The process of manufacturing cylindrical columns from a mixture of ground material and cement by drilling the ground with a drilling machine and mixing the high-pressure cement grout with the ground by spraying it is called the jet grout method .
The soil-cement mixture is a cementitious chemical mixture and it causes serious increases especially in the shear strength of the ground. In order to increase the effect of these mixtures created by high pressure injection, substances such as fly ash and sodium sulfate can be added to the mixture.
Walls and diaphragms can be built underground with the other jet grout columns applied next to the well without leaving any space in between, without setting the column we have created with the jet grout method, which is applied from the ground level of the well upwards .
The mechanical and geometric properties of the columns to be formed by the jet grouting method depend on the soil parameters to be applied, the method by which the application will be made, and also on the variable parameters and method properties in these methods.
Jet Grouting Advantages
Jet grout method can be used on almost any weak ground and sand, clay, gravel etc. It is a highly preferred ground improvement method with its applicability in ground structures formed by natural soils, as well as providing a more economical, permanent, fast and reliable solution compared to other improvement methods.
Jet grout method is a faster, reliable, permanent and economical solution alternative than other improvement methods in combinations of natural soil elements in almost all types of weak soil types.
Jet grouting method increases soil bearing capacity, reduces settlement, liquefaction risk and permeability. It is one of the most up-to-date ground improvement methods and it is economical, fast to be applied, versatile, etc. Due to the advantages of the Jet Grout Method, its use is becoming more and more widespread.
Jet grout method applicable to all floor materials (with some exceptions). It has light and small equipment. Thanks to its abrasive effects, it is more efficient than the classical injection method. It provides ease of working with small machines in the desired place. It does not make vibration, noise, does not harm the environment by not using chemicals and provides the opportunity to work near existing structures. It provides safety in high-risk construction sites. There is no deformation in the foundation reinforcements or it is within the tolerance values. It provides a lot of convenience in planning, the amount of material, time and cost can be predicted clearly. With a very small injection hole (≈10 cm), floors can be improved in large areas (1 – 8 m²). It can be started at the desired depth and completed at the desired depths. Preparation and supply of materials is very simple. Vertical columns can be made with the Jet Grout Method , as well as horizontal and inclined columns. Production times can be shortened between 30% and 60% according to the field conditions. It has been determined that the SPT values of the untreated soils around the columns have improved by around 20% – 25%.
If we want to list the Advantages of Jet Grout Method in items;
- It is faster and more economical than conventional injection methods.
- It can be applied to almost all types of floors.
- It does not have harmful side effects on existing structures, pressure spraying only affects its own radius and does not damage adjacent structures.
- Due to the flexibility of the machine, injections can be made in different geometries. It is suitable for horizontal inclination and vertical application.
- Since water/cement is used, it does not harm the environment like chemical injection.
- Thanks to its equipment dimensions, it can easily work in narrow and cramped environments.
- Injection can be started from the desired depth and finished at the desired depth.
- It is a vibration-free and noiseless method.
Jet Grouting Disadvantages
The diameters and strengths of the columns vary within themselves. Column diameters can vary from floor to floor. This change has to be taken into account in the calculations. In two and three fluid systems, maintenance and repair costs can increase as more complex parts are required. In addition, more than 10º-20º slope is not allowed in these systems. Since old experience and literature are used in design, instant interventions may be required in practice and situations that are not suitable for the design may arise. At very high pressures, it can cause cracking of soil materials and settlement in surrounding buildings. This leads to the need for frequent controls, the need for more experienced personnel, the need for frequent spray nozzle control, the need for controlled damping of high pressure, the need for frequent maintenance and cleaning.
Disadvantages of Jet Grout Method;
- The method is still under development. As the method is new, the rules to be used in the design have not been finalized yet. For this reason, it is a method based on experience and observation.
- It is difficult to determine the column that will form in the ground. Therefore, it needs to be done carefully and some control tests need to be done.
- Column diameters may be different depending on the soil type.
- In two-fluid and three-fluid systems, a maximum inclination of 10º-20º can be created. The reason for the formation of this limitation is to ensure that the disturbed material on the ground is taken out with the sprayed air.