There are internal modifiers like lime and Portland cement and external modifiers like various types of geotextiles that get installed over the soil for surface stability or can be added internally for added shear strength and reinforcing.
Lime stabilization works well with clay and more plastic soils that either are or can become too wet for ideal support. The calcium in the lime will replace higher reactive cations in the soil structure and make the soil particles to have less attraction to water.
Lime stabilized soil will reduce the dry density of the soil but will increase the bearing ratio of the soil even in its saturated state. Typical additions of lime would be 3 to 5 percent. Lime also has a drying effect on soils with less clay but you do not get the benefit of a chemical reaction.
Clay soils can be improved by adding lime. Hydrated lime is the best source of free radicals to make the transition.
Silty Loam can be improved by addition of pozzolans. These include fly ash, aluminum silicate and calcified shale.
Sandy formations can be improved by removal and mixing with Portland cement, aggregate and water in a stand up or drum type mixer.
The type of soils encountered in the soils report and the final use of the developed land will play an important part in what can be done to improve site conditions. The best sites have in-situ soils which can be combined across the development to minimize delivery of materials from outside the project. Source: Civil Engineer, Site Development for over 25 years