Jet grouting is a ground reinforcement technique. One or several jets of fluid with high kinetic energy are used to break apart and mix the ground with a liquid cement slurry so as to form a column of “soil concrete”.
Presentation and key elements
What is jet grouting and why do we use it?
Jet grouting is a soil reinforcement technique. It is used as a targeted treatment for a wide range of applications: control and reduce settlement under structures, increase of bearing capacity, create impervious cut-off wall or impervious bottom for deep excavation, install retaining walls, underpin existing structures, reinforce soils with existing utilities lines and burred structures, operate in areas that are difficult to access (limited headroom, cramped spaces, etc.).
Basic principle of jet grouting
Jet grouting improves the mechanical characteristics of the soil using a fluid jetting with very high kinetic energy that breaks up the soil structure and mixes the soil particles in-situ with a grout to create a homogeneous mass of high strength reinforced soil-cement material.
Depending on the overall design and soil conditions, several methods of treatment have been developed (single or double curtain wall, secant columns walls, plugs, isolated columns, etc.) making of jet grouting a flexible technique.
Execution of jet grouting
The equipment consists in a fixed grout production plant (silos, grout mixer, high pressure pump…) attached to a drilling rig with high pressure grout lines. Once in place, the rig drills a small diameter hole (70 to 120 mm) through the layer of soil requiring treatment. Grout (which is often a cement slurry) is then pumped through the rod with a very high flow (200 to 400 L/min) and high velocity using a high-pressure pump and exits through one or several small diameter injection nozzles (1 to 10 mm). The tool is then withdrawn to form column (with rod rotation) or panel (with no rod rotation).
As a rule, jet grouting suits poorly to soils with blocks and rough gravel, to organic materials. It is not adapted either to soils through which large volumes of water flow.