Compaction Grouting (also known as Pressure Grouting) involves the use of low slump, mortar-type grout pumped under pressure to densify loose and/or liquefiable soils by a cavity displacement action. Compaction grouting injection casing is typically installed by drilling or driving steel pipes of 2-inch ID or greater. Injection of the stiff, 3-inch or less slump, cement grout is accomplished under pressures generally ranging from 100 to 400 psi. Refusal pressures of 400 to 600 psi are common in most granular soil projects where liquefaction is the concern. Grout pipes are installed in a grid pattern that usually ranges from 5 to 9 feet between locations. Grouting volumes can typically range from 3 to 12 percent of the treated soil volume in granular soils, although volumes up to 20 percent have been reported for extremely loose sands or silty soils. Compaction grouting is not very effective in situations where the overburden is less than about 8 to 10 feet (800 psf). Grouting can be accomplished for new construction or as retrofit from inside existing facilities.