Types of Jet Grouting Injection Methods for Stabilization and Improvement

According to the desired geometry of the stabilization zone, three types of jet grouting injection systems are commonly used, as schematically shown in Figure 1:

  • Single Jet Injection

  • Double Jet Injection

  • Triple Jet Injection

🔹 Single Jet Injection System (S)

The single jet system is the simplest form of jet grouting used for stabilization, soil improvement, and nailing. In this method, only grout slurry is injected to erode and mix with the surrounding soil.

In certain soil conditions, especially those with sticky or cohesive residues, air pressure may be necessary to transport the spoil to the surface. Without air, surface heave may occur, which can pose serious risks, particularly if grouting is performed beneath an existing structure.

When there is a risk of ground heaving, it is critical to ensure complete removal of soil spoil from the boreholes. Additionally, under groundwater conditions, erosion efficiency significantly decreases without air, which leads to increased cutting energy requirements.

🔹 Double Jet Grouting System (D)

The double jet system adds compressed air to surround the grout jet, enhancing erosion, particularly below the water table.

However, a significant percentage of the grout may be wasted due to airlift suction, which pulls the slurry back to the surface. Despite this, the double jet method has proven highly effective in coarse-grained, non-cohesive soils such as sand and gravel.

🔹 Triple Jet Grouting System (T)

The triple jet grouting system uses three fluids: grout slurry, high-pressure water, and compressed air (surrounding the water jet). The system is equipped with a nozzle below the water jet that helps carry the excavated soil to the surface, while partially limiting the slurry injection.

In the double jet system, erosion is controlled by adjusting the water-cement ratio. In contrast, in the triple system, erosion is independent of the grout slurry, optimizing the efficiency of the injection process.

This decoupling allowed the cement content to be adjusted independently of the cutting energy, offering a significant advantage. In double jet systems, the soil had to be mechanically cut first, adding a preparatory step.

🚧 Development and Evolution

By the 1980s, trust and field experience in jet grouting led to widespread use. Since the early 1990s, newer jet injection methods enabled larger treatment radii and significantly increased column diameters.

These innovations made it possible to construct columns exceeding 5 meters in diameter, and even up to 9 meters in softer soils (Figures 2 & 3). This resulted in up to 20 times more treated volume compared to previous systems, thanks to advanced equipment, higher flow rates, and increased pressures.