The three basic jet grouting systems are single-fluid (grout only) double-fluid (grout and air) and triple-fluid (grout, air and water): selection of the most appropriate system is dependent on the in situ soil characteristics and the application.  The single-fluid is typically used where a large column geometry is not required or where air may have an adverse effect on surrounding soils or structures. For large scale areal treatment such as groundwater cut-off or containment of contaminated waste, where a reduction in hydraulic conductivity is the primary objective, the double system may be most applicable. For soil stabilization and underpinning/excavation support, where a high strength product is the goal, the triple system may be the most appropriate.

Jet grouting can be performed above or below the water table and in soil conditions ranging from coarse sands and gravels to plastic clays.  Various geometries of soil-cement product can be created, and jetting can be performed at angles up to 30° from horizontal to facilitate access to target soils beneath underground or surface obstructions.

Installation

Jet grouting is accomplished using a purpose-built system  consisting of a drill rig, drill steel incorporating a jet grout monitor, high-volume mixing and batching equipment, high-performance pumps, large air compressors, and an automated jet grout control and data acquisition system.

A jet grout column is constructed by advancing a borehole to the bottom of the planned treatment zone using rotary or rotary percussive drilling methods. Grout injection then commenced as the tooling is extracted with controlled rotation and withdrawal speeds.  The process effectively erodes the soil and mixes it with the injected grout slurry.  Installation of individual columns is sequenced to allow sufficient curing time prior to installation of intermediate overlapping elements.  Jet grout panels are constructed in a similar manner except that the jetting rods are only rotated at limited angles during withdrawal.

Applications

  • Soil stabilization
  • Groundwater cut-off
  • Underpinning/excavation support
  • In situ soil solidification
  • Homogenization of a mixed face tunnel
  • Tunnel eye stabilization
  • Closure of conventional excavation support systems
  • Bottom seals
  • Contaminated waste containment

Advantages

  • Can be performed vertically or at an angle above or below the water table
  • Can be performed in most soils
  • Irregular geometries such as half columns or panels can be created
  • Can be targeted to a specific soil zone
  • Angled jet grouting can facilitate construction in limited headroom areas.

Limitations

  • Local obstructions such as cobbles or boulders can result in “shadowing” leading to incomplete soil-cement geometries.
  • Considerable volumes of spoil are generated that must be channeled to a holding pit and allowed to set up before disposal in accordance with the project specifications.

Project summaries for jet grouting applications include Harlem River Tunnel and White Plains MPG.