Injection drilling methods

Injection drilling methods

If there is a construction project for which the foundation soil does not fulfill the geotechnical requirements, this soil must be stabilised.

This improvement of foundation soil can be accomplished through cement stabilisation. Different methods are used to inject the cement into the foundation soil to improve its geotechnical properties. One way to perform this cement stabilisation is to use what is known as ‘jet grouting’, or else high-pressure injection drilling.

This method involves sinking a borehole tailored to the conditions of the foundation soil in question. Once the intended depth is reached, the system switches to jet grouting. Suspension is discharged from the jet at high speed, cutting the existing soil. The drill pipes and jet are continuously retracted upward throughout the process. The suspension mixes with the loosened soil, creating a column.

In jet grouting, a basic distinction is made between single-phase, double-phase and triple-phase systems. A single-phase system works with a single medium, typically a cement-containing suspension. The jet cuts and grouts the soil simultaneously. The suspension is supplied at pressures of 200-600 bar. Double- and triple-phase systems inject air and air/water in addition to the cement-containing suspension. These additional media make deeper cuts in the soil to permit the cement-containing suspension to penetrate even deeper into the ground. This permits columns with greater diameters than those created with a single-phase system.

Another way to stabilise the soil through grouting is to apply mechanical-hydraulic mixing processes. These processes are mostly known under the term ‘deep soil mixing’ (DSM). This method can be used to stabilise large masses of soil. A rotating mixer in vertical motion is used to mix a suspension of bonding agent with the soil.