High-pressure grouting injection or jet grouting is one of the relatively new methods of excavation stabilization or earth retention as well as ground improvement. In The jet grouting method, by increasing the bearing capacity of the soil in situ, they modify the soil characteristics. The jet grouting method was used for the first time in Japan. In American and British coal mines in the early 1970s, cutting was investigated by jets with high-pressure water. In 1965, the Japanese Yamakado brothers used this method not only for cutting but also for injecting cement.
In jet grouting method:
- After drilling the borehole to the desired depth of the designer
- Cement slurry with compressed weather under very high pressure 250 to 700 bar
- At a speed of up to 100 m/s
comes out of the nozzle at the end of the drill rod and at the same time as the drill rod rotates, the soil around the exit point of the compressed climate mixture is destroyed and compacted, and mixed with it. This creates a high-strength cement column.
Jet grouting technique 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 drain valves are closed and the injection mixture is injected into the soil with nozzles at very high pressure (up to 600 bar) and at the same time, the rotating rod moves up. In this way, the injected slurry is mixed with the surrounding soil with high speed and energy.
- Double fluid: The method of execution of jet grouting cement column in this method is the same as the single fluid mode, with the difference that when performing high-pressure grouting operations (up to 600 bar) a casing of compressed air under pressure 12 bar in the slurry environment, simultaneously with the slurry, it is injected into the soil, which in turn increases the injection energy and increases the penetration radius of the mixture, and finally we will have a higher diameter in different soils.
- Triple fluid: In this method, water under high pressure (up to 600 bar) is first injected into it when the compressed air casing is under pressure around 8 to 12 bar to break the soil structure. The slurry is then injected at a pressure of 40 to 70 bars from another nozzle in the desired range and mixed with the soil.
Selecting one of the 3 methods above will be done based on:
- Soil type
- Physical properties
- Expected type of application of cement soil mass
Also, the type of connections (water-soil, etc.) and nozzles (monitors) are different in the three mentioned methods.
Depending on the number of fluids used in the jet grouting method, the compressive strength of the cement column changes
In the paper (Kauschinger et al., 1989), the compressive strength of several specimens of cement columns is obtained:
jet grouting Design
Like other vertical bearing members such as pile, the benefits of using the jet grouting method are as follows:
- Increasing soil bearing capacity in pressure and cutting
- Settlement control
- Dealing with liquefaction
- Decreasing permeability
To calculate the effect of jet grouting on each of the above objectives, like other vertical bearing members, various relations have been presented in geotechnical engineering. For example, to calculate the allowable geotechnical bearing capacity of high-pressure grouting columns, the frictional resistance and the tip of these columns are used.
The capacity of these columns is equal to at least two values:
- Allowable geotechnical capacity
- Allowable structural capacity
The allowable structural capacity of these columns can be calculated based on one of the following two methods:
- Uniaxial resistance of cores obtained from the column
- Large-scale loading of columns
Therefore, one of the important design parameters of jet grouting columns is the unconfined compressive strength of the soil-cement mixture obtained from this method.
To refine the design, a high-pressure injection column can be executed in the project, and by sampling from different depths of this column, the 28-day resistance of these samples can be obtained and the initial design can be modified. The compressive strength of cement soil is directly related to:
- Soil type
- The amount of cement used in the slurry
Applications of jet grouting method
As shown in the figure below, the high-pressure grouting method can be used in a wide range of soils to improve and stabilize the soil. The jet grouting method has several applications, some of which are mentioned:
- Repair and reconstruction of foundations
- Retaining structure to stabilize the excavations
- Dewatering of excavations and structures below groundwater level
- Underpinning
- Dam dewatering wall and excavation
- As a foundation in loose soils
- Improving and increasing the bearing capacity of the foundations of existing structures
- Use instead of pile
- Controlling and reducing the risk of liquefaction in loose and saturated soils
- Stabilization of gables
- Stabilization of soil and rocks around the tunnel
Quality control of jet grouting method
One of the important points in ground stabilization and improvement methods is to study the final conditions of execution, which is called quality control. Quality control tests the execution of the designer’s assumptions at the project site. Quality control can be performed on both the original and test members.
According to international standards (ASCE, EN) quality control in the jet grouting method can be done on the original and test columns. For this purpose, test columns are executed with different values:
- Injection pressure
- Injection steps
- Different mixing plans and so on
And the injection information is accurately recorded.
After determining the diameter and strength of the test columns, select the values of the column parameters whose diameter and strength are equal to the design assumptions, and the project jet grouting columns are executed with those parameters.
The necessary tests and controls during the construction of the final columns are:
- Material control tests before trapping
- Control tests after trapping
- Large-scale tests
Method of jet grouting execution
The first stage of jet grouting method is drilling a borehole and injecting cement slurry, which has the following characteristics:
- Rotational drilling with the diameter about 76 to 110 mm
- Water pressure: 20 bar
- Depth: up to the depth specified in the executive plans
The slurry is prepared in primary and secondary mixers and is ready for injection. Injection will be done in a rotational mode and in following stages:
- Stop
- Rotational jet grouting
- Pull out
For example, inject 8 rounds in 4 seconds with a pressure of 350 to 700 bar and then pull out 4 cm and repeat these steps. These numbers are designed depending on the desired geotechnical conditions and diameters. With these numbers, jet grouting columns are executed experimentally and then the diameter of the columns is measured to estimate the technical specifications of the project.
High injection pressure in jet grouting method, changes the soil structure and creates a strong soil-cement column. The radius of impact of the jet grouting, which sometimes reaches 3.5 m, depends on the following factors:
- Injection pressure
- Injection time
- Shear strength of soil in situ
- Nozzle size
- Specific gravity of injection slurry
- Soil type
- Rotational speed
- Upward movement speed of drilling rod
If, in addition to improving the soil, dewatering it is also desired, some bentonite can be added to the injection mixture.
Equipment required for jet grouting
The main equipments for executing this method are:
- Silo
- Mixing equipment
- High pressure pump
- Injection mixture pump (single fluid and double fluid method)
- Compressor (double and triple method)
- Drilling equipment
Advantages of jet grouting
high-pressure method is sometimes a good alternative to improvement methods such as preloading, pile execution and dynamic methods. Due to the existence of loose and settable coastal lands in Iran that are prone to liquefaction and subsidence phenomena, the need to improve the bed is quite obvious.
Jet grouting method, which can be used in a wide range of soils, is a good option for improving such soils.
Among the advantages of jet grouting method are the following:
- Converting ground into part of the soil-structure system
- Ability to control and confirm the quality of work
- Lower cost of equipping the workshop than similar cases such as pile execution
- Very high execution speed
- Lower execution costs than similar cases
- Generating less noise and vibration in the urban environment than similar methods
- Reducing soil permeability
- Increasing soil resistance
- Reducing soil subsidence due to overhead
- Preventing liquefaction
- Ground improvement in situ
Animation of jet grouting method in soil improvement
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Federal Highway Administration (FHWA)
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