Sulfates, sulfates and sulfates!!!
Lime treatemnt to modify soils is equivalent to drying a wet soil to an acceptable range and the long-term performance will be consistent with this. With the addition of quick lime, this will hydrate (the lime uses some of the water in the soil) and with the heat of hydration this will remove water from the soil(signifncnalty more than by hydration alone).
With increasing lime content, and where the pH is >12.4, the lime will start to break down the clay minerals and then with any additional lime it will begin to form calcium silicate hydrates and calcium alluminate hydrates (cements). Therefore as more lime is used the more likley you are to cement the soil (solidify if thinking about remediation of contaminants or stabilisation if just geotechnical).
Where lime alone cannot provide sufficient strength, then cement can be added. Where sulfates are present the use of GGBS or PFA can help.
If the Total Potential Sulfate is greater than 1.0%, DO NOT DO IT, you have been warned.
Modifying and stabilising soils will reduce consolidaiton and creep settlement of the fill.
Typical lime addition is up to 5%, and when mixed with cement you are probably looking at a ratio of 2:1 lime to cement.
Organic soils can be problematic, and normally you would not treat a soil with an organic content of more than 2%, but I have done human sewage with 60% organics using a combination of lime, cement, PFA and GGBS and engineered a general fill suitable for car-parking and areas of hard-standing.
All soils will need to be treated, so can involve large earthworks, although deep soil mixing is also possible, but you don't get the compaction of the fill in the same way as excavating and replacing.