JET GROUTING

JET GROUTING is a soil improvement technique has been used since the early 1970s in many countries of the world. This technique consists of the formation of grout piles and walls. It may be applied to all types of soils including low permeable fine-grained cohesive soils or weathered and soft rocks. The technology is used for the construction of overpasses and bridges, harbour engineering, strengthening of building foundations, embankments and slope stabilization.

It can be performed in many ways. One procedure consists in using a special drill bit with vertical and horizontal high-pressure water jets to excavate through the soil. Cement based grout is then forced through the lateral jets to mix with the small remaining amount of foundation material loosened during excavation. When the grout sets the end result is a fairly hard, impervious column. This procedure is somewhat similar to the soil-cement columns.

There are at least four procedures for producing jet-grouted columns, but the two principal methods are 1. Breaking up the soil and mixing it in situ with the grout. A borehole of about the same diameter as the grout rods is used and grout columns up to about 1 m in diameter can be produced.

Jet Grouting Nozzles

2. Breaking up and partially removing the in situ material—usually using boreholes much larger than the grout rods—so that the resulting column is mostly grout. Grout columns up to about 3 m in diameter can be produced by this method.

The grout columns (also called grout piles) have been used considerably in underpinning structures to provide additional foundation support. The method is also used for general foundation improvement, and very small diameter shafts are sometimes called root piles. Closely spaced columns are sometimes used for excavation support (but would require the insertion of reinforcing rods in the wet grout for bending resistance) and for groundwater control; however, the soil-cement columns previously described are probably better suited in most cases. A more comprehensive description of this method is given in ASCE SP 12.