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Rock grouting

 

Rock grouting tends to be used to fill fissures in the rock, reducing the amount of water that filters through the rock mass. It is usually carried out with a single packer that is inserted into the previously drilled bore to the pre-established level; grouting is carried out and then the packer is raised by stages, normally every 5m, until grouting of the bore is complete. Grouting has traditionally been carried out with cement-bentonite mixes, and occasionally microcement is used.

GEOCISA has extensive experience in grouting of this type, having carried out a large amount of grouting in dam foundations.

This type of grouting with cement-bentonite mixes in dam foundations is currently being replaced by a new system, the ground intensity number (GIN) method, designed by G. Lombardi, which has been pioneered in Spain by GEOCISA, following the creator’s directives. GEOCISA has developed instrumentation and software to control the GIN grouting process.

The two basic characteristics of the GIN method are as follows:

  • The grouting mix must not contain bentonite; instead a stable cement grout mix should be used with a super plastifier to lower the viscosity of the mix, reduce the “cohesion” value and turn the grout mix into a Bingham fluid.
  • To minimise the risk of hydraulic fracturing of the rock mass, as well as limiting the grouting pressures and volumes, the injection interval is limited by the hyperbole P•V=constant