Jet Grouting – Development History and Technology

Introduction

In construction and civil engineering projects, soil is a critical factor—yet many people are unaware of its importance. The load from a structure is transferred to the soil through the foundation. If the underlying soil cannot bear the load or undergoes settlement, the structure may become unserviceable, potentially resulting in human casualties and financial losses. For example, the 1997 Thredbo landslide in Australia caused 80 fatalities and millions of dollars in damages to the local ski resort.

One of the methods used to stabilize the ground and reinforce weak soils is jet grouting, also known as high-pressure grouting.

Given urban development plans and specific geographic or site conditions, it is sometimes impossible to avoid problematic soils. In such cases, geotechnical engineers must improve soil conditions. Jet grouting is among the most effective soil improvement methods.

What is Jet Grouting?

Jet grouting involves injecting high-pressure cement grout into the soil, displacing water and air within the voids and among soil particles. This process improves the soil’s strength and durability while reducing its permeability. The procedure starts with drilling to the target depth, followed by high-pressure injection to create soil-cement columns.
Figure 1 illustrates the jet grouting process.

History of Jet Grouting

The concept of jet grouting originated in Japan during the 1960s with the use of high-pressure water to inject cement grout into the ground. Early implementations often produced irregular soil-cement columns and inconsistent strength improvements. Over time, research and technological advancements resolved these issues, leading to two main techniques:

• Chemical Churning Pile (CCP):
  Cement grout is injected under pressure through the nozzle at the tip of the drilling rod.

• Column Jet Grout (CJP):
  First, soil particles are loosened by high-pressure air and water, then cement grout is injected under high pressure.

Japan began using this method extensively in the 1970s for soil improvement and settlement control. After its success, other countries such as Germany, Italy, France, and Singapore adopted it. In the 1980s, the technique gained attention in Europe after it was proposed for stabilizing the Leaning Tower of Pisa in Italy. Today, jet grouting is globally recognized as one of the most effective soil improvement technologies.

Jet Grouting Evolution Over Time

Jet grouting is considered one of the most complex and technically advanced grouting techniques. Although it is less dependent on in-situ soil properties, local soil conditions still play a crucial role in selecting execution methods and achieving desired soil-cement column results.

This technology was introduced in the United States in the early 1980s and gradually gained traction in the engineering community. It has effectively treated various soil types for diverse applications. In recent decades, many specialized contractors have enhanced this system, employing single-fluid, double-fluid, and triple-fluid technologies.

Recently, the Super Jet system—a development in double-fluid technology—has been introduced. It offers cost-effective performance and enhances soil improvement capabilities.
Figure 2 shows the technological progression of jet grouting from its inception in the 1970s to the introduction of Super Jet systems post-2000.

Jet Grouting Systems: Single, Double, and Triple Fluid

Single-Fluid System

This is the simplest form of jet grouting. Grout is pumped through an injection rod and expelled at high speed through horizontal nozzles in the monitor. The high-energy jet erodes the soil structure and replaces it with a grout-soil mixture. This method is most effective in non-cohesive soils.

Double-Fluid System

This system simultaneously injects grout within a cone of compressed air. It can create larger columns than the single-fluid system and performs better in cohesive soils.

Triple-Fluid System

The most advanced of the three, this system involves the simultaneous injection of air, water, and grout through separate nozzles. Grout is injected at a lower speed, separating the soil erosion process from the grouting phase. This results in higher-quality soil-cement mixing.
Figure 3 illustrates the operation of these systems.

Applications of Jet Grouting

Jet grouting serves various functions, depending on project needs. Key applications include:

1. Improving Mechanical Properties of Soil

High-pressure grout fills the voids between soil particles. Cement in the grout acts like binder in concrete, bonding the particles and enhancing strength and shear resistance.

2. Reducing Permeability

Jet grouting creates barriers that reduce soil permeability and prevent water seepage. It is often used in high groundwater areas and dam construction for constructing cut-off walls.

3. Settlement Control

Jet grouting is used to correct or control settlement. For example, it helps stabilize buildings experiencing settlement or when tunneling occurs beneath structures.

Conclusion

Jet grouting is a highly advanced and effective technology in geotechnical engineering. By offering innovative and reliable solutions, it has played a vital role in strengthening weak soils. With the ongoing advancement of equipment and techniques, jet grouting has become a primary solution for complex engineering challenges. As research and innovation continue, its applications are expected to expand, cementing its position as an essential tool in civil and geotechnical engineering.