Jet Grouting

Construction sequence:
A string of jet grouting rods is drilled into the ground to the required depth by a rotary drilling rig. The lower end of the drill string is fi tted with a nozzle holder and a laterally mounted jet grouting nozzle.

A jetting fluid (usually a cement grout, depending on the type of jet grouting system) is pumped through the jet grouting nozzle at high pressure (400 - 600 bar). This produces a high-energy „cutting jet“, which erodes the soil from its natural position and mixes it with the grout. The diameter of the column is determined by the density and type of soil, as well as the jet grouting parameters.

By rotating and simultaneously retracting the jet grouting drill string, the cutting jet describes a tightly spaced helix in the soil, resulting in a column-shaped space filled with grout and soil. The cement grout causes this mixture to set and solidify, as a result of which load-bearing jet grouting columns are formed.

Jet grouting systems and sequences
Depending on site-specific circumstances, and the prevailing soil conditions (granular and/or cohesive) the system and sequence must be determined for each individual project, to ensure the required quality.

Jet grouting systems:

Single system: Process in which the disaggregation of the soil and its cementation are achieved by a high-energy jet of a single fluid, usually a cement grout. An adequate column diameter is already achieved with this system in homogeneous soils.

Double (air) system: Process in which the disaggregation of the soil and its cementation are achieved by one high- energy fluid (usually a cement grout), assisted by an air jet shroud as a second fluid to maintain the energy of the fluid jet over a longer distance. Wherever air support is advisable, larger column diameters can be achieved compared to the single system.

Triple system: Process in which the disaggregation of the soil is achieved by a high-energy water jet, assisted by an air shroud, both aimed to achieve a larger column diameter. Its cementing is simultaneously obtained by a separate noncutting grout jet.

Sequence:

The execution of continuous jet elements can be achieved by single columns executed in the runner sequence, or by single columns executed in the pilgrim step mode. A fresh- in-fresh sequence aims to further integrate the individual columns of the longer planar elements.