Grouting is the process of injecting grout material into interconnected pores or void space. Which occurred during the blasting of the face of the tunnel, the grout material may be a cementitious, resinous, or solution of a chemical mixture. In any section of the underground structure, the concrete lining within 100m of the section shall have been in place for at least 21 days before grouting commences.
Types of grouting
- 1) Contact grouting
- Low-pressure contact grouting carried out between concrete and rock over the entire length of the tunnel to fill voids between the rock surface and concrete lining.
- Contact grouting is done at low pressure (up to 5 bar) using cementsand grouting.
- Water pressure testing is not required for contact grouting.
- Contact grouting is normally done from holes drilled in the crown of the tunnel, shaft, and cavern.
- After the grouting of any hole is completed, the pressure should be maintained, by means of a stopcock or other suitable devices, until the grout has set.
- Consolidation grouting
- Consolidation grouting of the rock surrounding the excavated hollow space, which is done after the concrete lining of tunnel and completion of contact grouting.
- Consolidation grouting is done at pressure up to 30 bar.
- Length of drill hole should be of 4m to 5m.
- Grout shall normally consist of a water- cement slurry (w/c=.5 to 1) with admixtures and possibly with bentonite.
- Cement-sand grout, possibly with admixture
- Chemical grout such as Polyurethanes
- Cement-bentonite grout with or without sand
- The quantity of sand, bentonite and admixture are depending on the permeability of rock and the size of voids tube grouted.
- Admixture shall be added to grout mixes to optimize the strength, viscosity, density, setting time and shrinkage.
- Polyurethanes shall be used for consolidation of the disturb rock, loose material, and for impermeability against water inflow even under high pressure.
- All holes for consolidation and contact grouting shall be 38 to 40mm minimum in diameter, where for curtain grouting shall be minimum 45mm.
- Entire temporary drainage system shall be filled with grout.