What is high pressure injection or jet grouting? (Jet Grouting)
rose roofing: High-pressure injection or jet grouting is one of the relatively new methods of pit stabilization and soil improvement. In this method, by increasing the bearing capacity of the soil in situ, the characteristics of the soil are modified. High pressure injection method (jet grouting) was used for the first time in Japan. In the early 1970s, high pressure water jet cutting was investigated in American and British coal mines. The Japanese Yamakado brothers in 1965 used this method not only for cutting but also for cement injection.
In the high-pressure injection method (jet grouting):
After drilling the borehole to the depth desired by the designer
Cement slurry with compressed air under very high pressure of 250 to 700 bar
with a speed of over 100 meters per second
It comes out from the nozzle at the end of the drilling rod and at the same time as the drilling rod rotates, the soil around the place of exit of the compressed air mixture is destroyed and compressed and mixed with it. In this way, a cement column with high resistance is created.
Injection specifications in jet grouting method
Characteristics of injection in the jet grouting method – soil improvement
The steps of high pressure injection (jet grouting) – Istasazeh Engineering Company
The steps of high pressure injection (jet grouting)
High pressure injection (jet grouting) to stabilize the soil
High pressure injection (jet grouting) to stabilize the soil
High pressure injection (jet grouting) for sealing
High pressure injection (jet grouting) for sealing
High pressure injection is generally performed in 3 ways based on the number of fluids used:
Single fluid: in this method, at the end of the drilling operation, the discharge valves are closed and the injection mixture is injected into the soil with very high pressure (up to 600 bar) through the nozzles, and at the same time, the rod is rotating to moves up. In this way, the injected slurry mixes with the surrounding soil at high speed and energy.
Single fluid high pressure injection – Ista Sazeh Construction Company
Single fluid high pressure injection
Double fluid: The method of performing high-pressure injection cement column (jet grouting) in this method is the same as the single-fluid mode, with the difference that when performing the high-pressure injection operation (up to 600 bar), a sheath of compressed air under a pressure of 12 bar which is located in the environment of the slurry, it is injected into the soil at the same time as the slurry, which results in an increase in the energy of injection and an increase in the penetration radius of the mixture, and finally we will have a higher diameter obtained in different soils.
Double fluid high pressure injection
Double fluid high pressure injection
Triple fluid: In this method, water under high pressure (up to 600 bar) is injected into it in order to break the structure of the soil. Then the slurry is injected with a pressure of 40 to 70 bar from another nozzle in the desired area and mixed with the soil.
Triple fluid high pressure injection
Triple fluid high pressure injection
Choose one of the above 3 methods based on:
Soil type
Physical properties
Expected type of use of cement soil mass
will be done.
In addition, the type of connections (watersville, etc.) and nozzle (monitor) are different in the three mentioned methods.
3 conventional modes of high-pressure injection (jet grouting) – soil improvement – Ista Sazeh Engineering Company
3 conventional modes of high-pressure injection (jet grouting) – soil improvement
According to the amount of fluid used in the high-pressure injection method, the compressive strength of the cement column changes.
In the article (Kauschinger et al., 1989), the compressive strength of several samples of cement columns has been obtained:
The type of soil is single fluid, double fluid, three fluid
Sandy soils 10-30 7.5-15 10-20
Clay soils 1.5-10 1.5-5 1.5-7.5
Compressive strength of cement columns by jet grouting method in megapascals
Basics of high-pressure injection method design (jet grouting)
Like other vertical bearing members such as piles, the benefits of using the high pressure injection method are as follows:
Increasing the bearing capacity of soil in pressure and shear
Seat control
Dealing with liquefaction
Decreased permeability
In order to calculate the effect of high pressure injection on each of the above goals, as well as other vertical load bearing members, various relationships have been presented in geotechnical engineering. As an example, to calculate the allowable geotechnical bearing capacity of high-pressure injection columns, the frictional resistance and tips of these columns are used. The capacity of these columns is equal to at least two values:
Allowable geotechnical capacity
Allowable structural capacity
is. The permissible structural capacity of these columns can also be calculated based on one of the following two methods:
Uniaxial resistance of the cores obtained from the column
Large scale loading of columns
Therefore, one of the important parameters for the design of high-pressure injection columns is the unconfined compressive strength of the soil and cement mixture resulting from this method.
Capacity of high pressure injection columns
The capacity of high-pressure injection columns = their minimum allowed geotechnical and structural capacity
In order to verify the design, a high-pressure injection column can be implemented in the project and by sampling from different depths of this column, the 28-day strength of these samples can be obtained and the initial design modified. The compressive strength of cement soil is directly related to:
Soil type
The amount of cement used in the grout
has it.
Applications of high pressure injection method (jet grouting)
As shown in the figure below, the high-pressure injection method can be used in a wide range of soils to improve and stabilize the soil. The jet grouting method has various applications, some examples are mentioned:
Repair and reconstruction of foundations
Guard structure to stabilize pits
Sealing pits and structures below the groundwater level
Underpinning
Dam water wall and excavation
As a foundation for structures in loose soils
Improving and increasing the bearing capacity of structure foundations e
