Jet Grouting

Jet grouting is a ground improvement method used in geotechnical engineering to improve the mechanical properties of soil or rock. It involves the creation of a cementitious soil-cement column or wall in the ground by injecting a high-velocity jet of fluid under high pressure.

The process of jet grouting involves drilling a small-diameter borehole into the ground and then inserting a grouting nozzle into the hole. The nozzle is then rotated and moved up and down in the soil while a high-pressure jet of grout is injected into the soil. As the grout is injected, the soil particles are eroded and mixed with the grout, forming a soil-cement mixture. The grout column or wall is then allowed to set and harden, producing a strong, stable structure.

Jet grouting can be used to improve soil properties such as strength, stiffness, and permeability, and can be used for a variety of applications including foundation support, slope stabilization, excavation support, and groundwater control. Jet grouting is often used in urban areas where access is limited or where traditional excavation and construction methods are not feasible.

The jet grouting technology is based on the high-velocity injection of one or more fluids (grout, air, water) into the subsoil. The fluids are injected through small-diameter nozzles placed on a pipe that, in its usual application, is first drilled into the soil and is then raised towards the ground surface during jetting. Alternative jetting procedures have been developed in time and will be presented in this chapter. In most cases, the jets propagate orthogonally to the drilling axis, inducing a complex mechanical phenomenon of soil remoulding and permeation, with partial soil removal. The injected water-cement (W-C) grout cures underground, eventually producing a body made of cemented soil. Most of the time, the treated volume has a quasi-cylindrical shape and is thus named ‘jet-grouted column’ or simply ‘jet column’. There is, however, the possibility to make cemented bodies of different shapes, either by changing the treatment procedure or by joining several partly overlapped columns.

 

Advantages and disadvantages of jet grouting

Jet grouting is a versatile and effective technique for treating soil or rock formations in geotechnical engineering. Some of the advantages of jet grouting include:

Ability to treat a wide range of soil and rock types: Jet grouting can be used to treat a variety of soil and rock types, including sands, silts, clays, and fractured rocks.

Ability to create columns of grout: Jet grouting can be used to create columns of grout that can support structures or improve the bearing capacity of the soil. These columns can be created in a wide range of diameters and lengths.

Minimal disruption to the surrounding area: Jet grouting is a relatively low-impact technique that can be performed with minimal disruption to the surrounding area. The equipment used for jet grouting is typically small and can be easily transported to the site.

Rapid installation: Jet grouting can be installed quickly, which can reduce project schedules and costs. In some cases, jet grouting can be installed in a matter of hours, which can be especially advantageous in emergency situations.

Ability to improve soil properties: Jet grouting can be used to improve the strength, stiffness, and permeability of soil formations. This can be especially useful in situations where the soil properties are not adequate for the desired application.

 

While jet grouting offers numerous advantages, there are also some potential disadvantages that should be considered when selecting a grouting technique. Some of the disadvantages of jet grouting include:

Limited depth: Jet grouting is typically limited to shallow depths, typically less than 30 meters. This is due to limitations in the equipment used for jet grouting and the need to maintain control over the grouting process.

Limited lateral extent: The lateral extent of jet grouting columns is typically limited to a few meters. This means that a large number of columns may be required to cover a large area, which can increase project costs.

Limited control over grout properties: Jet grouting can be more challenging to control than other grouting techniques, which can result in variability in the properties of the grout. This may require additional testing and monitoring to ensure that the desired properties are achieved.

Risk of damage to existing structures: Jet grouting can generate significant vibrations and ground movements, which can potentially damage nearby structures or utilities. Careful planning and monitoring are required to minimize these risks.

Environmental considerations: Jet grouting typically involves the use of cement-based grouts, which can have environmental impacts if not properly managed. The use of alternative grout materials or careful management of the grout can help to minimize these impacts.