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Jet grouting



Jet grouting is a versatile and effective technique which can be used across a wide range of ground conditions.  It involves the insitu mixing of soils with cement grout to form  a predetermined strength / permeability matrix. 
The inclusions formed by this process may be  used for structural support, or for the control of  groundwater.


Cementation developed Jet Grouting in the 1960's for ground water control applications in the Middle East and Africa. The process involves the insertion of a special drilling tool to the required depth using a rotary drilling technique, followed by carefully controlled  grout injection whilst rotating and withdrawing.
The column is formed by the action of the high pressure grout eroding the in-situ ground perpendicular to the angle of insertion to a predetermined radius around the tool.
The eroded material is mixed with the grout to form a soil-grout matrix.
The strength and permeability of the columns can be controlled by the water / cement ratio and the addition of admixtures to the grout. The diameter of the columns is controlled by the rotation and lift speed of the drill tool.

Jet grouting systems are traditionally divided into three categories, depending on the number of injection nozzles and the medium used to erode the soil:

Single system - Grout is pumped down through the drilling rods and exits horizontal nozzles in the tool at high velocity. This causes erosion of the ground and the placement and mixing of grout in the soil. This method produces the most homogeneous soil-cement element with the highest strength and the least amount of grout-spoil return, but can cause heave problems in certain ground conditions.

Double system - A two-phase internal system is employed for the separate supply of grout and air down to different, concentric nozzles. Grout is used for eroding and mixing with the soil. The air shrouds the grout jet and increases erosion efficiency. The double system is more effective in cohesive soils than the single system. However, the presence of the air reduces the strength of the column as compared to the single system, and the 
air produces greater spoil returns.

Triple system - Grout, air and water are pumped through three different lines to the tool. High velocity coaxial air and water form the erosion medium. Grout emerges at a lower velocity from separate nozzles below the erosion jet. This somewhat separates the erosion process from the grouting process and yields a higher quality inclusion. The triple system is the most effective system for cohesive soils, and because the grout replaces a substantial portion of the eroded soil, it is less likely to cause heaving of the ground.




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