Remediation Techniques
Grouting and Underpinning are the techniques used by licensed contractors in the Sinkhole Repair Process.

• Grouting

The discovered sinkhole activity can be remediated by the injection of grout into the sinkhole activity zones.

The identified sinkhole activity zones can be remediated by injecting a low to moderate slump cementicious grout, under pressure, into the subsurface. The purpose of the grout injection program is to grout within and along the top surface of the limestone about the affected area to restrict and/or seal breaches in the surface of the limestone (where evident) that connect the soils that overlie the rock surface to suspected cavernous bedrock zones, thereby reducing the potential for future subsoil raveling and migration. In addition, the grouting may serve to compress and reinforce the subsidence of the overlying undisturbed soil zones into the weak zones.

The grout materials will consist of a combination of Portland cement, fine aggregate and water. Additives may be used, provided the grout mixture meets slump requirements. Hydro-active and micro-fine grouts are acceptable. For filling grouting of voids and cavities and compaction of surrounding sands, using conventional cementicious grout, the grout mix will have a target slump of 3 inches, with a plus or minus 1-inch tolerance in the field, as measured at the truck. The grout mix design shall have a 28-day compressive strength of at least 300 psi, or more.

• Underpinning

Underpinning is a stabilization technique used to stabilize the property. Pin piles are drilled down to the bedrock and used to support any unstable part of the property. In certain grouting programs it is recommended that the property have underpins installed prior to grouting to minimize the chance of any further structure damage caused to the property from the grout displacing any extremely weak subsurface material.