Jet grouting is a method of ground reinforcement that unlike classical forms of grouting that permeate through the soil uses high kinetic energy in the form of a high velocity jet of grout to breakdown the soil structure and simultaneously mix cement grout with the in-situ soil.
Why do we use Jet Grouting
To increase soil strength and reduce ground deformation, reduce soil permeability and to treat the ground, when other methods of grouting simply are unsuitable.
Advantages of Jet Grouting
The distinct advantage of jet grouting is that it can be effective in all types of soil, unlike classical grouting techniques, which rely on permeation through the voids in the soil mass. Jet Grouting can be used in ground retaining systems, cut-off barriers, base plugs of shafts, tunnelling, underpinning and to create rigid inclusions.
How does it work?
1. Implementation and methods
The equipment consists of a stationary grout production plant (silos, grout mixer, high pressure pump) that is connected to a drilling rig with high pressure grout lines. The drill bit is equipped with injection nozzles whose characteristics depend on the type of soil and on the shape, size and strength of the anticipated column or element.
The following steps are carried out at each injection point;
- The rig is positioned at the drilling location;
- A small diameter (70 to 120 mm) hole is drilled through the layer of soil requiring treatment;
- Grout is pumped through the rod with a very high flow (200 to 400 L/min) using a high pressure pump and exits through one or several small diameter injection nozzles (diameter 1 to 10 mm) that are installed on a monitor at the tip of the drilling rod;
- Slow withdrawal of the tool with full rotation of the drilling rod for column formation and partial rotation for panel formation.
2. Jet Grouting Methods
There are three jet grouting methods. Selection of the most appropriate method is generally determined by the soil conditions, the geometry of the element to be constructed and the application;
3. Characteristics of Jet Grouting
The characteristics (columns diameters, length of the panels, composition of the mix, permeability, compression strength etc) of the jet grouting elements depend on the treatment parameters (extraction speed, rotation speed, grout injection pressure, flow and density etc), the soil conditions (type of soil, grain size distribution, compaction etc) and on construction method (mono, double or triple-jet).
Jet Grouting has a very wide range of application;
- Ground improvement under uniform loading (heavy storage platforms, embankments, quays, slabs) or under localised loads (building footings, bridge piers). A load transfer platform (LTP) is usually required above the jet grouting columns;
- Impervious cut-off walls and bottom plugs for deep excavations can be formed with jet grouted elements. This technique is particularly suitable for deep shaft construction below ground water level or near sensitive structure;
- Retaining walls using secant Jet-grout columns designed as gravity walls or cantilever walls. Steel reinforcement can be inserted in the Jet Grouting columns as required (lube, rebars, cages);
- Underpinning (settlement mitigation, excavation of additional underground floors below existing building, excavation along existing structures);
- Tunnel canopy structures;
- Reinforcement of soils where existing utility lines and buried structures are present;
- Projects with limited headroom or in cramped spaces.