Among other technique of stabilization techniques, the grouting is one of the most expensive methods where some kind of stabilizing agent inserted into the soil mass under pressure. The pressure forces the agent into the soil voids in a limited space around the injection tube. The agent reacts with the soil and /or itself to form a stable mass. The most common grout is an admixture of cement and water, with or without sand. It has a large number of applications such as:
1. Control of water problems by filling cracks and pores.
2. Prevention of sand densification beneath adjacent structures due to pile driving.
3. Underpinning using compaction (displacement) grouting.
4. Reducing vibrations by stiffening the soil.
5. Reducing settlements by filling voids and cementing the soil structure more firmly.
Generally grout can be used if the permeability of the deposit is greater than 10 -5 m/s. one of the principal precautions with grouting is that the injection pressure should not be sufficient to lift the ground surface. In using compaction grouting where a very stiff displacement volume is injected into the ground under high pressure, however, lifting of the ground surface as a grout lens forms is of minor consequence.
Various chemicals can be used as grouting agents. Chemical agents are the most expensive foundation treatment of all. They do have advantages in that they have low viscosity and absence of particulate material, and the setting time can often be controlled.
Chemical stabilization in the form of lime, cement, fly ash or combination of the above is widely used in soil stabilization for road and street work. It can also be used for building construction to improve the soil. Lime, foe example, will reduce the plasticity of most days, which in return reduces volume-change potential. Mixtures of cement, cement and fly ash, or lime, cement and fly ash can improve the bearing capacity of the soil considerably. The optimum benefit of using these agents in stabilization must be determined by laboratory testing. Beyond a certain optimum percent of stabilizing material the effect may be detrimental.