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Grouting includes a range of processes that involve the injection of wet or dry materials into the ground to provide improved engineering properties. Common aims are to increase strength or stiffness or to reduce permeability within the mass of ground treated. The simplest process in concept is the permeation of the pore spaces with a fluid grout which then sets, and provides the desired properties. Jet grouting employs erosion and mixing using high energy jets, to attack a wide-ranging set of soils and applications. This paper, mainly, addresses permeation grouting for the improvement of soils, in terms of strengthening or reduction of permeability, and compensation grouting for the displacement of structures during subsurface exploration. The historical evolution of these two grouting processes is described leading up to present-day practice. Reference is made to grouting materials, methods of injection, equipment, limitations and verification for each type of grouting. The grouts used to make permeation grouting are mainly suspensions and chemical solutions. The suspensions penetrate well into soils with granulometry up to coarse sand. On the contrary, the chemical solutions penetrate satisfactorily in finer formations up to fine sands or coarse sludges. Because some chemical solutions are toxic or generally harmful to the environment and humans, an effort has been made internationally in recent years to replace them with inorganic fine-grained suspensions.

Grouting includes a range of processes that involve the injection of wet or dry materials into the ground to provide improved engineering properties. Common aims are to increase strength or stiffness or to reduce permeability within the mass of ground treated. This paper, mainly, addresses permeation grouting for the improvement of soils, in terms of strengthening or reduction of permeability, and compensation grouting for the displacement of structures during subsurface exploration. The grouts used to make permeation grouting are suspensions and chemical solutions. The suspensions penetrate well into soils with granulometry up to coarse sand. On the contrary, the chemical solutions penetrate satisfactorily in finer formations up to fine sands or coarse sludges. Because some chemical solutions are toxic or generally harmful to the environment and humans, an effort has been made internationally in recent years to replace them with inorganic fine-grained suspensions.

Unconsolidated–undrained (single and multi-stage) triaxial compression tests were conducted to evaluate the shear strength of microfine cement grouted sands. Microfine cements of three different types were obtained by pulverising ordinary cements produced in Greece. Multi-stage triaxial compression tests can be used dependably for determination of the shear strength parameters of cement grouted sands. It has been observed that the Mohr–Coulomb failure criterion represents adequately the behaviour of the grouted sands. Grouting with microfine cement suspensions improves the strength of sands significantly, and the improvement is primarily controlled by the water-to-cement (W/C) ratio of the suspensions. The positive effect of microfine cement grouting on the shear strength of sands is mainly the addition of cohesion, which is substantial even at a distance of 1·2 m from the injection point. Grouting with suspension, using W/C = 1 provides the sand with cohesion of about 2·6 MPa. The shear strength parameters vary with axial strain, and cohesion attains a maximum value well before failure.