Unstable soils cause problems for those trying to build housing structures on top of them. Soils that are too wet or spongy can cause major damage to housing infrastructure. The addition of lime to unstable soil is an effective method of changing the soil's composition, making it suitable for construction.
Lime is effective in drying wet patches of soil for immediate construction. Quicklime chemically bonds with soil, creating heat, which dries away excess water. When clay is present in the soil, lime reacts further, bonding with the clay and increasing the moisture-holding ability of the soil. Drying of large patches of soil may take as short as a few hours.
Lime affects clay by making it easier to crumble, which also makes it easier to handle. Calcium ions from the lime move to the surface of the clay, pushing away moisture, making the clay granular. One to 4 percent of a soil's dry mass replaced by lime is enough to permanently effect clay soil.
Lime modification, which changes the pH levels of a soil, is not a permanent change. Lime stabilization, however, permanently stabilizes clay soils. Lime will reduce the shrinkage and swelling of clay as well as increasing its weight bearing capabilities, making it suitable for heavy concrete and weight bearing structures.
Lime is spread by tractor equipment, or spreader trucks, that spray lime a the rate of 5 percent to the surrounding soil area. Water is added to the soil to aid the absorption of the lime into the area. A rotary mixer, like a rototiller, mixes the soil and lime together. Lime is mixed to a depth of 16 inches. A motor grader is run over the area to shape the soil appropriately for building.
Cost for lime stabilization is lower than many other bracing methods for unstable areas. A depth of 16 inches of lime modification is around $5 per square yard, as opposed to undercutting an area, which costs around $17 a square yard.