The technology „Jet grouting” is injection under high pressure of various chemical reagents – binders (strengtheners) which serve to improve the properties of the soil. The strengthener loosens the soil structure and mixes with it until it is a homogeneous mixture to form a stone-mass. This method is applicable to all types of soil, from clay to coarse gravel.
„Jet grouting” finds application in:
- strengthening the foundation of existing buildings;
- treatment the foundation of buildings near excavations;
- improving the ground foundation under increased loads or impermissible settlement;
- construction of vertical impervious walls;
- strengthening and consolidation the bottom of excavations;
- consolidation of the bottom under pipe channels;
- construction of horizontal columns - “umbrella” in tunnel construction;
- tunnel protection – creating a protective shell when passing through loose (and saturated) soils and near buildings;
- creating walls of round or polygonal shafts;
- joint sealing;
- strengthening of the soil in conducting parallel adjacent special geotechnical measures.
In the following figure are shown the stages of the jet grouting.
1 - Drilling a borehole; 2 - Reaching the required depth; 3 - Inserting and positioning of the discharge nozzle; 4 - Injection cement grout; 5 - Pulling the drill rod with rotating movements while continuing with the injection; 6 - completed grouted soil column.
There are three basic jet grouting systems:
- Single Fluid Jet Grouting (A) – the loosens of the soil is done only by the binder. The advantage of this system is the application in different work angles and protection of buildings and tunnels where the working space is limited. The process is used for small to medium sized jet grout columns in smaller depths. The single fluid jet grouting features a short preparation time and relatively low cost.
- Double Fluid Jet Grouting (B) – is mainly based on the single fluid jet grouting, but because of the increase of the injection radius is applied compressed air, which serves as a coating and is injected simultaneously with the strengthener. This system is applicable in greater depths.
- Triple Fluid Jet Grouting (C) – the soil loosening is done by a mixture of water and air under high pressure supplied through a special nozzle. The grout is injected simultaneously through an additional nozzle located below the water jet nozzle. The system is cost-effective in places with soil that is difficult to drill due to the fact that to achieve the same diameter and volume of the column with a single fluid jet grouting is necessary to implement several boreholes. The advantage of this method is that it is suitable for treatment of cohesive soils.
The geometrical form of the elements is determined by the movement of the drilling rod:
- pulling of the drill rods without rotation resulting in panels (lamella);
- partial rotating to form a segment - partial column;
- pulling and full rotating to create a cylindrical body – a complete column.
The mobility and the ability of implementation under all field conditions, the standardization of procedures and quality control at runtime are making the technology innovative and interesting measure for special geotechnical works.