Sinkholes form in driveways when underground moisture wears away the gravel foundation underneath, causing the pavement to sink into the cavity. As the hole expands, damage to the pavement and the resources required to repair it will increase. Fixing a sinkhole entails pumping grout into the hole to raise the driveway and replace the missing foundation.
Mark three drill holes with chalk in a triangle over the sunken area. Each hole should be at least 12 inches in from the edge of the driveway and evenly spaced 3 to 8 feet apart, depending on the size of the sunken area and the thickness of the driveway slab.
Attach a 1 1/2 inch bit to a core drill and drill the three holes through the slab.
Thread a hose into the lowest hole with a 1 1/2 inch nozzle. Screw the other end to a slabjacking pump.
Fill slabjacking grout into the pump with a scooper. This mix will contain sand, cement and water and special additives so the material won’t shrink when temperatures drop.
Turn the machine to ‘On’ and pump grout until the cavity beneath is filled. Move the hose to the next hole. Repeat this process until the cavity beneath each hole is filled.
Return the hose to the first hole and continue pumping grout until the pavement rises about 1 inch. Now that the cavity is filled, the pump pressurizes the grout in order to raise concrete hydraulically.
Repeat this process with each hole until the sunken area is level with the rest of the driveway. Wipe off grout from the hole with a moist cloth.
Pack stiff mortar into the holes with a putty knife, tamping it down as you go. Cut the top of the patch so its level with the driveway.
Block off the driveway for three days to allow the grout to harden completely before vehicles drive over it.