Compaction or permeation grouting is mainly used for sinkholes and settling foundations.
Compaction grouting is a method where fast-setting polyurethane foam is injected into loose soil. The foam expands, forming balls or columns of dense structural foam. The expansion compacts the surrounding soils and increases the load-bearing capacity.
Permeation grouting is how contractors can turn loose soil into a dense solid mass beneath a structure, under a roadway, around a leaking pipe, or near a seawall increasing strength, stiffness, and reducing permeability (the state or quality of a material or membrane that causes it to allow liquids or gases to pass through it). This helps with soil instability in areas like coastal regions.