To effectively compact clay soil, what material should be added?

Lime is beneficial for effectively compacting clay soil due to its chemical properties that can alter the physical structure of the soil. When lime is added to clay, it reacts with the clay particles and aids in flocculation, which helps to reduce plasticity and improve the workability of the soil. This process results in a denser, more compact soil matrix. The addition of lime enhances the stability and strength of the clay, making it less susceptible to shrink-swell behavior and improving its overall load-bearing capacity.

In contrast, while sand can improve drainage and reduce the plasticity of clay, it may not provide the same level of compaction benefits as lime. Compost can improve organic content and soil fertility but does not necessarily assist in achieving effective compaction. Gypsum, while useful for improving soil structure and reducing compaction in some contexts, may not have the same impact on clay as lime does in terms of enhancing compaction and workability.