Jet Grouting

1. & 2. Drilling phase: using a jet grouting drill string - at its bottom equipped with a special drill bit - a small hole is drilled to the design depth of the treatment through injection of water or cement grout.

3. Jetting phase: cement grout at very high pressure (400 bar) is pumped above the bottom of the drill tube where it emerges through very small diameter orifices or injection ‘nozzles’ (diameters from 1.5 to 4 mm) into the soil, converting the energy from high pressure to very high velocity and disintegrating the soil structure over / across a specific distance.

The jet erodes the soil as the drilling rod and drill bit are kept rotating and slowly pulled up at a controlled rate.

4. In the soil, a cylindrical ‘soilcrete’ column is formed by a homogeneous mixture of injected cement grout and soil.

Upon reaching the desired column height, jetting is stopped and the tube is withdrawn.

5 & 6. Formation of an injected ‘jet grout’ body/wall.

A central reinforcement bar, a reinforcing cage of limited dimensions or a steel profile can be inserted into the freshly formed grout column.

Real-time monitoring of the jet grouting operating parameters (height of the column, jet pressure, jet grout volume, rotation speed of the jet string, rate of withdrawal of the jet string)

• During jetting, a water-cement mixture injected under high pressure emerges through very small diameter nozzles, converting the energy from high pressure to very high velocity (kinetic energy). The controlled injection of grout at the bottom of the borehole tube causes:

• erosion and complete destruction of the granulometric structure of the soil which is cut, destroyed, disaggregated and loosened under the action of the jet grout

• washing of some excess soil to the surface under the action of the jetting fluid

• the addition of a binding agent to the soil mix

• By the hardening of the soil-cement mixture grout, columns with a substantial degree of compressive strength are formed and may therefore be used in structural walls and to form retaining and / or cut-off walls (earth and water retaining systems).

• The diameter of the formed grout columns depends on the nature of the soil and is determined by the diameter of the nozzles and the drilling parameters.

• Standard grout column diameters: from 300 up to > 1.000 mm

• By arranging the grout columns, either a secant grout column wall or an impervious jet grout bottom slab or plug is realized