Is it really possible to strengthen the subsoil without digging up everything? Sure-just like jet grouting does. This high-tech activity uses high-pressure jets for subsurface mixing of soil and grout to develop firm columns without significant excavation.
In this article, we will analyse jet grouting itself, the working principle, where it is used and how it is transforming modern construction. This will be useful for anyone who wants to stabilise their foundation in a highly restricted area.
What is Jet Grouting?
Jet grouting has become an adaptable ground improvement method for strengthening and improving weak or troublesome soils. By injecting grout into the ground under high pressure, columns or blocks of solid ground are formed using a soil-cement mix. Within geotechnical engineering, it has many applications, including foundation underpinning, excavation support, groundwater control, and seismic rehabilitation under urban or restricted access conditions.
As compared to ordinary grouting, where voids are filled, jet grouting displaces and mixes in-situ soil, cementitious grout, creating a homogeneous and strong composite capable of sustaining heavy structural loads or acting as a barrier against groundwater.
How Does Jet Grouting Work?
Step 1: Drilling the Borehole
It starts with drilling a hole in the earth with a special drill equipped with a hollow rod. The drill rod is also equipped with nozzles, which are used to inject grout into the soil. It can reach the place that needs soil treatment at a certain depth. The drill penetrates the different soil layers it has planned, finally reaching the treatment level.
Step 2: Reaching Target Depth
In any method, whether it is decided to be a single, double, or triple fluid method, the machine is made ready for grouting after the target depth is attained. Thus, grout is linked to the system along with the other fluids (air, water), with thorough testing of the pressure and flow prior to injection.
Step 3: High-Pressure Injection Begins
A high-pressure jet of grout is injected through the nozzle. In the double or triple fluid methods, air or water is used to assist and is injected along with the grout through separate nozzles. This jet action breaks up the surrounding soil and mixes with it, forming a dense and hardened mass known as soilcrete.
Step 4: Rotation and Withdrawal of the Rod
As injection continues, the drill rod is rotated slowly and withdrawn upward. This will ensure that the grout fills every portion of the soil and creates a column from the bottom to the top. The column’s shape and size are controlled by withdrawal speed and rotation.
Step 5: Formation of Soilcrete Column
Then, as the grout is injected into the soil, it starts to set. The outcome is a concrete column of treated ground, which will bear the weight of construction or other loads. The resulting columns may be built up next to each other or may overlap to create walls, blocks, or slabs as required by design.
Step 6: Quality Control and Finishing
Once the grouting operation is done, the engineers measure the quality of the column using sampling techniques like coring or soil sampling. If the results give a good indication of the quality, the same procedure is repeated in the next location. All columns completed, the site is ready for construction or excavation.
Application of Jet Grouting
Jet grouting is particularly useful in the following applications:
- Foundation Underpinning: Strengthening foundations, especially those of heritage or sensitive structures, with respect to the existing foundations.
- Excavation Support: Creating temporary or permanent retaining structures for deep excavations.
- Water Cut-Off Walls: Preventing groundwater from entering the working area in tunnels or basements.
- Seismic Retrofitting: Raising shear strength and liquefaction resistance of loose soils in seismic zones.
- Tunnelling: Pre-treatment with jet grouting of the ground ahead of tunnelling operations to avoid any collapse and ingress of groundwater.
- Rail and Road Works: Stabilising embankments and supporting temporary works during upgrades.
Advantages of Jet Grouting
Jet grouting bears many benefits compared to normal ground improvement methods:
- Adaptability: Highly effective in all silt and soft clay types.
- Precision: Allows most localised targeted ground treatment with minimal disturbance to surrounding areas.
- Access Flexibility: Suitable for places with limited headroom or space.
- Structural Integration: Able to easily combine with existing foundations or support systems.
- Water Control: Very efficient for reducing permeability and groundwater control.
- Speed of Installation: Sometimes, faster than deep foundations or cut-off walls to set up.
Key Components of Jet Grouting
Grout Composition
Grouts are made up of a mixture of water, cement, and some necessary additives, such as bentonite or silica fume, which would modify certain properties, such as strength, setting time, or even permeability. The main criterion for the final grout mix is that it will be determined by project specifications and soil conditions.
Injection Parameters
Grout pressure (up to 600 bars), flow rate, angle of rotation of the driller rod, and withdrawal rate of critical injection parameters are strictly monitored and controlled; these are important for proper mixing and formation of a column and are injected into the soil.
Drill Rods
Hollow steel rods function as conduits for grouting to the desired depth; designed to withstand high-pressure injection, the rods have jetting nozzles at their tip.
Nozzles
Nozzles determine the angle and power of the grout jets; therefore, they are not only miniature but also highly powerful tools that carve and mix soil during the injection phase.
Types of Jet Grouting
1. Single fluid jet grouting
Single-fluid jet grouting uses only the injection of grout into the soil under very high pressure through a nozzle. Viscous grout transfer by pressure disrupts the soil, mixing and forming a solid column. This is more effective in loose sandy or silty soil, where the grout could easily penetrate. It is simple, economical, and easy to set up, but it is unsuitable for hard soils or clay-rich ones with small columns that are not as effective as the others.
2. Double Fluid Jet Grouting
Double-fluid-type jet grouting combines grouting and compressed air. The grout is injected through one nozzle, while the air is injected through another nozzle surrounding the first. The air assists in the spreading and sharpening of the grout jet for a better cut-and-mix soil action. Better performance is noted in soft medium clays and silty soil. The columns made in this method are larger and stronger than those made in the single fluid system. Although more equipment and setup are required, it is commonly employed in moderate soil conditions.
3. Triple Fluid Jet Grouting
In triple fluid jet grouting, water, air, and grout are injected separately through different nozzles. First, a high-pressure water jet cuts through the soil, while compressed air helps to loosen and displace it. Then, grout is injected into the loosened soil to form a strong and homogeneous soilcrete column. This is a very powerful system suitable for dense soils, gravel, and even weak rock. It can achieve large and strong columns and is excellent for difficult or critical projects. However, it’s also the most expensive and complex one. It generates more waste and needs skilled handling.
Conclusion
Jet grouting is the solution of choice today for every challenge of modern geotechnics. Its ability to improve ground conditions with great accuracy, even in confined and difficult soil types, makes it indeed the greatest reference for engineers across the continents. From a fully deteriorated foundation to deep excavation and groundwater barriers, jet grouting becomes a tailored solution effective for any of the problems at hand.