Ground improvement jet grouting

Jet grouting or high pressure grouting is an erosion-based grouting technique using a high-pressure jet of grout to break up the soil structure and simultaneously mix the loosened soil with a cement grout to form so-called ‘soilcrete’ (grouted soil - cement soil) column-shaped bodies, panels or half-columns. The distinct advantage of jet grouting is to significantly increase the strength of the soil treated and / or reduce its permeability. Construction sequence 1. & 2. Drilling phase: using a jet grouting drill string - at its bottom equipped with a special drill bit - a small hole is drilled to the design depth of the treatment through injection of water or cement grout. 3. Jetting phase: cement grout at very high pressure (400 bar) is pumped above the bottom of the drill tube where it emerges through very small diameter orifices or injection ‘nozzles’ (diameters from 1.5 to 4 mm) into the soil, converting the energy from high pressure to very high velocity and disintegrating the soil structure over / across a specific distance. The jet erodes the soil as the drilling rod and drill bit are kept rotating and slowly pulled up at a controlled rate. 4. In the soil, a cylindrical ‘soilcrete’ column is formed by a homogeneous mixture of injected cement grout and soil. Upon reaching the desired column height, jetting is stopped and the tube is withdrawn. 5 & 6. Formation of an injected ‘jet grout’ body/wall. A central reinforcement bar, a reinforcing cage of limited dimensions or a steel profile can be inserted into the freshly formed grout column.