Compaction grouting is another method of improving the bearing capacity of soil by soil displacement method. It involves high-pressure injection of a very stiff homogeneous grout mix of slump in the range of 25mm, at low injection rates (< 2 cubic feet/minute) to subsurface locations in order to displace and compact the soils.

 

Once the desired location and depth of sub-surface is identified, injection pipes are installed into soil. The pipes are driven, jetted, or drilled to the bottom of the zone requiring improvement. A low volume and low slump grout paste is injected at high-pressure with constant low pumping rates. The grouting method is carried out in a manner to form a bulb shape exerting radial forces in all directions as it displaces and compacts the adjacent soil. The low pumping rate is employed to prevent both soil fracturing and uplift by allowing excess water to dissipate. Injection continues until a pre-determined refusal pressure is reached or uplift occurs at the surface. The process of grouting and formation of bulb shape grout is continued until it reaches the surface.

 

One important factor that is to be considered during the grouting exercise is to ensure the pressure being applied in the substrate is not causing any uplift or heaving. The most suitable type of soils where this method is found to be effective is fine-grained soil with sufficient permeability that allows excess water to flow and dissipate. Depending on the type of soil, the effective radius of an injection hole also varies