Subgrade Stabilization - Fly Ash vs Lime. What works best for what soil type?

Question

If anyone out there on answers works with roadway construction.... What has your experience been?

Answer 1

Both materials will work with pretty much anything short of pure mud. Lime will even stiffen up topsoil. The general consideration is which one is available in quantity close to the project, and cheapest. It should not be considered a substitute for engineered fill. This method is not generally preferred because it is difficult to acheive any uniformity of mixture on the jobsite. I can't imagine why anyone would want to dig up a large quantity of dirt and try to evenly mix in lime on a jobsite. I've never been that hard up for structural fill. It would be more cost effective to dig it out, and bring in new dirt. You may know that when placing and compacting engineered soils, the material must be proctored which establishes acceptable moisture content, lift thickness, and provides data as to how acceptable compaction may be measured. Changing the composition of the material changes this data therefore effecting optimum compaction. In my experience, if the unstable condition is due to improper placement or wet material, it must be removed and replaced with either clean crushed stone, or dry compaction fill. Generally dumping lime to tighten up a soft area is something done by shady contractors trying to get over on somebody, or by harry homeowner trying to save money.