What Is Compaction Grouting?

Compaction grouting is the controlled injection of low-slump, low-mobility, soil/cement grout into the subsurface soils. The intent of the grouting program is to compact loose, coarse-grained soils and displace and/or densify fine-grained soils.

How Does Compaction Grouting Work?

Because compaction grout is viscous, it does not travel far from the point of injection, even in very loose or weak soils. Rather, a homogeneous grout ‘bulb,’ typically up to 6 feet in diameter, is formed around the injection point, displacing the soil radially.

In deeper soils, the bottom-up method is the most common form of compaction grouting. Grout bulb formation commences at the lowest point of the targeted soil zone. Raising of the grout pipe and further grouting cycles at finite intervals results in the continuous formation of a grout bulb ‘column’ through the treatment depth. Overburden depths on the order of 3 - 6 feet are usually required to contain the grout at depth and maximize densification.

In shallow soils (less than 6 feet), where overburden pressure is insufficient for adequate soil densification, the process can be reversed in order to artificially create the overburden stress required to contain pressure at the lower levels. In this top-down technique, grouting begins at the top of the treatment zone. Once the initial grout bulb has cured, it is drilled through to allow the grout pipe to be advanced to the next stage. The grouting and drilling process is repeated to the bottom of the target zone.

In both techniques, strategic, grid-based grout column construction, typically performed from the outside of the work area in, forces the displaced soil particles into a tighter configuration, thus improving soil strength and bearing capacity.

What Soils Are Appropriate For Compaction Grouting?

Compaction grouting can be accomplished in almost any type of soil. However, the degree of improvement is contingent on the subsurface conditions. Clay soils are usually more difficult to compact, however, they can be compacted if the proper pump rate and mix design are utilized.

What Are the Advantages of a CGS Compaction Grouting Solution?

Compaction grouting offers a very cost effective alternate to deep foundation systems or conventional underpinning methods. The grouting process produces very little disruption to the surface and vibration-sensative structures.

It can readily be accomplished under low headroom/restricted access conditions, often without disrupting normal facility operations. Compaction grout is non-toxic, and grouting activities have minimal impact on the surrounding physical environment. Since little material is wasted, as low slump-grout is accurately targeted underground, the results are highly effective. CGS batches its own grout on site, ensuring the optimum grout mix for the project.