The standard Proctor comparative effort and the conventional consolidation test were used for testing. The shear strength was determined using both the laboratory fall cone penetration test and the consolidated undrained triaxial compression test with pore pressure measurements. The moisture-density relation is not that of the typical one-hump curve. Instead, the dry density decreases with increasing water content from a maximum near zero water content. The additives appear to have an insignificant effect on the compaction curve. However, the additives improve the plasticity, compressibility, and shear strength behavior considerably. The untreated sludge has a high effective angle of internal friction, but the undrained shear strength is low, especially at high water content. Both the untreated and treated sludges are sensitive and highly thixotropic. It is concluded that admixture stabilization is an effective method of improving sludge properties for easier handling and also for increasing the volume of disposed sludge. Although the stabilized sludge within the range of conditions investigated is still too compressible and without sufficient shear strength for embankment construction, the potential for use of stabilized sludge as an embankment material can be enhanced through further dewatering or raising additive content or both.