The high-pressure injection through nozzles (HDI) according to RODINJET patented system, opposed to the injection of pore filling at low pressure, causes a mechanical rupture and a remix of the soil structure in place.
The high pressure jet can create in the ground cylindrical (columns) or lamellar (in the absence of rotation of the rods) structures.
The jet grouting process begins with a small diameter drilling.
After reaching the planned depth, the drill pipe is rotated slowly, the injection pressure increases to 400-500 bar, creating an high speed fluid jet coming out from from a small nozzle placed on one side on the rods.
The soil is partially cut and remixed from the jet.
By extracting the drill rods at a controlled rate a cylindrical structure of cemented soil is obtained. The range action of of the jet depends on withdrawal speed of the rods, the eventual use of high pressure water jet (pre-cutting) or compressed air and on the shear strength (resistance) of the soil.
There are several jet grouting system and combinations, the three basic ones are:
• Rodinjet 1 system: high pressure cement grout jet
• Rodinjet 2 system: high pressure cement grout jet surrounded by a crown of compressed air
• Rodinjet 3 system: high pressure water jet surrounded by a crown of compressed air, cementation with cement grout occurs at lower pressure through a separated nozzle.
Generally speaking jet grouting columns can be tangent, overlapping or isolated.
Vertical, inclinated or horizontal jet grouting columns can be created. In the first and second case walls, slabs, blocks can be created.
Conical arches of overlapping jet grouting columns can be created to sustain the ground ahead of tunnel’s face.
Execution phases for one column:
1. Start of drilling;
2. End of drilling;
3. Start of jetting;
4. Low rotation and extraction of drill rods;
5. Completion of the column.
Horizontal jet grouting for the sustainment of excavation’s front:
If the stability of the cavity is not sufficient, support structures in ahead of tunnel’s face can be created by means of sub horizontal, jet grouting columns, in order to allow safe excavation.
(a) Single overlapping sub horizontal jet grouting columns create a sustaining arch
(b) Jet grouting columns sustaining the foundation of the upper arch