- Areas of Expertise
- Construction Methods
- Machinery & Equipment
JET - GROUTING APPLICATION
Jet - grout is a consolidation technique which is done through creation of injection of a cement water mixture to the ground under high pressure. Sandy or cohesive soils are mixed directly with the injected cement grout on site, ensuring a homogeneous and continuous consolidation.
2.0-) MACHINERY AND EQUIPMENT
- Jet - grout compatible drilling machine
- High Pressure jet - grout pump
- Automatic jet - grout mixer
- Cement silo
- Water tank
3.0-) CONSTRUCTION PROCEDURE
In drilling of jet - grout holes; hammer drilling, rotary drilling or a combination of the two methods are used. Additionally, pre-drilling is made by water jet and reverse circulation methods via forming larger diameter holes. The pressure and rotation force provided by the machine is then transferred to the drill bits at the tip of the drilling pipe. Clay and tricon tips are used in the drilling of plastic layers composed of smooth clay. During drilling - when necessary - the tip of the drill bits are closed, nozzles are assembled to the tip and pre-drilling is achieved.
Upon reaching the required depth, the tip of the drill bits are closed and a mixture of 1/1 cement water mixture is rapidly "jetted" into the ground through the appropriate diameter and number of nozzles. The applied pressure is around 300 to 600 bar, while the resulting high energy breaks up the surrounding soil forming the column together with the grout. The soil is hence consolidated and the mechanical properties are adjusted. Thanks to the pivoting movement of the drilling tool, the mixture forms a circular column. When this rotational motion is combined with the predetermined constant speed lifting motion, jet - grout columns are formed.
Jet - grout column form and sections depend on the following factors, in addition to the soil properties, listed below:
- Rotation speed,
- Lifting speed,
- Grout pressure,
- Nozzle number and diameter
- Grout flow rate
In order to be able to decide on these parameters, experiment columns are formed at the beginning of each job site.
3.2.1-) Jet 1 System
It is the most common and widely used method with injection pressure 300-600 bar. The resulting column diameters are approximately 600-800mm for clayed soils and 1000mm for sandy soils.
3.2.2-) Jet 2 System
This method is composed of two pipes inside one another. Water-cement mixture is supplied from the internal pipe, whereas compressed air is supplied from the external pipe. In this method, there exists less energy loss due to the compressed air and the column diameters are 60% larger than the Jet 1 system.
3.3-) Quality control
Load testing will be done if required.
The PIT (integrity) test will be performed if required.
A record card is prepared for each column. In these cards:
- Jet grout column number, location and date,
- Top and bottom of the column,
- Column diameter, drilling depth and jet-grout depth,
- Drilled soil profile and spoil amount are provided.
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