The power delivered by the jet breaks up the native soil by erosion along a given radius depending on the type of soil and its compactness. Part of this soil is replaced by the cement grout brought by the jet. This replacement of a certain amount of native soil depends on the technique used and the final objective. The excess volume of mixture exits freely towards the surface during the process.
In the vast majority of applications, the equipment is rotated and raised so that the soil-cement component formed in situ is roughly cylindrical (a column).
The jet grouting process can be broken down into three different methods:
Depending on the jet’s parameters (flow, pressure and method used), the type of soil and the equipment used, the average diameter of the columns may vary between 60cm and several metres. Depths of up to 100m can be reached. The columns can be vertical, angled or even sub-horizontal.
A solution that adapts to all types of soil
A process that requires little space (small footprint and limited height)
Columns that can be constructed in contact with concrete or masonry structures
The ability to construct column sections by moving the jet to a specific angle without completely rotating it
The possibility of modifying the diameter of the column by modifying the parameters of the jet
The possibility of constructing large columns from small boreholes
Jet grouting is carried out using a drilling rig which injects a grout jet into the desired soil depth, in order to erode the soil around the rods and mix it with the grout up to a certain distance.
“Very high-pressure” equipment is used to pump the grout through one or more small-diameter nozzles placed at the end of the drill rods. A sudden reduction in diameter between the rods and the nozzle considerably accelerates the speed of the fluid to form a liquid jet.
A column is formed by rotating the rods and gradually raising them. This makes it possible to gradually create structures formed of several intersecting columns.
During the construction of a jet grouting column, the surplus materials (a mixture of soil, water and cement) are recovered on the surface for disposal in landfill.
In 2013, Soletanche Bachy constructed jet grouting columns on the edge of the crater of an ancient volcano in Lake Nyos, Cameroon