Barton et al (2003) demonstrates that injection pressures measured at the injection lance (the collar of the drillhole) in most cases do not correspond to the pressure of the grout in the actual ground. As long as there is a flow of grout, there is a significant drop of pressure in the immediate vicinity of the drillhole into the ground. Another important issue is to always have in mind that an injection operation is a cycle in which decisions are made with regards to specific criteria. These decisions are made at each step of the injection cycle. Therefore pre-injection is a type of work that requires continuous and experienced hands-on management during the works. The process of bleeding, in which the cement grains separate from the grout mix and clog the entrances to the fine joints, does not occur with a stable grout mix. For soil injection purposes one must consider closely which intended improvement effect and penetration mechanism that is planned when designing the grout mixes and the method. Four examples of soil improvement mechanisms are shown in figure 4. Liquid colloidal silica grout type consists of silica grains (SÌ02) in the nanometric scale in a colloidal solution in water. The typical grain size is 0.016 pm. Its viscosity is 5-6 m-Pa-s, which is slightly higher than water. These technical properties offer a unique technical performance in a number of injection situations. Colloidal silica, contrary to silicates and acrylates, is a completely non-toxic product, which makes it unique in terms of environmental friendliness and health and safety. Colloidal silica is a mineral grout designed for permanent longterm purposes, whereas silicates only can have a temporary function. The second injection stage with the low viscosity grout could therefore be targeted for the finer joints and the joints which were partially filled with clay and silt. The secondary fan was injected with a termination pressure of 25 bars, or approximately 100kg grout per m drillhole. Injection beyond a pressure of 25 bars with liquid colloidal silica usually showed signs of hydrofracturing.