Jet Grout Technology Explained
Jet grout is a term for a very special technique used to construct tunnels and building foundations in water filled soils, as well as to to stabilize existing foundations in buildings.
Jet grouting blasts extremely high pressure fluids into the ground at ultra high velocities. The soil is broken up and mixed with the fluids to become one mass which then hardens. There are three basic jet grouting processes and three other terms commonly associated with jet grouting.
Monofluid Jet Grouting
A borehole is drilled to the desired founding level. Water, compressed air, and bentonite are used as a flushing medium to remove excess soils. The flushing ports are then closed and the binder nozzle begins to inject the binder into the soil at extremely high pressure, both disrupting and mixing the soil with the binder. While the binder is being sprayed, the drill begins to rotate backward slowly. As the binder sets, a homogeneous mixture is created.
Monofluid Jet Grouting is the simplest, cheapest, and easiest of the methods; therefore, it is the most common. It also provides a level of versatility the other methods do not. By using only one fluid to both break up the surrounding soils and set them, the drill bit is much less noisy and complicated.
Kajima or 3-Fluid Jet Grouting
With 3 Fluid Jet Grouting, the initial drilling process is the same, except that the hole which is drilled is much larger to accommodate a more complicated drill. Once the founding level is reached, a high powered water jet (70 Mpa) and compressed air blast into the soils, breaking up the surrounding area. The drill rod is slowly withdrawn and the binder is squirted into the displaced soils to make a homogeneous mass.
Due to using compressed air and water to break up the soils once the founding hole is drilled, tougher soils can be drilled into and fewer holes need to be drilled to cover the same area as with monofluid jet grouting.
Intermediate or 2-Fluid Jet Grouting
2 Fluid Jet Grouting is the intermediate version because it encompasses techniques of both Monofluid and 3 Fluid Jet Grouting to create greater efficiency with the simpler drill. By using the same tools as Monofluid Jet Grouting and adding the compressed air function to rotate around the drill bit, the diameter of the drilled hole can be slightly increased (up to 2 inches). Though the number may seem small, drilling fewer holes is more efficient and can save valuable time.
Permeation, Compaction, and Claquage Techniques
Though not formally jet grouting, permeation, compaction, and claquage techniques are sometimes used synonymously.
Permeation is a process whereby the binder (water/cement or resin/cement mixtures) is directly injected into a hole, without the soils being disrupted. The binder then permeates the soil by itself. Compaction uses a thick grout which is injected into loose soils physically lifting the soils. As the dense grout hardens, a denser soil structure is created. Claquage blasts soils at high pressures with a specialized tube. As the soils fracture, the cracks are filled with the grout to modify the soil structure and harden it.