Injection technique is used in civil engineering to improve the mechanical and permeability properties of soil, rocks and brick or concrete work.
From a functional point of view, two types of interventions can be identified:
• temporary intervention, to make excavation possible in unstable soil or under water table;
• permanent intervention for the consolidation of foundation soils, the creation of watertight structures, or the structural restoration of brick or concrete works.
From an operating point of view, grouting is divided into loose soil grouting and in rock grouting.
Rock fissure grouting is performed directly into the open borehole. In this case, downstage or upstage methods can be used. In both cases, borehole inclination must be defined depending on the position of soil layers and the direction of discontinuities, so as to affect the highest number of joints or fissures.
Grouting in weathered rocks or loose soil can be performed by using tubes fitted with check valves, which are driven into the ground after drilling. The valves are usually rubber sleeves that cover lengths of the tube featuring holes: they inflate under pressure and force the grout through the holes preventing it from flowing back.
Cement-based grouts are usually the choice for rock formations or loose coarse-grained soils. Cement grouts can be stabilized by means of prehydrated bentonite, whereas they are made less cohesive and more fluid by adding special formulations and deflocculating-fluidifying additives (MISTRA grouts). There is evidence in literature that successful grouting depends in the first place on the size of the solid particles of the injected grout compared to the dimensions of the gaps or rock fissures to be injected.