Compaction Grouting
Is a highly effective ground improvement technique of injecting a very stiff yet pumpable grout mixture into the soil to improve bearing capacity. This is accomplished by using a very high pressure to expand a bulb of very low slump grout through an injection pipe. The expanding mass of grout compacts the soil around each point that it is discharged.
Compaction grouting techniques are often times used for pre-construction site improvement, stabilize soil in low bearing soil, level slabs and sometimes even rectifiy sinkholes.
Typically it is done in stages, the first would be installation of injection pipes to the bottom of the zone being densified. The pipes are either drilled or driven into place. The injection pipe is then opened up at the bottom in order for the grout to be pumped. Using a very high pressure pump, a specially designed low volume grout is pumped through. This is where the stabilizing happens as the grout expands in a bulb, the radial force exerted compacts the surrounding soils. A relatively slow injection rate is used to prevent fracturing the soils, allowing water to dissipate and thereby reduce uplift. Injection continues until either refusal pressure is attained or heaving occurs at the surface. Grout placement continues at shallower elevations as the injection pipe is withdrawn in stages as shown above.