In the recent years the shield method has been greatly improved and thus reliable back-filling become a very important problem for successful construction. The back-filling metarials currently used, however, have such undesirable tendencies as run-off into natural ground, flow-out to the face, dilution by water, etc..
In order to overcome these weaknesses, a new grouting material and a new injecting system with it have been developed.
The main component of new grouting material is one type of silica-gel which is formed mixing silica-sol, particular cement and aggregates. In the new grouting method, a small amount of new grouting material is added to the back-filling slurry during its transmission by adopting a new mixing system, 1.5 shot of proportion type. Through this mixing process, the liquid material becomes a solid state of thixotropical-gel; in the state the material does not flow by its own-weight but easily flow by the action of pumping pressure.
In order to compare effectiveness of the new grout and grouting system with that of the grouts and systems currently used, outdoor grouting tests were carried out use of a large-scale model mold. The results showed its great resistances against dilution by water, bleeding, segregation, flow-out and run-off.