Jet grouting

Jet-grouting injection involves rotating columns forming using a concentrated stream of cement slurry injection. This technology, thanks to the use of very high injection pressures (400-600 bar), produces a stream of very high energy, which leads to erosion, loosening and cementation of the soil at the assumed distance from the drilling axis. Depending on the ground conditions, the material resulting from mixing the grout with soil (the so-called cement-soil) can reach strength from 1 to 30 MPa. Thanks to the ongoing control of the pressing parameters, the contractor has continuous control over the diameter and strength of the formed columns.

Origin

In its original version, this technology was developed at the turn of the 1960s and 1970s in Japan as CCP (Chemical Churing Pile) piles. Due to the large possibilities and a wide range of applications, the technology quickly spread outside Japan in the countries of America and Europe. In the following years, the technology was repeatedly improved by successive contractors.

The first implementations with the use of high-pressure injection in Poland date back to the beginning of the 90s. Until then, the safety and reliability of properly made columns have been confirmed by countless implementations. The experience gained since then makes the contractor able to propose technologically and economically advantageous use of the Jet-Grouting technology as a replacement solution to other technologies of piling or securing the excavation.

How To Do

There are three steps to making a Jet Grouting column:

Drilling & nbsp; – In the case of the Jet Grouting method, it is performed using any type of drilling rig (from small-size or manual drilling rigs to piling rigs). It consists in hammering and rotary driving the drill rod into the ground. A drill bit with a diameter of 10 cm is selected according to the expected ground conditions and obstacles. It is possible to drill through any soil (including rock interfaces) or unreinforced foundations. Typically, drilling is done under cover of cement slurry or water.

Injection & nbsp; – After reaching the set depth, you go to the next stage. The injection is made from the base upwards. During the rotation of the rod, the grout injection and additional cutting media are fed under high pressure. The power of the stream is so great that the soil around the pole is thoroughly mixed to form a uniform column. During the pulling process, the excess material from drilling is brought to the surface in the form of a technological dump.

Reinforcement assembly & nbsp; – After the injection is finished, depending on the project requirements, it is possible to reinforce the column. The assembly is carried out by pressing the reinforcement with an excavator, or vibrating with a small vibro-hammer. The most commonly used are HEB, IPE or pipes.

Injection method

Jet-Grouting technology has been improved many times over the years. As of today, there are three basic varieties:

Single-wash system – only cement slurry is used to form the column. It works well in difficult access conditions, where drilling with small-size drilling rigs is required, or when the designed columns are to reach a diameter of up to 80 cm.

Two-fluid system – unlike the single-fluid system, the loosening and cementation processes are separate. This is achieved thanks to the use of an additional compressed air stream, which is ahead of the slurry stream, loosening the soil. The resulting columns can be characterized by lower cement consumption and larger diameters than when using a single system.

Triple system – it is based on the operation similar to the double system, with the exception of a loosening stream composed of high pressure air and water.

Advantages of the technology over alternative piling methods

Due to the possibility of drilling with small-size equipment, Jet-Grouting columns can be used in almost any space. Thanks to this, the columns can be built from the basements of existing buildings or narrow yards that would not fit the equipment for other piling technology.

Since drilling is done with conventional anchor rigs, there is almost no limit to the angle at which the columns are to be made. This is especially useful for foundations loaded with high horizontal forces. In extreme cases, you can even find horizontal columns in the roofs of tunnels.

Due to the thorough washing of obstacles in the ground with a stream, it is possible to create walls or cut-off plugs out of interlocking columns. It is often the only solution to stop the inflow of groundwater.

A positive side effect of high-pressure injection is the formation of a jagged mace that mobilizes much greater friction on the side surface than piles implemented in other technologies. As a result, the Jet-Grouting column with the same parameters will achieve greater load capacity than other piles, e.g. in drilled technologies.

Top Uses

Columns are most often used to support existing foundations. They are used when the building suffers damage as a result of subsidence or will be adjacent to a deep excavation.

The second most common application is in the sealing of deep excavation linings and flood protection dikes. Depending on the arrangement of permeable layers, vertical or horizontal screens are made to protect against the inflow of groundwater.

Jet-Grouting columns, due to their high load-bearing capacity obtained thanks to the jagged side surface, may be an attractive alternative to piles drilled with other technologies. Each time such a case requires a computational analysis.

The above-mentioned examples of use show only the most common implementations made with the use of Jet-Grouting columns. Drilling possibilities allow for much wider applications, e.g. securing the ceilings of tunnels, stabilizing landslides or securing excavations.

In order to learn more about the possibilities of technology, please contact us.

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