Jet grouting is a ground improvement technique that enhances soil properties by injecting a high-velocity fluid jet.
At its core, jet grouting improves the mechanical characteristics of the soil using a fluid jetting with very high kinetic energy. This powerful jet serves two primary functions:
- Breaking Up Soil Structure: The high kinetic energy of the jet breaks down the existing soil matrix. This disaggregates the soil particles, preparing them for mixing.
- Mixing with Grout: Simultaneously, the jet injects a grout (typically a cementitious mixture) into the broken-up soil. This process happens in-situ, meaning it occurs directly within the ground.
The result of this forceful mixing is the creation of a homogeneous mass of high strength reinforced soil-cement material. The soil particles are intimately blended with the solidifying grout, forming a composite material that is significantly stronger and less permeable than the original soil.
The Jet Grouting Process
The process typically involves drilling a borehole and then withdrawing a monitor (a specialized rod with nozzles) while injecting the grout or other fluids under high pressure. The type of jet grouting depends on the fluid(s) used:
- Single Fluid System (Soilcrete): Uses a high-pressure grout jet (typically 400-600 bar) to erode, mix, and replace the soil.
- Double Fluid System: Uses a high-pressure grout jet surrounded by a shroud of compressed air. The air stabilizes the jet and increases its range, creating larger columns or panels.
- Triple Fluid System: Uses a high-pressure water jet shrouded by air to erode the soil first, followed by a lower-pressure grout jet from a separate nozzle to fill the eroded space. This system is often used in cohesive soils and can create the largest column diameters.
As the monitor is withdrawn and rotated, the jet cuts through the soil, creating cylindrical columns, panels, or blocks of the soil-cement material.
Benefits of Jet Grouting
Using this method offers several advantages for foundation and geotechnical applications:
- Improved Strength: Creates a much stronger ground mass capable of supporting heavier loads.
- Reduced Permeability: The soil-cement material forms a barrier that significantly reduces water flow.
- Versatility: Can be used in a wide range of soil types, from sands and silts to some clays and even soft rock.
- Targeted Treatment: Allows for precise treatment of specific soil layers or zones.
This technique is widely used for underpinning existing structures, constructing excavation support systems, sealing groundwater cutoffs, and stabilizing slopes.
